2024-03-29T05:01:45Z
http://digitalcommons.unl.edu/do/oai/
oai:digitalcommons.unl.edu:agronhortdiss-1000
2006-08-14T17:23:09Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
ASYMBIOTIC <i>in vitro</i> SEED GERMINATION, MICROPROPAGATION AND SCANNING ELECTRON MICROSCOPY OF SEVERAL TEMPERATE TERRESTRIAL ORCHIDS (ORCHIDACEAE)
Szendrák, Erika
Twenty-five different orchid species were successfully asymbiotically germinated and raised on a modified FAST medium (Fast 1976; Szendrák and R Eszéki, 1993). The development of geminating protocorms and young plantlets were recorded and compared among species. Spontaneous vegetative proliferation was also observed. Natural dispersed daylight and prevailing day-length were more favorable than l6-hour cool white fluorescent light for plantlet development. After two to three years of culture, the young plants were suitable for transfer ex vitro. The effects of organic compounds most commonly used for orchid micropropagation (peptone, coconut water, casein+lactalbumin and glucose) and medium consistencies were investigated for the development of temperate orchid protocorms from five species. Medium consistency had an important role in protocorm proliferation and development. In most cases, the liquid medium increased proliferation and the size of the protocorms. The media supplemented with the undefined organic compounds led to a greater proliferation rate and larger protocorms than the medium supplemented with glucose. In general, peptone and coconut water resulted in best development and proliferation of protocorms, but this varied with species. Anatomical structures and developmental patterns of seventeen temperate orchid species were observed by scanning electron microscopy (SEM). New information was recorded about the early stages of seed germination and protocorm development, the structural details of roots with mycorrhiza, stored materials (calcium oxalate crystals and starch), leaf/stem stomatal structure and anatomical details of the generative organs and ovule/seed development. Extensive SEM observations were also conducted on the seeds of more than 120 temperate orchid species. The length of the smallest seeds was ~200 mm (Spiranthes spp.) and the largest ones reached ~1700 mm (Cypripedium, Epipactis spp.) in length. Both quantitative and qualitative data were collected and detailed descriptions of the seeds of the different orchids were prepared. Several fascinating surface patterns and shapes were found, which were specific not only on the level of higher taxonomic units, but sometimes were distinctive even for the species or subspecies. Advisor: Paul E. Read
1997-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/1
https://digitalcommons.unl.edu/context/agronhortdiss/article/1000/viewcontent/Diss_1997_texted.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1001
2008-12-17T19:00:41Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Efficient Utilization of Water and Nitrogen Resources for Grain Sorghum under Rainfed Conditions
Abunyewa, Akwasi A.
Grain sorghum (Sorghum bicolor L. Moench) is the fifth world leading cereal after maize, wheat, rice and barley. The crop can yield reasonably well under adverse conditions of low soil water and high temperature. A three year field study was conducted in a transect across Nebraska where annual mean precipitation ranges from 300 to 900 mm yr-1 to evaluate management practices to optimize yield potential under water limiting conditions. Loss in grain yield due to planting configurations ranged from 20 to 30% with skip-row configurations compared to conventional planting configuration (s0) at the site with greatest precipitation. At a site with moderate precipitation, grain yield was reduced by 18% with plant two skip two configurations (s2) and was not significantly affected with plant one skip one configuration (s1). At sites with the lowest precipitation and significant soil water deficits, grain yield increased with s1 and s2 ranging between 5 and 123% over s0. Considering yield across all sites, s0 yield was greater than skip-row configurations when average yield was above 4.5 Mg ha-1. Water use efficiency was highest with skip-row configuration at low to medium in-season precipitation sites but lower at sites where the mean in-season daily precipitation was greater than 2.5 mm. Increased N rate resulted in increased grain yield with s0 but there were no significant response to N application after 100 kg N ha-1. With skip-row planting, raising N rate above 50 kg N ha-1 did not significantly increase grain yield. Conventional planting (s0) had significantly higher agronomic N use efficiency (AEN) and partial factor productivity of N applied (PFPN) than skip-row configurations. Water and nitrogen stress both resulted in significant increase of leaf and canopy reflectance. A model calibrated in a greenhouse study using a reciprocal index in the green and red edge and in the NIR ranges predicted chlorophyll content with RMSE ranging between 52 and 56 mg m-2.
2008-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/2
https://digitalcommons.unl.edu/context/agronhortdiss/article/1001/viewcontent/Abunyewa_Diss_OPTIMIZED.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1002
2009-07-22T22:00:29Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
An Integrated Crop- and Soil-Based Strategy for Variable-Rate Nitrogen Management in Corn
Roberts, Darrin F
Nitrogen (N) management in cereal crops has been the subject of considerable research and debate for several decades. Historic N management practices have contributed to low nitrogen use efficiency (NUE). Low NUE can be caused by such things as poor synchronization between soil N supply and crop demand, uniform application rates of fertilizer N to spatially variable landscapes, and failure to account for temporally variable influences on soil N supply and crop N need. Active canopy reflectance sensors and management zones (MZ) have been studied separately as possible plant- and soil-based N management tools to increase NUE. Recently, some have suggested that the integration of these two approaches would provide a more robust N management strategy that could more effectively account for soil and plant effects on crop N need. For this reason, the goal of this research was to develop an N application strategy that would account for spatial variability in soil properties and use active canopy reflectance sensors to determine in-season, on-the-go N fertilizer rates, thereby increasing NUE and economic return for producers over current N management practices. To address this overall goal, a series of studies were conducted to better understand active canopy sensor use and explore the possibility of integrating spatial soil data with active canopy sensors. Sensor placement to assess crop N status was first examined. It was found that the greatest reduction in error over sensing each individual row for a hypothetical 24-row applicator was obtained with 2-3 sensors estimating an average chlorophyll index for the entire boom width. Next, use of active sensor-based soil organic matter (OM) estimation was compared to more conventional aerial image-based soil OM estimation. By adjusting regression intercept values for each field, OM could be predicted using either a single sensor or image data layer. The final study consisted of validation of the active sensor algorithm developed by Solari (2006), identification of soil variables for MZ delineation, and the possible integration of MZ and active sensors for N application. Crop response (sensor measured sufficiency index and yield) had the highest correlation with soil optical reflectance readings in sandy fields and with apparent soil electrical conductivity in silt loam fields with eroded slopes. Therefore, using these soil variables to delineate MZ allowed characterization of spatial patterns in both in-season crop response (sufficiency index) and yield. Compared to uniform N application, integrating MZ and sensor-based N application resulted in substantial N savings (~40-120 kg ha-1) and increases in partial factor productivity (~13-75 kg grain (kg N applied)-1) for fine-textured soils with eroded slopes. However, for coarser texture soils the current sensor-based N application algorithm may require further calibration, and for fields with no spatial variability there appears to be no benefit to using the algorithm. Collectively, results from these studies show promise for integrating active sensor-based N application and static soil-based MZ to increase NUE and economic return for producers over current N management strategies, but further research is needed to explore how best to integrate these two N management strategies.
2009-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/3
https://digitalcommons.unl.edu/context/agronhortdiss/article/1002/viewcontent/dissertation.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
nitrogen
corn
active sensors
management zones
Agronomy and Crop Sciences
Plant Sciences
Soil Science
oai:digitalcommons.unl.edu:agronhortdiss-1003
2009-12-04T18:29:39Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Demographics and Habitat Selection for the Western Meadowlark (Sturnella neglecta) in the Nebraska Sandhills
Giovanni, Matthew D
The prairie ecosystems of the Great Plains region in North America have largely been replaced and fragmented with industrial agriculture and invasive herbaceous and woody plant species. The concurrent and large-scale suppression of wildfire and elimination of grazing by native ungulates may have further decreased the availability and quality of habitat for wildlife. Indeed, 2004 estimates indicate only 30% of historic grasslands in the Great Plains still exist, while the trends of decreased land area enrolled in the Conservation Reserve Program and increased land area in commercial agriculture indicate continued loss of habitat. This decrease in habitat availability continues to cause population declines for most grassland bird species in North America. The Nebraska Sandhills (Sandhills) region is the largest continuous mixed-grass prairie system remaining in North America, and is almost exclusively managed for cattle production with rotational grazing and wild-hay supplementation. The Sandhills are also, however, subject to increasing demands of natural resources while biological data for management and conservation planning is minimal at best. The Western Meadowlark (Sturnella neglecta) is broadly distributed across the temperate grasslands of central and western North America, but long-term abundance data indicate populations are declining across Nebraska and most of the species’ breeding range. The Sandhills are a potential population source for grassland bird species breeding elsewhere in fragmented, lower-quality habitat, but information on the demographic responses of species to land management in the Sandhills is mostly nonexistent. I sampled from a population of Western Meadowlarks in the central Sandhills from 2006-2008 to understand the relationships between breeding ecology, vegetation structure, and associated land management. Specifically, I report and discuss 1) selection of nest-site habitat by adults as a function of vegetation variables, 2) nest survival as a function of vegetation, researcher-effect, and temporal variables, 3) selection of habitat by fledglings as a function of vegetation variables, and survival of fledglings as a function of climate and temporal variables. Advisors: Larkin A. Powell and Walter H. Schacht
2009-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/4
https://digitalcommons.unl.edu/context/agronhortdiss/article/1003/viewcontent/Dissertation__Giovanni.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Biology
Plant Sciences
Population Biology
oai:digitalcommons.unl.edu:agronhortdiss-1006
2010-02-15T17:52:57Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
GENETIC DIVERSITY OF WHEAT CULTIVARS FROM TURKEY AND U.S. GREAT PLAINS
Auvuchanon, Anyamanee
Genetic diversity of wheat cultivars from Turkey and the Great Plains was studied under the hypothesis ‘Turkey’ wheat originated from Turkey and is the original hard red winter wheat landrace in the Great Plains. Wheat cultivars in Turkey and the Great Plains were selected for adaptation in two countries which were similar in climate. Twenty-two Turkish and twenty-three Great Plains wheat cultivars were selected for this study using SSR markers, agronomic, and end-use quality traits data. Wheat cultivars were clustered into five groups based on SSR markers and the clustering largely followed their countries of origin and pedigree. Modern Great Plains wheat cultivars diverged from Turkey wheat and historic Great Plains wheat cultivars. Although cultivars from one gene pool were predominant in each cluster, cultivars from another gene pool were also present indicating genetic similarity. Field experiments were conducted in six environments in Nebraska. The cultivars and cultivar by environment interactions for nine agronomic and four end-use quality traits were significant. Most Turkish wheat cultivars were injured by the Nebraska winter; hence showed lower grain yields. Great Plains wheat cultivars diverged from Turkish wheat cultivars due to breeding for adaptation based on agronomic traits. Turkish and U.S. wheat cultivars clustered together for end-use quality traits indicating similar selection criteria. Cluster analysis based on agronomic and end-use quality combination indicated that wheat cultivars from two countries had separated. The original Great Plains wheat cultivars (Turkey and Kharkof) were clustered separately from modern Great Plains wheat cultivars by both SSR and combination of agronomic and end-use quality data. Our results suggested that breeding programs in both countries improved wheat cultivars for specific environment as the genetic diversity based on agronomic traits; nevertheless, SSR markers indicated that 130 years after the introduction of Turkey wheat, much of the genetic background of two wheat groups has been maintained. The better adapted Turkish wheat cultivars in Nebraska were Karasu-90, Alpaslan, Lancer, Dogu-88, Harmankaya, and Yildirim which can be used as parents.
2010-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/5
https://digitalcommons.unl.edu/context/agronhortdiss/article/1006/viewcontent/GENETIC_DIVERSITY_OF_WHEAT_CULTIVARS_FROM__TURKEY_AND_US_GREAT_PLAINS.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Genetic Diversity
SSR
Great Plains wheat
Turkish wheat
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1007
2010-04-21T16:20:44Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
GRAIN YIELD AND YIELD-RELATED QTL VALIDATION USING RECIPROCAL RECOMBINANT INBRED CHROMOSOME LINES IN WHEAT
Mengistu, Neway C
Grain yield and yield-related traits are the most important economic factors for bread wheat (Triticum aestivum L.) improvement. Grain yield (GYLD) and yield-related quantitative trait loci (QTLs) were previously identified by using a population of recombinant inbred chromosome lines (RICLs) developed from cultivar ‘Cheyenne’ (CNN) and its substitution line CNN(WI3A), where the 3A chromosome of cultivar ‘Wichita’ (WI) was substituted for the CNN chromosome 3A. The objectives of this study were to identify and validate GYLD and yield-related QTLs previously identified in CNN(RICLs-3A) studies by using the mirror population WI(RICLs-3A), where chromosome 3A of CNN and WI were now recombined in the WI background. A population of 90 F1-derived doubled haploid lines derived from WI x WI(CNN3A) was used to evaluate GYLD, 1000-kernel weight (TKW), kernels per spike (KPS), kernels per square meter (KPSM), spikes per square meter (SPSM), grain volume weight (GVW), anthesis date (AD), and plant height (PHT). The agronomic traits data were collected from replicated trials grown in six Nebraska environments from 2008 to 2009. Twelve QTLs associated with variation for GYLD, TKW, KPS, SPSM, GVW, AD, and PHT were detected. The phenotypic variance explained by these QTLs ranged from 12% for SPSM to 53% for GVWT. Most of the QTLs were co-localized in a cluster or closely linked into two regions of chromosome 3A. The major grain yield QTL (QGyld.neb.3A.1) detected in the combined analysis explained 19% of the phenotypic variance and the substitution of a CNN allele for a WI allele decreased grain yield by 87 kg ha-1. Using a different genetic background, this study detected most of the GYLD and yield-related QTLs reported in previous RICLs-3A mapping studies on chromosome 3A of winter wheat evaluated in Nebraska. The identified QTLs or genomic regions associated with GYLD and yield-related traits will be a useful tool for future marker assisted breeding in improving the yield potential of bread wheat. Additional work such as fine-mapping and cloning the QTLs for grain yield and yield-related traits will facilitate utilization of these traits in breeding programs.
2010-04-21T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/6
https://digitalcommons.unl.edu/context/agronhortdiss/article/1007/viewcontent/Dissertation_Neway_20th_April_2010.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Wheat
QTL Validation
Recombinant Inbred Chromosome Lines
Nebraska
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1008
2016-09-01T19:33:30Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Effect of Grazing System on Livestock Performance, Botanical Composition, and Standing Crop in the Nebraska Sandhills
Stephenson, Mitchell B
A 10-year study compared a 4-pasture deferred-rotation (DR) grazing system with an 8-pasture short duration grazing (SDG) system at the Barta Brothers Ranch near Rose, NE to determine differences in livestock performance, botanical composition, and standing crop. Pastures were grazed by 50 to100 cow-calf pairs with both single (DR system) and multiple (SDG system) grazing periods from 15 May to 15 October. Livestock performance data were collected from spayed heifers substituted into each grazing system during the last 3 years of the study. Botanical composition was collected on 275 frequency of occurrence transects in 1998, 2003, and 2008. Standing crop data were collected biannually within 240 grazing exclosures placed at 4 topographic positions from 2000 to 2008. Average daily gain of the spayed heifers (0.84 kg∙day-1) did not differ between grazing systems and years. The DR grazing system had minimal increases of standing crop and frequency of occurrence of desirable plant species. Standing crop and frequency of occurrence were more affected by topographic position and year than by grazing system treatments. Effect of timing of grazing on subsequent-year standing crop was also determined with the DR and SDG grazing systems. Standing crop data were used to determine effect of time of grazing on plant functional groups. Subsequent-year warm-season grass standing crop with the DR system was lowest when grazing occurred from 21 July to 31 August. Cool- season grass and forb standing crop was most affected when grazing took place in mid-May, mid-June, and late-August within the SDG system Browse production tended to be lower when grazing occurred early in the grazing season for both grazing systems. Grazing during times when standing crop is most limited in subsequent-years should not take place in consecutive years on pastures in either system unless specific management objectives are trying to be obtained.
2010-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/7
https://digitalcommons.unl.edu/context/agronhortdiss/article/1008/viewcontent/Thesis__Mitch_Stephenson_.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
grazing system
short duration grazing
deferred-rotation grazing
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1009
2010-07-26T15:59:58Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
QUANTITATIVE TRAIT LOCI FOR AGRONOMIC AND END-USE QUALITY PERFORMANCE AND THE EFFECT OF SOILBORNE WHEAT MOSAIC VIRUS IN A HARD WINTER WHEAT POPULATION IN NEBRASKA
Crowley, Nicholas A
To better understand agronomic and end-use quality in wheat (Triticum aestivum L.) we developed a population containing 154 F6:8 recombinant inbred lines (RILs) from the cross TAM107-R7/Arlin. The parental lines and RILs were phenotyped at six environments in Nebraska and differed for resistance to Wheat soilborne mosaic virus (WSBMV), morphological, agronomic, and end-use quality traits. Additionally, a 2300 cM genome-wide linkage map was created for quantitative trait loci (QTL) analysis. Based on our results across multiple environments, the best RILs could be used for cultivar improvement. The population and marker data are publicly available for interested researchers for future research.
The population was used to determine the effect of WSBMV on agronomic and end-use quality and for the mapping of a resistance locus. Results from two infected environments showed that all but two agronomic traits were significantly affected by the disease. Specifically, the disease reduced grain yield by 30% of susceptible RILs and they flowered 5 d later and were 11 cm shorter. End-use quality traits were not negatively affected but flour protein content was increased in susceptible RILs. The resistance locus SbmTmr1 mapped to 27.1 cM near marker wPt-5870 on chromosome 5DL using ELISA data. Finally, we investigated how WSBMV affected QTL detection in the population. QTLs were mapped at two WSBMV infected environments, four uninfected environments, and in the resistant and susceptible RIL subpopulations in the infected environments. Fifty-two significant (LOD≥3) QTLs were mapped in RILs at uninfected environments. Many of the QTLs were pleiotropic or closely linked at 6 chromosomal regions. Forty-seven QTLs were mapped in RILs at WSBMV infected environments. Comparisons between uninfected and infected environments identified 20 common QTLs and 21 environmentally specific QTLs. Finally, 24 QTLs were determined to be affected by WSBMV by comparing the subpopulations in QTL analyses within the same environment. The comparisons were statistically validated using marker by disease interactions. These results showed that QTLs can be affected by WSBMV and careful interpretation of QTL results is needed where biotic stresses are present. Finally, beneficial QTLs not affected by WSBMV or the environment are candidates for marker-assisted selection.
2010-07-26T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/8
https://digitalcommons.unl.edu/context/agronhortdiss/article/1009/viewcontent/Nick_Crowley_Dissertation_Final_version.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agronomy and Crop Sciences
Genetics
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1010
2010-07-28T13:55:20Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Linkage & Selective Mapping and QTL Analysis in a Harosoy x Clark population of 300 RILs
Hwang, Sadal
Four of the 12 major Glycine max ancestors of all modern elite U.S.A. soybean cultivars were the grandparents of Harosoy and Clark, so a Harosoy x Clark population would include some of that genetic diversity. A mating of eight Harosoy and eight Clark plants generated eight F1 plants. The eight F1:2 families were advanced via a plant-to-row selfing method to produce 300 F6-derived RILs that were genotyped with 266 SSR, 481 SNP, and 4 classical markers. SNPs were genotyped with the Illumina 1536-SNP assay. Three linkage maps, SSR, SNP, and SSR-SNP, were constructed with a genotyping error of < 1 %. Each map was compared with the published soybean consensus map. The best subset of 94 RILs for a high-resolution framework (joint) map was selected based on the expected bin length statistic computed with MapPop. The QTLs of seven traits measured in a 2-year replicated performance trial of the 300 RILs were identified using composite interval mapping (CIM) and multiple-interval mapping (MIM). QTL x Year effects in multiple trait analysis were compared with results of multiple-interval mapping. QTL x QTL effects were identified in MIM.
2010-08-13T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/9
https://digitalcommons.unl.edu/context/agronhortdiss/article/1010/viewcontent/Dissertation__Sadal_Hwang_.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
QTL
RIL
SSR
SNP
Bin
CIM
and MIM
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1011
2016-11-09T21:44:49Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Yield potential and resource-use efficiency of maize systems in the western U.S. Corn Belt
Grassini, Patricio
Maize demand for food, livestock feed, and biofuel is expected to increase substantially. The Western U.S. Corn Belt accounts for 23% of U.S. maize production, and irrigated maize accounts for 43 and 58% of maize land area and total production, respectively, in this region. The most sensitive parameters (yield potential [YP], water-limited yield potential [YP-W], yield gap between actual yield and YP, and resource-use efficiency) governing performance of maize systems in the region are lacking. A simulation model was used to quantify YP under irrigated and rainfed conditions based on weather data, soil properties, and crop management at 18 locations. In a separate study, 5-year soil water data measured in central Nebraska were used to analyze soil water recharge during the non-growing season because soil water content at sowing is a critical component of water supply available for summer crops. On-farm data, including yield, irrigation, and nitrogen (N) rate for 777 field-years, was used to quantify size of yield gaps and evaluate resource-use efficiency. Simulated average YP and YP-W were 14.4 and 8.3 Mg ha-1, respectively. Geospatial variation of YP was associated with solar radiation and temperature during post-anthesis phase while variation in water-limited yield was linked to the longitudinal variation in seasonal rainfall and evaporative demand. Analysis of soil water recharge indicates that 80% of variation in soil water content at sowing can be explained by precipitation during non-growing season and residual soil water at end of previous growing season. A linear relationship between YP-W and water supply (slope: 19.3 kg ha-1 mm-1; x-intercept: 100 mm) can be used as a benchmark to diagnose and improve farmer’s water productivity (WP; kg grain per unit of water supply). Evaluation of data from farmer’s fields provides proof-of-concept and helps identify management constraints to high levels of productivity and resource-use efficiency. On average, actual yields of irrigated maize systems were 11% below YP. WP and N-fertilizer use efficiency (NUE) were high despite application of large amounts of irrigation water and N fertilizer (14 kg grain mm-1 water supply and 71 kg grain kg-1 N fertilizer). While there is limited scope for substantial increases in actual average yields, WP and NUE can be further increased by: (1) switching surface to pivot systems, (2) using conservation instead of conventional tillage systems in soybean-maize rotations, (3) implementation of irrigation schedules based on crop water requirements, and (4) better N fertilizer management.
2010-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/10
https://digitalcommons.unl.edu/context/agronhortdiss/article/1011/viewcontent/2010_07_26_Patricio_Grassini_PhD_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
maize
corn
corn belt
yield potential
yield gap
resource-use efficiency
water productivity
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1012
2010-07-28T16:03:58Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Genetic Mapping of Quantitative Trait Loci Associated with Bioenergy Traits, and The Assessment of Genetic Variability in Sweet Sorghum (Sorghum bicolor (L.). Moench)
Lekgari, Aatshwaelwe Lekgari
Sweet sorghum, a botanical variety of sorghum is a potential source of bioenergy because high sugar levels accumulate in its stalks. The objectives of this study were to explore the global diversity of sweet sorghum germplasm, and map the genomic regions that are associated with bioenergy traits. In assessing diversity, 142 sweet sorghum accessions were evaluated with three marker types (SSR, SRAP, and morphological markers) to determine the degree of relatedness among the accessions. The traits measured (anthesis date [AD], plant height [PH], biomass yield [BY], and moisture content [MC]) were all significantly different (P<0.05) among accessions. Morphological marker clustered the accessions into five groups based on PH, MC and AD. The three traits accounted for 92.5% of the variation. There were four and five groups based on SRAP and SSR data respectively classifying accessions mainly on their origin or breeding history. The observed difference between SSR and SRAP based clusters could be attributed to the difference in marker type. SSRs amplify any region of the genome whereas SRAP amplify the open reading frames and promoter regions. Comparing the three marker-type clusters, the markers complimented each other in grouping accessions and would be valuable in assisting breeders to select appropriate lines for crossing. In evaluating QTLs that are associated with bioenergy traits, 165 recombinant inbred lines (RILs) were planted at four environments in Nebraska. A genetic linkage map constructed spanned a length of 1541.3 cM, and generated 18 linkage groups that aligned to the 10 sorghum chromosomes. Fourteen QTLs (6 for brix, 3 for BY, 2 each for AD and MC, and 1 for PH) were mapped. QTLs for the traits that were significantly correlated, colocalized in two clusters on linkage group Sbi01b. Both parents contributed beneficial alleles for most of traits measured, supporting the transgressive segregation in this population. Additional work is needed on exploiting the usefulness of chromosome 1 in breeding sorghum for bioenergy.
2010-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/11
https://digitalcommons.unl.edu/context/agronhortdiss/article/1012/viewcontent/dissertation_draft_Final2.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
sorghum
QTL
bioenergy
diversity
accessions
RILs
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1013
2010-07-29T13:51:42Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Xenia Effects on Quality of Maize Female Inbred in Production of Hybrid Seeds
Castañeda, Leandro
In Maize (Zea maize L.), cost of hybrid seed production is directly related to the yield and quality of seed obtained per hectare of female parent. It is also important to consider the effects that a male parent can exert on the development of hybrid seed in the female parent. This effect is known as xenia. The objectives of this study were to evaluate xenia effects on 1) yield as 80K units, 2) germination of the hybrid seed and 3) susceptibility of the hybrid seed to mechanical damage. One female inbred and four male inbred lines were selected from a parent list of hybrids. The experiment was designed to allow individual cross pollination between each male inbred and the female inbred line. For use as a control, the female inbred was allowed to self pollinate. Experiments were conducted in Illinois and Iowa during 2008 and 2009 and in Nebraska during 2009. A significant inbred effect was detected on yield as 80k (α=0.001). The selfed female and pollination with male inbred B resulted in lower yields of hybrid seed. For germination, a significant inbred effect was detected (α=0.001), but was due to lower germination percentage of seed produced on the selfed female. All hybrid combinations resulted in higher germination percentages with no significant differences among hybrids. The inbred x mechanical damage interaction was significant (P=0.04) for effects on cold saturated soil germination tests. Use of inbred B resulted in a two-percentage-point reduction in cold germination when treated with the impact simulator. In a maize seed company, the production research group provides yield estimates for production of new hybrid combinations. Results from this study indicate that using only the female inbred yield may provide inaccurate estimates. Therefore to improve yield estimation, experiments should be designed to include male inbreds. Male inbreds can also impart a negative effect to the hybrid seed on tolerance to mechanical damage, thus lowering quality and increasing seed discard. When testing for hybrid seed germination, there is no need to consider distinct hybrid combinations. Female inbreds can be grown in open-pollinated fields to avoid loss of vigor observed with selfing.
Advisor: George Graef
2010-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/12
https://digitalcommons.unl.edu/context/agronhortdiss/article/1013/viewcontent/Xenia_Effects_on_Quality_of_Maize_Female_Inbreds_in_Production_of_Hybrid_Seed_manuscript.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Xenia
Maize
Hybrid seed
Production
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1014
2010-09-23T21:46:41Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Ability of <i> Plectranthus </i> spp to Re-green After Nitrogen Deficiency
Chahal, Jazbaat K
Nitrogen is the most important nutrient for plant growth and development. This is due to the reason that nitrogen is a key constituent of amino acids, nucleic acids, lipids and chlorophyll. Stress caused by nitrogen deficiency has a large impact on plant growth and development. In most plants, older leaves become chlorotic and eventually fall off if nitrogen stress is not relieved. Chlorophyll concentration is important to determine the nitrogen concentration in a plant as nitrogen is a constituent element of chlorophyll and also of various proteins that are a part of the photosynthetic apparatus. Cytokinins are said to mediate nutrient information status in plants, especially that of nitrogen. The purpose of this research was to measure chlorophyll and cytokinin concentrations to compare the response of Plectranthus parviflorus and Plectranthus ambiguus to nitrogen stress as well as to sufficient nitrogen and to determine if cytokinins were the reason behind the difference in their response. It would be expected that P.parviflorus would have higher concentration of cytokinins at 0 N as this plant does not lose its leaves and re-greens upon re-introduction of nitrogen. Both the species were grown in hydroponics for 6 weeks for each experiment. The plants received either 0 mg/L N or 150 mg/L N for week 1 to 3 and then there was a switch of treatments with plants receiving either 0-0 mg/L N, 0-150 mg/L N, 150-150 mg/L N or 150-0 mg/L N. Leaves were traced to determine leaf area and then assayed to determine chlorophyll and cytokinin concentration of the plants. At the end of the experiment plants were harvested, dried in an oven and their dry weights were measured. The chlorophyll concentration in plants of both species receiving 0 mg/L N decreased while those receiving 150 mg/L N increased. Also when the plants were switched from 0 to 150 mg/L N they showed an increase in chlorophyll concentration in both species while those switched from 150 to 0 mg/L N showed a decline in their chlorophyll concentrations. Thus, in general, for both species chlorophyll concentration increased when sufficient nitrogen was given to plants while, it decreased when plants were grown under nitrogen stress. Plectranthus ambiguus always had a higher chlorophyll concentration than Plectranthus parviflorus throughout the experiment. Concentrations of the biological precursors, physiologically active and storage forms of cytokinin were lower in plants growing under 0 mg/L N while those plants growing under 150 mg/L N had higher concentrations. Thus when P.ambiguus plants receiving 0 mg/L N lost its leaves or when P.parviflorus plants receiving 0 mg/L N stopped its growth, all of these forms of cytokinins were present in low concentration in the plants. It was also observed that when during nitrogen stress P.ambiguus shed its leaves while P. parviflorus did not. Thus, there was no key difference in their respective cytokinin concentrations. It therefore can be concluded that the cytokinin concentration alone is not responsible for the difference in the response of these two species to nitrogen stress. Advisor: Ellen T. Paparozzi
2010-09-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/13
https://digitalcommons.unl.edu/context/agronhortdiss/article/1014/viewcontent/MS_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1015
2010-11-30T20:56:24Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Delaying Bud Break in ‘Edelweiss’ Grapevines to Avoid Spring Frost Injury by NAA and Vegetable Oil Applications
Qrunfleh, Issam M.
Delaying bud break is an approach to avoid spring frost damage. Field experiments were conducted during the winters of 2009 and 2010 at James Arthur Vineyards in Raymond, Nebraska to study the effect of spraying NAA and Amigo Oil on delaying bud break in ‘Edelweiss’ grapevines to avoid such damage. In 2009, the experiment consisted of five treatments: NAA (500, 750, and 1000 mg/l), oil applied at 10%, and the non-sprayed control. There were four application dates: January 6, February 3, March 3, and April 1. Bud break was evaluated throughout spring. During harvest, the number of clusters and weights were recorded. Berry samples were analyzed for pH, °Brix, and titratable acidity (TA). Pruning weights and number of clusters of the 2009 treated vines were recorded in March and August 2010, respectively. In 2010, NAA concentrations were 500, 1000, and 1500 mg/l, 10% oil, and the control. Application dates were: January 28, February 25, and March 25. Similarly to 2009, bud break was evaluated throughout spring, number of clusters and weights per vine were recorded, and berry samples were analyzed for the same parameters mentioned as in 2009.
A forcing solution experiment was conducted on ‘Edelweiss’ canes collected on the same dates as the field experiments. For each date, 20 canes were headed back to the first five buds, then cut into five single-bud cuttings and the bases immersed in forcing solution. The same treatments as used in the field experiments were applied by adding one drop on each bud. Days to bud break and shoot length one week after bud break were recorded.
In the 2009 field experiment, oil and NAA at 1000 mg/l significantly delayed bud break 2-6 days compared to the control. In 2010, oil applications significantly delayed bud break 8-12 days compared to the control and no significant differences were found between NAA at 1500 and 1000 mg/l. In both years, treatments had no significant effects on yields, cluster weights, berry weights, °Brix, pH, and TA. The forcing solution experiment showed a month, position, and treatment interaction regarding bud break delay in both years. No treatment effects were found regarding shoot length.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/14
https://digitalcommons.unl.edu/context/agronhortdiss/article/1015/viewcontent/Diss_Complete.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Horticulture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1016
2010-11-30T22:46:57Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
IDENTIFICATION OF SOURCES OF RHIZOCTONIA ROOT ROT RESISTANCE IN COMMON BEAN AND MAPPING A NEW SOURCE OF BEAN RUST RESISTANCE FROM THE TERTIARY GENE POOL OF COMMON BEAN
Peña-Perdomo, Pamela A
An efficient screening method was developed and used to identify bean lines resistant to Rhizoctonia Root Rot caused by Rhizoctonia solani Kuhn. Two sets of 163 and 111 lines previously evaluated for drought tolerance at Mitchell, NE and Isabela, PR were evaluated for Rhizoctonia Root Rot resistance under greenhouse conditions. This root rot data was also correlated with yield under drought stress and non stress conditions. In the first set of lines the rhizoctonia mean score ranged from 1.7 to 3.9; and in the second set the rhizoctonia mean score was between 2.6 and 5.7. There was no significant correlation between drought tolerance and Rhizoctonia Root Rot resistance, but there were drought tolerant lines that also had Rhizoctonia Root Rot resistance. Lines with both traits can be used as parents in breeding programs looking for improvement of both drought tolerance and Rhizoctonia Root Rot resistance in dry beans. A new source of resistance of Common Bean Rust from the tertiary gene pool of common beans was mapped. Two linkage maps from RILs of a reciprocal interspecific cross between Phaseolus acutifolius (G40022) and Phaseolus parvifolius (G40186) (AP and PA RIL population) were constructed. A total cumulative map length for the AP population was 746 cM, with an average chromosome length of 62.2 cM and an average distance between markers of 11.3 cM. In the PA RIL population, the total cumulative map length was 920.8 cM, with an average chromosome length of 61.4 cM; and the average distance between markers distributed in this map was 11.3 cM. The QTL analyses revealed a putative QTL located on the linkage group LG5 of the AP RIL population was located at 67.7 cM, and it had a LOD 20.1. More molecular markers are needed to saturate the map and be able to identify a marker at least at 5 cM from the QTL.
2010-11-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/15
https://digitalcommons.unl.edu/context/agronhortdiss/article/1016/viewcontent/Pamela_Pena_MSThesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Rhizoctonia root rot
Common bean rust
QTL mapping
Plant Breeding and Genetics
Plant Pathology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1018
2010-12-02T02:30:16Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MICROPROPAGATION AND ACCLIMATIZATION OF 'NORTON' GRAPEVINE (<i>VITIS AESTIVALIS</i>)
Bigger, Brant B
Propagation of the Vitis aestivalis cultivar 'Norton‘ (syn='Cynthiana‘) through traditional woody cuttings has been difficult. Rooting of woody cuttings has been a major hindrance in propagating this cultivar and providing enough plants to meet grower needs. In vitro propagation offers another method of increasing plant material. Cultures were established and maintained on Murashige and Skoog (MS) medium supplemented with 4 M 6-benzyladenine (BA) and thiamine at 0.5 mg•L-1 and solidified with Difco-Bacto agar at 7.5 g•L-1. The objectives of this study were to determine optimal methods for in vitro production and ex vitro establishment of 'Norton‘ plantlets. A factorial treatment with 4 concentrations of BA (0, 2, 4 & 8 µM) and 2 concentrations of naphthaleneacetic acid (NAA) (0 & 0.5 µM) was used for the multiplication study. Plantlets were acclimatized to ex vitro conditions without in vitro rooting. Plantlets were rooted ex vitro either with or without a 1000 ppm (0.1%) indolebutric acid (IBA) basal dip for 5 seconds. Auxin did not have a significant effect on explant growth or plantlet rooting. This demonstrates an improved method of in vitro propagation and acclimatization for efficient multiplication of 'Norton‘ grapevines. Advisor: Paul E. Read
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/16
https://digitalcommons.unl.edu/context/agronhortdiss/article/1018/viewcontent/Thesis_Final.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Fruit Science
Horticulture
Laboratory and Basic Science Research
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1019
2010-12-02T03:56:26Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
EVALUATION OF NOVEL INPUT OUTPUT TRAITS IN SORGHUM THROUGH BIOTECHNOLOGY
Mall, Tejinder K.
Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop world-wide as well as an important source of feed, fiber and biofuel. It is a C4 plant and is well adapted to environments subject to high temperature and water limitation. Despite these agronomic qualities, it suffers from limitations of sensitivity to low temperature and the grain has drawbacks in relation to functionality and digestibility. The objectives of this study are: 1. To promote seed germination at low temperature and to enhance the seedling cold tolerance. 2. To enhance the grain digestibility and functionality. In an attempt to augment cold tolerance, we introduced the glycine rich RNA binding protein gene atRZ-1a from Arabidopsis, Bcl-2 mRNA sequence 725-1428 representing the 3’ non coding region of the gene from humans and rice Ca-dependent protein kinase 7 (OsCDPK7), all of which are known to improve the cold tolerance of plants. None of these genes resulted in the improvement of cold tolerance in sorghum. On the other hand ectopic expression of OsCDPK7 in sorghum led to local lesions formation in leaves. The data generated from this study indicated that constitutive modulation of the CDPK signal transduction pathway in sorghum can trigger a localized cell death response. Further we targeted improving the grain digestibility and functionality. To accomplish this objective we introduced the wheat high-molecular-weight glutenin subunits (HMW-GS) into sorghum which are known to have significant impact on flour quality. Transgenic events expressing HMW-GS showed improvement in protein digestibility of the uncooked ground grain. In separate complementary set of sorghum transformations we introduced genetic cassettes designed to specifically down-regulate the accumulation of the sorghum alpha and gamma kafirins. Down-regulation of alpha kafirin showed presence of distorted protein bodies in the transgenic seed. The long-term goal of this project is to stack the HMW-GS trait with the modulated kafirins events, as a means to address both end-use functionality and digestibility.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/17
https://digitalcommons.unl.edu/context/agronhortdiss/article/1019/viewcontent/Thesis_18.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
sorghum
cold tolerance
cdpk7
kafirin
transformation
high molecular weight glutenin subunits
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1020
2010-12-02T20:28:21Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
DETECTION OF SOYBEAN SEED PROTEIN QTLS USING SELECTIVE GENOTYPING
Phansak, Piyaporn
A quantitative trait locus (QTL) is a statically defined location of a gene governing that trait. QTL identification is the first step towards using marker-assisted selection (MAS) to introgress desirable QTL alleles into elite high-yield cultivars. Hundreds of high protein plant introductions (PIs) exist in the USDA germplasm collection and are a source of high protein alleles. Although 86 protein QTLs are currently listed in SoyBase, many are likely repeat discoveries of the same QTL(s), given the typical +/- 10 cM confidence intervals associated with QTL positions. Six germplasm accessions of maturity groups (MGs) II to IV that exhibited high seed protein (480 g kg-1 or more) were mated to a high-yielding cultivars of the same MG that exhibited normal seed protein (420 g kg-1 or less) to generate six F2 populations. A total of 240 individual F2 plants in each population produced F2:3 seed progenies that were phenotyped for seed protein content. Selective genotyping, or phenotypic tail analysis, was used to genotype only those F2:3 progenies occupying the lowest decile and the highest decile. A 1536-SNP locus assay chip was used for the genotyping. In the six mapping populations, eight protein QTLs with LOD scores greater than 3.0 were detected and mapped on five linkage groups using R/qtl. Significant QTLs on LG-C2 (Chromosome 6), LG-O (10), LG-B2 (14), LG-E (15), and LG-I (20) were detected. A review of the currently listed QTLs in Soybase (2010) indicated that no seed protein QTLs had been previously reported on LG-O (10). The new seed protein QTL discovered in this study in populations 1076, 1121, and 1122 is located on LG-O (10) near the two adjacent markers S19004 and S15265, and has an additive effect of 9.6, 7.9, and 6.5 g kg-1 greater seed protein, respectively. For improving the seed protein content in high yielding soybean cultivars, the accessions PI 437112A (1076), PI 398672 (1121), and PI 360843 (1122), which posses the high protein allele at this new LG-O (10) protein QTL, may be useful to soybean breeders.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/18
https://digitalcommons.unl.edu/context/agronhortdiss/article/1020/viewcontent/Final_Dissertation_Piyaporn_Phansak.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Selective genotyping
Seed protein QTLs
Quantitative trait lucus
Soybean
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1021
2010-12-03T18:27:43Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
FUSARIUM HEAD BLIGHT: WINTER WHEAT CULTIVAR RESPONSES AND CHARACTERIZATION OF PATHOGEN ISOLATES
Hernandez Nopsa, John Fredy
Fusarium head blight (FHB) is a destructive disease of wheat (Triticum aestivum L). FHB reduces yield and grain quality and causes accumulation of the mycotoxin deoxynivalenol (DON) in grain. Cultivar resistance is one of the most effective management strategies for FHB. Experiments were conducted to 1) identify winter wheat cultivars with resistance to FHB and DON accumulation, 2) determine the effect of winter wheat cultivar on the relationship between FHB and DON concentration, and 3) identify the major species of Fusarium causing FHB in Nebraska and characterize its isolates. Differences (P ≤ 0.05) were detected among cultivars in FHB index, Fusarium-damaged kernels, DON, and yield. The cultivars Alliance, Harry, Hondo, Infinity CL, and Overland were moderately resistant to FHB and DON accumulation. Harry was resistant to FHB but susceptible to DON accumulation. Overley, Jagalene, Wesley, and 2137 were susceptible to FHB and DON accumulation. The relationship between FHB severity and DON concentration was linear and positive regardless of cultivar. However, regression slopes indicated that this relationship was cultivar dependent. Forty of 41 isolates of Fusarium obtained from infected winter wheat kernels in grain collected from elevators and fields in Nebraska were identified by polymerase chain reaction (PCR) morphological characteristics as Fusarium graminearum Schwabe (Teleomorph: Gibberella zeae (Schwein.) Petch). Seventeen selected isolates differed (P ≤ 0.05) in the number and size of perithecial units (single perithecium or clusters of perithecia) produced in culture and seven selected isolates differed (P ≤ 0.05) in aggressiveness on wheat spikes and detached leaves. Based on aggressiveness on wheat spikes, the seven isolates were grouped into three categories: 1) highly aggressive (isolates 103, 110, and 119), 2) moderately aggressive (isolates 91 and 98), and 3) weakly aggressive (isolates 90 and 97).
2010-11-23T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/19
https://digitalcommons.unl.edu/context/agronhortdiss/article/1021/viewcontent/NOPSA_PhD_thesis_FINAL.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
FHB
Fusarium head blight
Scab
Wheat
Fusarium graminearum
cultivar
characterization
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Pathology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1022
2010-12-06T18:10:44Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
THE IMPACT OF LONG-TERM TILLAGE, CROP ROTATION AND N APPLICATION ON SOIL CARBON SEQUESTRATION
Martellotto, Agustin
Soil organic carbon (SOC) stock is controlled by many factors, but for given conditions it is the long term summation of the balance between inputs and outputs. Management practices will alter this balance by affecting the system’s productivity and the speed of residue and soil organic matter decomposition. Given that annual changes in SOC are generally small, compared with the large and variable SOC background, long-term experiments, and soil samples taken at the start of experiments (archived samples) are necessary to determine SOC trends over time. Changes in SOC were analyzed for two long-term experiments; one an irrigated site at Mead, NE (1997) with continuous corn (CC) (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation) and 3 nitrogen (N) application rates (0, 100 and 300 kg ha-1); and the other a rainfed site at Concord, NE, (1985) with three tillage treatments (no-till, NT, disk, DK, and moldboard plow, MP), two crop sequences (CC and CS) and three N application rates (0, 80 and 160 kg ha-1). Soil samples taken at early stages of the experiments were used as a benchmark to analyze carbon trends over time. Results showed that in spite of considerable differences, C inputs did not affect changes in SOC. Nitrogen fertilizer application resulted in a 3% increase in SOC, but required 24 years to generate detectable differences in the surface 400 kg of soil m-2. Over the last 12 years, MP lost 1.52 ±0.4 kg of C m-2 while NT lost 0.73 ±0.4 and DK lost 0.76 ±0.4 kg of C m-2 in the 1200 kg of soil m-2 profile. None of the evaluated treatments under the conditions of these experiments were able to sequester atmospheric C since all lost SOC over time. The use of archived samples made possible the determination of the rate of SOC change over time, and allowed an accounting for natural soil variability.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/20
https://digitalcommons.unl.edu/context/agronhortdiss/article/1022/viewcontent/Martellotto_MS_thesis2.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
soil organic carbon
carbon sequestration
tillage
crop rotation
archived samples
SOC
long-term effects
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1023
2010-12-15T23:03:42Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Estimating Maize Grain Yield From Crop Biophysical Parameters Using Remote Sensing
Guindin-Garcia, Noemi
The overall objective of this investigation was to develop a robust technique to predict maize (Zea mays L.) grain yield that could be applied at a regional level using remote sensing with or without a simple crop growth simulation model. This study evaluated capabilities and limitations of the Moderate Resolution Imaging Spectroradiometer (MODIS) Vegetation Index 250-m and MODIS surface reflectance 500-m products to track and retrieve information over maize fields. Results demonstrated the feasibility of using MODIS data to estimate maize green leaf area index (LAIg). Estimates of maize LAIg obtained from Wide Dynamic Range Vegetation Index using data retrieved from MODIS 250-m products (e.g. MOD13Q1) can be incorporated in crop simulation models to improve LAIg simulations by the Muchow-Sinclair-Bennet (MSB) model reducing the RMSE of LAIg simulations for all years of study under irrigation. However, more accurate estimates of LAIg did not necessarily imply better final yield (FY) predictions in the MSB maize model. The approach of incorporating better LAIg estimates into crop simulation models may not offer a panacea for problem solving; this approach is limited in its ability to simulate other factors influencing crop yields. On the other hand, the approach of relating key crop biophysical parameters at the optimum stage with maize grain final yields is a robust technique to early FY estimation over large areas. Results suggest that estimates of LAIg obtained during the mid-grain filling period can used to detect variability of maize grain yield and this technique offers a rapid and accurate (RMSE < 900 kg ha-1) method to detect FY at county level using MODIS 250-m products.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/21
https://digitalcommons.unl.edu/context/agronhortdiss/article/1023/viewcontent/Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
MODIS
temporal resolution
vegetation indices
maize
green leaf area index
crop simulation models
maize yield
Agricultural Science
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1025
2017-11-14T16:57:38Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Evaluating commercially available diagnostic tests for the detection of <i>Clavibacter michiganensis</i> subsp. <i>nebraskensis</i>, cause of Goss's bacterial wilt and leaf blight in corn
Korus, Kevin A
Goss’s wilt and blight of corn, caused by the bacterium Clavibacter michiganensis (Cm) subsp. nebraskensis (Cmn), is currently diagnosed by symptom identification and successful isolation onto CNS selective medium. An ELISA test kit and ImmunoStrips (Agdia®) specific to Cm michiganensis (Cmm) reportedly give a cross-reaction with Cm subspecies. Also, the GEN III OmniLog Identification system (Biolog Inc., Hayward, CA) is said to provide accurate identification of Cm subspecies. These tests would provide a quick and inexpensive method for diagnosis of Cmn but have not been previously validated. ELISA test kits were provided by Agdia for the detection of Cmm, Cm tessellarius (Cmt), and Cm sepedonicus (Cms) as well as ImmunoStrips developed for the detection of Cmm. Also, an ELISA test kit (Neogen®) specific to Cmn was included in the study. For each ELISA and ImmunoStrip, 15 strains of Cmn, 5 Cmm, 5 Cmt, 4 Cms, 3 Cmi and 40 symptomatic leaf samples submitted from widely dispersed commercial corn fields to the UNL Plant & Pest Diagnostic Clinic were tested. The ImmunoStrips were tested with an additional 29 Cmn isolates as well as 17 bacterial isolates outside the genus Clavibacter. All ELISA test kits, except those for Cms, consistently gave positive results for all 40 infected leaf samples. Cmn was confirmed in the leaf samples with Koch’s postulates. When testing cultures, the Cmn, Cmm, and Cmt ELISAs gave consistent positive results. The Cms ELISA gave consistent negative results. ImmunoStrips for Cmm consistently tested positive for cultures of all the Cm subspecies and plant samples infected with Cmn and negative results for those bacteria outside the genus Clavibacter. ELISAs using antibodies specific to Cmm, Cmn and Cmt and ImmunoStrips using antibodies specific to Cmm can be used reliably when testing for the presence of Cmn. Further additions to the GEN III OmniLog ID system may be needed to provide consistent identifications of gram-positive coryneform phytopathogenic bacteria, namely those belonging to the genus Clavibacter
2011-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/22
https://digitalcommons.unl.edu/context/agronhortdiss/article/1025/viewcontent/THESIS_TOTAL_4.6.11.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Clavibacter
Goss's
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1026
2011-04-14T21:38:15Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Characterizing the Chemoprevention Potential of Amenity Grass Phenolic Extracts <i>In Vitro</i> and the Corresponding Nutraceutical Targets within HepG2 Carcinoma Cells
Wegner, Casey J
This research has revealed significant chemopreventive potential belonging to the planet’s most renewable and abundant plant source: amenity grasses. The characterization results from Chapter 1 demonstrated the potential chemoprevention attributes of supina bluegrass and bermudagrass crude extracts linked to the extensive phenolic acid profiles of these amenity grasses. In contrast to cereals, amenity grass phenolic extracts (AGPE) offer appreciable amounts of unbound/free ferulic acid that would be available for rapid in vivo absorption. The literature has shown ferulic acid to be a highly available and health benefitting phenolic compound. Chapter 1 in vitro studies demonstrated AGPE-induced antiproliferation and apoptotic induction capacities in HepG2 and Caco-2 carcinoma cell lines. The in vitro chemopreventive influences were shown to be dependent upon AGPE species, extract fraction, dose, and cell line. As with most natural systems, a significant gap in knowledge exists as to how such health promoting components modulate metabolism to maintain health. Thus, the objective of Chapter 2 was to monitor the metabolic alterations attributed to supina bluegrass and bermudagrass phenolic treatments in human hepatocellular liver carcinoma cells, HepG2, using Fourier Transform mid infrared (FT-mIR) spectroscopy. The FT-mIR metabolomic method was used to assess temporal changes in the biochemical fingerprint of treated and untreated HepG2 cells compared to resveratrol positive control treatments. The results from this study illustrate amenity grass nutraceutical targets within the HepG2 metabolme compared to the documented biochemical influences of resveratrol. As an outcome to this study, the impacts of nutraceutical stimuli on the biochemical fingerprint were further elucidated by analyzing the ability of phenolics to downregulate the oxidative nature of cancer.
Adviser: Roch Gaussoin
2011-04-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/23
https://digitalcommons.unl.edu/context/agronhortdiss/article/1026/viewcontent/Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Horticulture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1027
2011-04-18T15:10:33Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Impact of Student Motivation in Online Learning Activities
Lathrop, Amy
With the prevalence of online learning in education for both distance and campus-based students, it is critical to determine how to design electronic learning materials that tailor to student motivation and facilitate learning. Students were asked to complete an online plant breeding activity, motivation survey and an online learning quiz related to the activity. The control group of students was those who elected not to complete the activity, while the experimental group of students chose to complete the activity. Motivation scores were compared between control and experiment groups, courses, and gender using independent sample t-tests. Pearson correlations were also used to determine if correlations existed between various motivational aspects, motivation aspects and quiz scores, or overall motivation and quiz scores. Data analysis revealed correlations between motivation and quiz score; self-efficacy and quiz score, and active learning strategies and quiz score. Furthermore performance goal motivation does not differ between motivation levels. Only a difference in learning environment stimulation between males and females was uncovered. Using these findings instructors can better design online learning objects and alter the online learning environment to improve student performance in science education.
Advisers: Deana Namuth-Covert and Donald Lee
2011-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/24
https://digitalcommons.unl.edu/context/agronhortdiss/article/1027/viewcontent/Amy_Lathrop_Thesis_for_Printing_and_Digital_Commons.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
science education
student motivation
plant breeding education
Plant Breeding and Genetics
Plant Sciences
Science and Mathematics Education
oai:digitalcommons.unl.edu:agronhortdiss-1028
2011-07-01T14:58:47Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Biology, Systematics, Phylogenetic Analysis and DNA Character-Based Species Diagnosis of the False Root-Knot Nematode <i>Nacobbus aberrans</i> (Thorne, 1935) Thorne & Allen 1944 (Nemata:Pratylenchidae)
Ramirez-Suarez, Angel
The False Root-Knot nematode Nacobbus aberrans is a plant parasitic nematode that causes yield losses in several crops and plant protection agencies have established regulations to prevent infestations from spreading to new agricultural areas. The taxonomic status of the nematode has been the subject of controversy due to wide degree of variation exhibited by the species. This variability has led to the suggestion that N. aberrans is actually a species complex rather than a single species. In order to test this hypothesis, we compared twelve N. aberrans populations, which include isolates from western Nebraska, two distinct regions of Mexico and the lowlands of Argentina. The specimens were obtained from different hosts and analyzed by physiological, morphological, phylogenetic approaches. The physiological response of the nematode cultured on a common host together with the variation detected in the multivariate morphometric analysis revealed a slight tendency to differentiate groups. This intraspecific variation was confirmed and clarified using phylogenetic inference of nuclear and mitochondrial markers. Analysis of these molecular markers resolved four groups that displayed a well-defined geographic pattern of distribution. The following discrete groupings were recognized: I. Nebraska, II. Mexican North region, III. Mexican Central region, IV. The Argentinean lowlands. The median-joining network analysis of mitochondrial marker was congruent with the four geographic and genetic lineages and separated from each other by a genetic distance of 63-92 mutational steps. AMOVA analysis of the four groups revealed significant differences among the hierarchical levels, with the vast majority of the genetic variation concentrated among the four geographic groups. A character-based barcode analysis allowed identification of “pure” diagnostic characters for each group that contributed further evidence that N. aberrans is a species complex composed of at least four species. The population from Nebraska meets the criteria for consideration as a separate species. We recommend that this isolate be reinstated to N. batatiformis Thorne and Schuster, 1956 as it was originally described.
Advisor: Thomas O. Powers
2011-06-27T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/25
https://digitalcommons.unl.edu/context/agronhortdiss/article/1028/viewcontent/Dissertation_Ramirez_Suarez_Angel.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Nacobbus
False Root-knot nematode
Systematics
DNA barcoding
Nucleotide character-based diagnosis
Agronomy and Crop Sciences
Evolution
Horticulture
Plant Pathology
Plant Sciences
Population Biology
oai:digitalcommons.unl.edu:agronhortdiss-1029
2011-07-12T18:48:48Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Remarkable Features of the Hotdog-fold Thioesterases Involved in Phylloquinone (vitamin K1) Biosynthesis
Widhalm, Joshua R
Phylloquinone (vitamin K1) is a bipartite molecule, consisting of a naphthoquinone ring attached to a phytyl side chain, that is synthesized by plants and certain cyanobacteria to serve as an electron carrier in photosystem I. The coupling of the ring and isoprenyl moieties relies on the cleavage of the CoA-thioester linkage with 1,4-dihydroxy-2- naphthoate (DHNA). It has long been a mystery if this hydrolysis is an enzymatic or chemical process. Using comparative genomics, protein biochemistry, genetics and metabolic profiling, we identified a cyanobacterial thioesterase responsible for the in vivo hydrolysis of DHNA-CoA. This enzyme bears a signature domain of the 4- hydroxybenzoyl-CoA thioesterase (4HBT) family of Hotdog-fold proteins.
Surprisingly, plants, which obtained most of their phylloquinone biosynthetic genes with the acquisition of the plastid, do not contain orthologs of cyanobacterial DHNA-CoA thioesterase. We tested all of the predicted 4HBT Hotdog-fold proteins in Arabidopsis by functional complementation of the cyanobacterial mutant. We found two genes encoding functional DHNA-CoA thioesterases that display low percentages of identity and dissimilar catalytic motifs from their cyanobacterial counterparts. It appears that plant DHNA-CoA thioesterases originated from a horizontal gene transfer with a species of the Lactobacillales order. The cognate T-DNA knockout lines exhibit reduced DHNA-CoA thioesterase activity and phylloquinone content. Fluorescently tagging the Arabidopsis enzymes revealed that they are localized to the peroxisome. Subcellular fractionation assays confirmed this providing the first biochemical evidence for the involvement of peroxisomes in phylloquinone biosynthesis.
Recent proteomics and GFP-reporter projects suggest that the two steps preceding DHNA-CoA thioesterase are also peroxisomal. Thus, the current model of phylloquinone biosynthesis reflects a split between plastids and peroxisomes, implying the movement of intermediates between the organelles. To assess the importance of the cognate transport steps, we have re-routed the peroxisomal branch of the pathway to plastids in Camelina sativa. Here we report the findings of our metabolic engineering strategy on the pool of phylloquinone.
2011-07-12T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/26
https://digitalcommons.unl.edu/context/agronhortdiss/article/1029/viewcontent/Widhalm_Joshua_Dissertation.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Biochemistry
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1030
2011-07-26T16:55:14Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Hydrologic Effectiveness and Plant Survivability in the Holmes Lake Rain Garden Pilot Program: Year Three
Liebsch, Marilyn K
Rain gardens are increasingly being used as small scale stormwater best management practices (BMPs) to reduce stormwater runoff through infiltration and to remove pollutants through filtration. In 2007, as part of a comprehensive water quality restoration process of Holmes Lake in Lincoln, Nebraska, 20 pilot rain gardens were installed in residential and school properties in the watershed. Currently, assessment and monitoring has been limited to participant surveys and cannot be used to determine if hydraulic or vegetative problems exist within the garden area. In this study, visual inspections were conducted to establish a database standard for successful rain gardens, hydraulic and/or vegetative problems were noted, followed by interviews with rain garden owners. Of the 18 surveyed rain gardens, several issues appeared that were attributable to garden revisions by property owners. In all but three gardens, there was an overall problem with plant survivability. Issues more closely studied included use of sprinkler systems, hydraulic function, and plant placement within the garden. Plant placement appears to be a major concern relative to plant survivability. Plant lists need to be updated to include where a plant will do best within the rain garden depression and the installer needs to be further educated on these findings. This study also shows that visual inspections can be an efficient and low cost, effective way to detect problems within a residential rain garden.
2011-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/27
https://digitalcommons.unl.edu/context/agronhortdiss/article/1030/viewcontent/Liebsch_2011.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
stormwater runoff
BMPs
hydraulic function
groundwater recharge
impervious surface
watershed.
Horticulture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1031
2011-07-26T20:34:41Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Disease and Insect Resistance and Quality Characterization of Six CIMMYT Synthetic Hexaploid Wheats
Onweller, Kayse
The germplasm sources of common wheat (Triticum aestivum L.) are eroded by selection pressures applied by plant breeders and the disappearance of landraces. The erosion causes a loss of potentially useful resistance genes, among other agronomic and quality genes. Continuously changing pathogen races and insect biotypes affecting the Great Plains requires identification of new sources of resistance. Synthetic hexaploid wheats (SHWs), T. turgidum (BBAA) x T. tauschii (DD) hybridizations, offer ways to utilize resistances trapped in the diploid and tetraploid ancestors of common wheat. Six SHWs were assayed for resistance to a variety of fungal diseases, viruses, and aphids to determine their spectrum of resistance. The six SHWs possessed a combination of resistance to races TPMK, TTTT, and the Ug99 family; races of the causal agent stem rust (Puccinia graminis f. sp. tritici); the causal agent of stripe rust (P. striiformis f. sp. tritici) race Pst-100, and the greenbug aphid [Schizaphis graminum Rondani (Homoptera: Aphididae)] biotypes E, I and K. Additionally, the high molecular weight glutenin (HMW) alleles were studied. The HMW allele combinations were different from those commonly found in current Great Plains wheats. The allele combinations included the Glu-B alleles 14+15, 20x+20y, 6*+8*, 6+8 and 7+8. Glu-D alleles present included 2+12 and 2+T2.
Upon discovering NSGC 9711 and PI 648810 were resistant to greenbug aphid, plant populations previously developed were employed to uncover the inheritance of the resistance. A series of tests were conducted using F1s, F2s, F2:3s and BC1F2s. A single dominant gene hypothesis was rejected due to an overabundance of susceptible individuals in the F2 and F2:3 populations. However, the F2:3 and BC1F2 families indicated resistance in both synthetics was from a single dominant gene, thus NSGC 9711 and PI 648810 is reported to carry a single dominant gene for resistance to greenbug biotype E.
Adviser: P. Stephen Baenziger
2011-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/28
https://digitalcommons.unl.edu/context/agronhortdiss/article/1031/viewcontent/Kayse_Onweller_Master_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Synthetic hexaploid
disease
insect
segregation
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1032
2011-07-27T21:42:18Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
TRANSPIRATION-USE EFFICIENCY COEFFICIENT OF SEVEN WEED SPECIES AS AFFECTED BY FRACTION OF TRANSPIRABLE SOIL WATER AND GROWTH STAGE
Mannam, Venkatarao
Transpiration-use efficiency coefficient (Kc) describes the amount of biomass produced per unit transpiration at a given vapor pressure deficit. A series of greenhouse experiments were conducted to determine the Kc values of seven weed species and to measure how Kc values were affected by fraction of transpirable soil water (FTSW) level and plant growth stage. Experiments were conducted using a factorial design with 4 levels of water stress (0.3, 0.4, 0.7, and 1.0 FTSW) and two harvest times (first bloom and seed maturity). After plants attained a predetermined size, each plant was sealed at the base using a polyethylene bag. Pots were weighed daily and maintained the required weight by watering through an inserted syringe. Pre-bagging transpiration was back-calculated from 0 d to the first 20 d of measured daily transpiration. One set of plants was harvested at first bloom and another set was harvested at seed maturity. Kc was calculated as the ratio of total biomass to the cumulative transpiration multiplied by the average daytime vapor pressure deficit.
FTSW level did not affect the Kc of henbit (vegetative growth) or shepherd’s purse. Kc values increased as FTSW levels declined for common lambsquarters, pinnate tansymustard, henbit (complete lifecycle) and field pennycress (vegetative growth). Kc values decreased as FTSW declined for dandelion, Carolina foxtail, and field pennycress (complete lifecycle) suggesting that these species were relatively sensitive to water stress. Plant growth stage did not affect Kc for pinnate tansymustard and dandelion. Kc values decreased between the first bloom and seed maturity for field pennycress, common lambsquarters, shepherd’s-purse and henbit. The decline in Kc may be attributed to high oil content in the seed of field pennycress, shepherd’s-purse and henbit, and the highprotein content of common lambsquarters. Carolina foxtail Kc values did not respond consistently to FTSW across harvest times – Kc values increased from first bloom to seed maturity at FTSW levels 0.3 and 0.4, but remained same at the 0.7 FTSW level.
Advisor: Mark L. Bernards
2011-07-27T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/29
https://digitalcommons.unl.edu/context/agronhortdiss/article/1032/viewcontent/MS_Thesis_Numbered_Mannam.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Transpiration-use efficiency coefficient
winter annuals
bagging
Agriculture
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1033
2011-07-28T21:30:25Z
publication:plantpath
publication:plantpathfungal
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
GATA-Family Transcription Factors in <i>Magnaporthe oryzae</i>
Quispe, Cristian F.
The filamentous fungus, Magnaporthe oryzae, responsible for blast rice disease, destroys around 10-30% of the rice crop annually. Infection begins when the specialized infection structure, the appressorium, generates enormous internal turgor pressure through the accumulation of glycerol. This turgor acts on a penetration peg emerging at the base of the cell, causing it to breach the leaf surface allowing its infection.
The enzyme trehalose-6- phosphate synthase (Tps1) is a central regulator of the transition from appressorium development to infectious hyphal growth. In the first chapter we show that initiation of rice blast disease requires a regulatory mechanism involving an NADPH sensor protein, Tps1, a set of NADP-dependent transcriptional inhibitors and the nonconsuming interconversion of NADPH and NADP acting as signal transducer.
The Tps1-dependent Nmr inhibitor proteins regulate the activity of GATA-family transcription factors that are involved in several essential aspects of the life style of the fungus. Thus, We elucidated that the GATA transcription factor Asd4 is
essential for pathogenicity and is a positive regulator of appressorium development and sporulation, in contrast to the GATA transcription factor Pas1 that is a negative regulator of appressorium development and sporulation.
In chapter two, we set out to understand the specific role of the GATA transcription factor Asd4. We show that Asd4 controls the activation of the Tor kinase pathway, which is essential for virulence and integrates important processes such as regulation of transcription, translation, ribosome biogenesis, trafficking and regulation of Golgi, secondary metabolism, autophagy and nitrogen metabolism. This mechanism is essential to the initiation of infection-associated autophagy during plant infection and during in planta invasion.
In summary, in this study we characterized two essential regulators, Tps1 and Asd4, in M. oryzae, and we believe that understanding the regulatory mechanisms that allow the fungus to cause disease may provide new means to control the rice blast pathogen and play an important role in ensuring global food security in the future.
Adviser: Richard A. Wilson
2011-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/30
https://digitalcommons.unl.edu/context/agronhortdiss/article/1033/viewcontent/Quispe_thesis_2011__OPTIMIZED.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Tor
GATA transcription factor
Asd4
Tps1
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Bioinformatics
Genetics
Life Sciences
Microbial Physiology
Molecular Biology
Molecular Genetics
Other Cell and Developmental Biology
Pathogenic Microbiology
Plant Biology
Plant Pathology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1034
2011-07-29T14:22:59Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Herbicide-Resistant Risk Assessment: Response of Common Nebraska Weeds to Dicamba Dose
Crespo, Roberto J
Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism of action that can be used in soybean, and to provide a tool to help manage or mitigate the evolution of other herbicide-resistant weed populations. The objectives of this thesis were to assess the risk of common Nebraska weeds developing resistance to dicamba, quantify baseline dose-response to dicamba of high-risk weed species, and survey the variability in dicamba dose-response among populations of those species. Twenty-five weed scientists were asked to estimate the risk likelihood of ten weed species evolving resistance to dicamba following the commercialization of dicamba-resistant soybean. Palmer amaranth (Amaranthus palmeri), common waterhemp (Amaranthus rudis), kochia (Kochia scoparia) and horseweed (Conyza canadensis) were rated the highest risk species. Ten populations of horseweed, 73 populations of kochia, and 41 populations of common waterhemp were collected across Nebraska. Greenhouse dose-response studies using a range of dicamba doses (0 g ae ha-1 up to 35,840 g ha-1, depending on the species) were conducted on 10 horseweed populations, 10 kochia populations, and 4 common waterhemp populations that represented a range of susceptibility to dicamba in preliminary experiments. Visual injury and dry weight data were measured 28 days after treatment (DAT), data was fit to a four-parameter log-logistic equation, and the dicamba doses necessary to achieve 90% visual injury (I90) or reduction in dry weight (GR90) were calculated for each population. There was a three-fold difference in dicamba dose necessary to achieve I90 between the least and most susceptible horseweed populations, a 18.4 fold difference among kochia populations, and a 1.5 fold difference among common waterhemp populations. Similar variation in susceptibility for each species was calculated for GR90 values. Two or three replications of plants were allowed to grow for 84-228 DAT. The maximum dicamba dose (g ha-1) at which a population was able to reproduce was 280 for horseweed, 8,960 for kochia, and 560 for common waterhemp. One population of kochia was classified as “dicamba-resistant.” Individuals who adopt dicamba-resistant soybean should use multiple methods to control high-risk species to reduce the risk of dicamba-resistant weeds becoming widespread.
Adviser: Mark L. Bernards
2011-07-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/31
https://digitalcommons.unl.edu/context/agronhortdiss/article/1034/viewcontent/Roberto_Javier_Crespo___MS_Thesis_DICAMBA_FINAL_July28_2011.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
risk assessment
herbicide resistant
dicamba
dicamba-resistant soybean
kochia
horseweed
waterhemp
dose-response
marestail
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Evolution
Genetics
Plant Biology
Plant Breeding and Genetics
Plant Sciences
Population Biology
Systems Biology
oai:digitalcommons.unl.edu:agronhortdiss-1035
2019-02-26T15:53:49Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
EVALUATION OF ALGORITHM THRESHOLDS FOR CROP CANOPY SENSOR-BASED IN-SEASON NITROGEN APPLICATION IN CORN
Krienke, Brian T.
Nitrogen fertilizer is frequently the most limiting nutrient in corn production. Typically most nitrogen is applied before planting. Since nitrogen can leave the soil system fairly easily, the result can be an inefficient use of nitrogen fertilizer. Previous research has shown increased efficiency with no reduction in yield by applying nitrogen later in the season when the crop is actively growing, with rates regulated spatially through the use of active crop canopy sensors. This study evaluated the potential for N cutoff thresholds using a sufficiency index as the threshold value for areas with poor stand or an unrecoverable N deficiency. In this study the algorithm developed by Solari, et al. (2010) was used. Field scale treatments were imposed on six irrigated fields in south-central and western Nebraska to evaluate performance of the active crop canopy sensor-based in-season N management algorithm with and without predicted permanent yield loss thresholds. The study found no consistent advantage in yield, nitrogen use efficiency, or profit with sensor-based treatments using algorithm thresholds. The uniform, soil-test-based UNL treatment was most often the most profitable treatment. Further research is needed to revise the Solari, et al. (2010) method to account for soil-N supply prior to and following in-season N application.
Adviser: Richard Ferguson
2011-07-29T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/32
https://digitalcommons.unl.edu/context/agronhortdiss/article/1035/viewcontent/Thesis_12_sub_BK.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
active crop canopy sensors
algorithm thresholds
threshold
variable rate nitrogen
variable rate
corn
nitrogen
Physical Sciences and Mathematics
Plant Sciences
Soil Science
oai:digitalcommons.unl.edu:agronhortdiss-1036
2011-07-29T19:19:31Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
The Rate of Shattercane x Sorghum Hybridization <i>in situ</i>
Schmidt, Jared J
Cultivated sorghum (Sorghum bicolor subsp. bicolor) can interbreed with its close weedy relative shattercane (S. bicolor subsp. drummondii). The introduction of traits from cultivated sorghum into a shattercane population could contribute to the invasiveness of the wild shattercane population. An in situ experiment was conducted across two years to determine the potential for pollen-mediated gene flow from grain sorghum to shattercane. Shattercane with juicy midrib (dd) was planted in a soybean field in concentric arcs at varying distances from a sorghum pollen source with dry midrib (DD). The arcs were placed so that prevailing winds would carry pollen from the sorghum to shattercane. Shattercane panicles in anthesis during sorghum pollen shed were tagged and seeds were collected from those shattercane panicles. Progeny were evaluated using the dry midrib marker to determine outcrossing rate. Outcrossing was greatest for shattercane placed within the source and differed between years (3.6±0.76% in 2008 and 16.1±1.31% in 2009). Outcrossing rate generally declined as distance increased for both years. In both years outcrossing was seen (0.09±0.04% in 2008 and 0.34 ±0.07% in 2009) at the farthest distance evaluated (200 m). Wind direction and speed was also a determining factor as wind run (wind speed*proportion of wind in that direction) affected outcrossing rate for all pollination periods. Results indicate that genes from cultivated sorghum and any associated traits will likely be introduced into shattercane populations at distances of at least 200 m and that outcrossing rate is dependent on weather factors such as wind, and possibly pollen source strength.
Adviser: John J. Lindquist
2011-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/33
https://digitalcommons.unl.edu/context/agronhortdiss/article/1036/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Sorghum
shattercane
gene flow
transgenic
herbicide resistance
Agriculture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1037
2011-07-29T19:37:24Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Twin-Row Production and Optimal Plant Population for Modern Maize Hybrids
Novacek, Mitchell J.
Maize (Zea mays L.) is widely grown for food, feed, and fuel, and optimal yield will be required to meet increasing demand due to world population growth and increased biofuel usage. This requires matching of the best maize hybrids with optimal plant population and spacing. Modern maize hybrids have increased “crowding stress” tolerance, and Bt (Bacillus thuringiensis) hybrids now resist European corn borer and corn rootworm which has created interest in altering row configuration and increasing plant population.
Three Bt hybrids were evaluated from 2009 to 2010 near Mead, NE at target populations from 69136 to 106173 plants ha-1 in 76 cm single rows and twin rows. Maximum yield occurred at the highest target population in 9 of 12 year, hybrid, and row configuration combinations although target population had a small effect on yield. Varying hybrid, plant population, and row configuration had small and inconsistent effects on grain yield, yield components, plant morphology and leaf area, interception of solar radiation, and stalk lodging. It appears that the major impacts of altering row configuration occur early in the growing season, and plant growth and other factors occurring later in the growing season have a greater impact on yield.
Two pairs of near isogenic Bt and non-Bt maize hybrids were evaluated under rainfed and irrigated conditions from 2008 to 2010 at target populations from 49383 to 111111 plants ha-1 near Mead, NE. For all hybrids and environments, yield increased linearly and the highest target population resulted in the greatest grain yield. Bt hybrids had 0.4 Mg ha-1 greater yield than non-Bt hybrids at all populations. Bt hybrids lodged less in three of five environments.
Results indicate that twin-row production has little influence on maize yield and growth in Nebraska. In general, maize yield increased linearly with increasing target population although the rate of yield increase varied across experiments, environments and hybrids. Farmers in East-Central Nebraska should consider increasing maize plant population and planting Bt hybrids to optimize maize grain yield.
2011-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/34
https://digitalcommons.unl.edu/context/agronhortdiss/article/1037/viewcontent/Novacek_Thesis_7_29_11_Draft.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
twin-row production
row configuration
plant population
plant density
maize hybrid
stalk lodging
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1038
2011-10-31T16:57:11Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
GENETICS OF POLYPHENOL OXIDASE (PPO) ACTIVITY IN WHEAT (<i>TRITICUM AESTIVUM</i> L.)
Onto, Somrudee
The enzyme activity of polyphenol oxidase (PPO) in grain is regarded as a major factor in time-dependent darkening and discoloration of wheat food products during processing or storage. The darkening phenomena of products reduce the quality of products and affect consumer acceptance. Breeding wheat cultivars with low PPO activity is the best way to reduce the undesirable darkening. The low PPO line PI 117635 was crossed to two low PPO wheats from Idaho, IDO580 and IDO377s to determine whether matings between wheats with low levels of grain PPO would result in complementation, and lines with lower or nil PPO would be generated. The F3:4 population derived from PI 117635/IDO580 showed no variation in PPO activity. The F3:5 and F3:6 populations derived from PI 117635/IDO377s grown at Yuma and Oregon fields in 2009 were analyzed for PPO activity and used to determine whether lines with nil PPO activity were generated. Of the 239 lines, 154 lines were identified to have PPO activity that was not significantly different from Ben durum wheat using t-test. STS markers, PPO18, PPO29, and STS01 were used to test lines possibly with either low or high PPO levels at Ppo-A1 and Ppo-D1 loci. All lines were fixed for the low PPO allele at Ppo-A1. However, PPO29 and STS01 showed the opposite results from the Ppo-D1 allele prediction. To examine inheritance of PPO activity in multiple wheat genetic backgrounds and to evaluate the relationship between PPO activity and alleles at two PPO loci, 5 populations (PI 117635/Antelope; Fielder/NE03681; Fielder/Antelope; NW07OR1070/Antelope; NW07OR1066/OR2050272H) were developed. STS markers were used to identify the genotypes and a putative third (null) genotype at Ppo-A1 allele was discovered in NW07OR1066 and NW07OR1070 lines. ANOVA showed all populations had significant genotypic effects on PPO activity. The generations and genotype nested within generation effects were not significant in all populations. The NW07OR1070/Antelope and NW07OR1066/OR2050272H populations had the lowest PPO activities because both populations had a null allele for Ppo-A1 on chromosome 2A. Of all 5 populations, 3 populations found the reverse results of Ppo-D1 allele from the previously reported research, indicating the markers for Ppo-D1 allele give erroneous results in some genetic backgrounds.
Advisor: P. Stephen Baenziger
2011-10-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/35
https://digitalcommons.unl.edu/context/agronhortdiss/article/1038/viewcontent/Onto__Somrudee_dissertation_2011__embedded.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1039
2011-11-28T23:08:32Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
INTEGRATION OF PLANT-BASED CANOPY SENSORS FOR SITE-SPECIFIC NITROGEN MANAGEMENT
Shiratsuchi, Luciano S.
The soil’s nitrogen (N) supply can vary drastically in the field, spatially as well as temporally making any soil prediction difficult even with very detailed mapping. Consequently, a plant-based approach wherein the measured canopy can indicate the N needs in a reactive and spatially-variable way can be a better approach than mapping, because integrate the soil N supply and translate the crop need on-the-go. The first experiment evaluated the performance of various spectral indices for sensing N status of corn, where spectral variability might be confounded by water-induced variations in crop reflectance. We found that water and previous crops effects on vegetation indices (VI) must be considered, and also that some VIs are less susceptible to water with good ability for N differentiation. In the second experiment, the objective was to develop an approach that relies on local soil conditions as well as on active canopy sensor measurements for real-time adjustment of N application rate. We found that local variations in plant N availability must be considered to determine the optimal N rate on-the-go, and that the localized reference incorporated the spatial variability of the N-rich plot. Next, we determined the correlation between active canopy sensors assessments of N availability and ultrasonic sensor measurements of canopy height at several growth stages for corn. We found strong correlations between both sensors and that they had similar abilities to distinguish N-mediated differences in canopy development. The integrated use of both sensors improved the N estimation compared to the isolated use of either sensor. Based on these strong correlations, we developed an N recommendation algorithm based on ultrasonic plant height measurements to be used for on-the-go variable rate N application. Lastly, we evaluated the crop water status using infrared thermometry integrated with optical and ultrasonic sensors, we concluded that the integration of sensors was beneficial to detect water-stressed zones in the field, affecting yield and possibly promising to delineate zones for N and water management.
Advisors: Richard B. Ferguson and John F. Shanahan
2011-11-18T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/36
https://digitalcommons.unl.edu/context/agronhortdiss/article/1039/viewcontent/PhD_Dissertation_Final.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
precision agriculture
active canopy sensors
canopy temperature
ultrasonic sensor
proximal remote sensing
nitrogen management
variable rate technology
Agriculture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1040
2011-11-30T20:23:46Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
The Chemical Nature and Distribution of Black Pigment in Soil
Gillam, William Sherman
As used in this paper, humus refers to that portion of the soil organic matter peptized by four per cent ammonium hydroxide. That fraction peptized by four per cent ammonium hydroxide, precipitated by acids, and insoluble in alcohol, is designated as black pigment. It is called humic soil by many writers.
1938-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/37
https://digitalcommons.unl.edu/context/agronhortdiss/article/1040/viewcontent/Gillam__The_Chemical_Nature_and_Distribution_of_Black_Pigment_in_Soil__1938.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1041
2011-12-01T14:30:55Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
COMPARING CROPPING SYSTEM PRODUCTIVITY BETWEEN FIXED ROTATIONS AND A FLEXIBLE FALLOW SYSTEM USING MODELING AND HISTORICAL WEATHER DATA IN THE SEMI-ARID CENTRAL GREAT PLAINS
Miceli-Garcia, Juan Jose
In the Central Great Plains, the predominant crop rotation is winter wheat (Triticum aestivum L.)-fallow. Producers are looking to add diversity and intensity to their cropping systems by adding summer crops, however, the elimination of summer fallow may increase crop production risk. The objective of this study was to use crop simulation modeling to compare the productivity of two fixed rotations [winter wheat-corn (Zea mays L.)-fallow and winter wheat-corn-spring triticale (X Triticosecale Wittmack)] with simulated flexible fallow rotations. The flexible fallow rotations made the decision to plant triticale or use summer fallow prior to winter wheat seeding based on available soil water in spring. Data from three years of field studies at two sites, Sidney, NE and Akron, CO, were used to calibrate and test the model, AquaCrop, for the crop simulation. Twenty-three years of historical weather data from each of the two locations were used to simulate crop production for each rotation. Average income was improved by replacing summer fallow with triticale (from 120 to 160 US $ ha-1 for Akron and from 126 to 199 US $ ha-1 for Sidney), but income variability (standard deviation) also increased (from 73 to 84 US $ ha-1 for Akron and from 93 to 115 US $ ha-1 for Sidney). Risk-averse growers are likely to always use fallow in their crop rotations prior to planting winter wheat, while non-risk-averse growers will likely eliminate fallow and substitute triticale or a similar early-planted spring forage. Flexible fallow rotations seldom improved profits compared to always using fallow without also increasing income variability. The exception was Sidney using the 400 mm soil water threshold, which lowered income variability compared to always fallowing (from 93 to 91 US $ ha-1) and increased average income (from 126 to 142 US $ ha-1). However, the economic benefits of flexible fallow compared to the two fixed cropping systems were minimal.
Advisers: Drew J. Lyon and Timothy J. Arkebauer.
2010-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/38
https://digitalcommons.unl.edu/context/agronhortdiss/article/1041/viewcontent/Miceli_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Modeling
AquaCrop
wheat
corn
triticale
flexible
fallow
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1042
2011-12-05T14:33:02Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Identification of Soybean Seed Oil QTLs with Little or No Impact on Seed Protein
Sun, Yu-Kai
A QTL (Quantitative Trait Locus) is chromosomal location of a gene controlling a specific phenotypic characteristic (trait). This trait might be governed by two or more genes and may be affected by environmental interaction. The USA soybean seed composition, when averaged over years and states, is 18.7% oil and 35.3% protein. Soybean seed provides cooking oil for humans and protein for livestock. Concurrent genetic improvement of seed protein (pro) and oil content has been difficult to achieve due to the negative genetic correlation of the two traits. This negative correlation could be due to a pair of tightly linked protein and oil QTLs, whose individual alleles are linkage-paired to give rise to high pro - low oil or low pro – high oil, phenotypes, OR it could be due to just one pleiotropic QTL, whose two alleles have inverse effects on both oil and protein. This thesis objective is to find oil QTLs with minimal effect on protein. Three F2 populations were developed by mating of two high oil lines with each other and with Williams 82, a current high-yield cultivar. About 500 individual F2 plants in each population produced F2.3 seed progenies and then F2.4 seed progenies that were phenotyped for seed protein and oil content. Selective genotyping was used to genotype F2 plant progenitors of only the highest and the lowest seed oil deciles of F2.4 seed progenies. A 1536 SNP locus assay chip was used for genotyping. In the three mapping populations, eight seed oil QTLs with LOD scores greater than 3.0 were detected and mapped on seven linkage groups using R/qtl software. Six statistically significant seed oil QTLs on LG-C2 (Chr6), LG-M (Chr7), LG-B1 (Chr11), LG-F (Chr13), LG-E (Chr15), and LG-L (Chr19) were detected using genome-wide permutation tests (α = 0.05). Of the seed oil QTLs detected in this study, only the seed oil QTLs on LG-F (Chr13) have no significant impact on seed protein content. For improving the seed oil content in high yielding soybean cultivars, S17276 allele (Chr13) from the parental line RMLPC1-311-128-128 may be useful to soybean breeders to improve soybean seed oil content without effecting on seed protein content.
Advisor: James E. Specht
2011-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/39
https://digitalcommons.unl.edu/context/agronhortdiss/article/1042/viewcontent/Master_Thesis_YuKai_Sun_v2.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Soybean
seed Oil
seed Protein
QTLs
selective genotyping
SNP
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1043
2011-12-05T15:30:48Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Management Zone Delineation Techniques on Irrigated Corn in Nebraska
Bereuter, Aaron M.
Increased interest in site-specific management of irrigated corn in Nebraska has identified the need for a decision-making framework for zone delineation. Zones based on static soil and landscape properties provide a valuable foundation for variable rate management strategies. The purpose of this project was to identify the optimal soil and landscape attributes for generating management zones (MZ) of relative productivity potential. Three producer-managed cornfields across Nebraska with varying soil types, topographic characteristics, and climate regimes were identified as research sites during the 2010 growing season. Nine soil and landscape attributes were identified as potential properties for estimation of productivity potential. The attributes were broken into three groups; soil properties, spectral wavebands, and landscape attributes. Correlations between independent attributes and grain yields were used for determining the optimal soil and landscape attributes for MZ delineation. Optimum attributes were imported into Management Zone Analyst software package (MZA) for zone delineation. Correlations at each research site determined different combinations of soil and landscape attributes as the most appropriate for delineation of MZs. The attributes used in this project were assumed to be static properties. Those properties are only part of determining productivity; in-season influences also affect productivity. Evaluation of using a single MZ delineation opertation for multiple fields proved to be unproductive. MZs in different fields that are determined to have equivalent soil and landscape properties in MZA do not represent equivalent productivity potential. Although sampling density of soil and landscape attributes will determine spatial resolution of management zones, the smaller the spatial resolution the greater the precision and accuracy of the management zones as it relates to production potential. Small-scale variability will potentially be overlooked when spatial resolution of management zones is increased. Results from this project provide farmers a foundation for sit-specific management of irrigated corn in Nebraska. Adaptability of in-season management is critical to account for climatic irregularity during the growing season.
Adviser: Richard B. Ferguson
2011-12-02T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/40
https://digitalcommons.unl.edu/context/agronhortdiss/article/1043/viewcontent/Final_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Management Zones
Soil Organic Matter
Soil Electrical Conductivity
Topography
Productivity Potential
Agriculture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1044
2014-10-30T19:37:32Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Atrazine Runoff in the Blue River Basin: Geomorphology, Rainfall, and Agronomic Practices
Dhakal, Kundan
Atrazine concentrations in the Big Blue River Basin (BRB) in Nebraska and Kansas periodically exceed the U.S. EPA Maximum Contaminant Level (MCL) of 3 µg L-1. The present study is focused on watershed variables influencing surface runoff of atrazine. The assessment includes the impact of corn and sorghum planting progress (indicating atrazine application), rainfall, antecedent soil water content, and soil restrictive layer on stream-measured weekly atrazine load in independent BRB subwatersheds for 1997 - 2004. Maximum atrazine loading occurred after most of the corn had been planted but during sorghum planting from mid-May to early June, immediately following multiple rainfall events that saturated the soil profile and caused runoff from fields. Analysis of covariance was conducted from day 110 when about 10% of the corn was planted to day 170 when 90% of the sorghum was planted. Results from the independent subwatersheds imply that atrazine load weighted by area is related to cumulative weekly rainfall across all years. Statistical analysis showed rainfall was the most significant factor associated with atrazine loading, but soil water content, corn and sorghum planting progress, and the presence of a restrictive layer at the soil surface were also important.
Adviser: Patrick J. Shea.
2004-12-02T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/41
https://digitalcommons.unl.edu/context/agronhortdiss/article/1044/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Atrazine
Surface runoff
Subwatershed
Agriculture
Agronomy and Crop Sciences
Environmental Health
Environmental Indicators and Impact Assessment
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1045
2011-12-12T14:48:39Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
The Effect of Residue C:N Ratio on the Turnover of N and C in Various Soil Organic Matter Fractions
Wingeyer, Ana B
Identifying soil organic matter (SOM) fractions that contribute to soil indigenous nitrogen (N) supply and understanding their turnover under different management constitute necessary tools toward an efficient N use. The objectives of this study were: i) trace the endpoint of carbon (C) flux from residue inputs into SOM; and ii) asses the role of the light fraction (LF), mobile humic acid (MHA) fraction and calcium humate (CaHA) fraction as N sources for heterotrophic decomposition of fresh plant residues with contrasting C:N ratio. A long-term aerobic soil incubation was carried out on 15N-labeled soil samples from Lincoln and Mead, NE. Pre-incubation three residue treatments were assigned: MAIZE stover; SOYBEAN leaves, and NO-RESIDUE added. Pre- and post-incubation LF, MHA and CaHA were extracted. The soil was periodically leached, and the leachate was analyzed for N and 15N atom%. SOM fractions were analyzed for %C, %N, δ13C‰ and 15Natom%. Cumulative mineralized N was ~60% higher at Mead. MAIZE addition resulted in N immobilization at Mead (until t=90d) and Lincoln (until t=300d), while SOYBEAN increased N mineralization by 42% at Lincoln and 23% at Mead. Post-incubation, CaHA mass was reduced by 16 and 11% at Lincoln and Mead, respectively, and MHA and LF mass varied among treatments , with a significant increase of both fractions at Lincoln and no differences at Mead. All SOM fractions had a significant loss of 15Natom% and 15N mass across treatments. The relationship between 15N mass loss and change in N mass indicated CaHA as a N donor fraction with a preferentiall loss of recently added materials. The turnover of MHA reflected a wider range of situations. A N donor under N mineralization at Mead, and N and C storage under N immobilization at Lincoln. The LF %C4-C increased under MAIZE, supporting LF as the primary pool for residues into SOM. This study indicates that the C and N flux from Residue > LF > MHA > CaHA, can be modified to CaHA > MB > MHA > LF under high N demand for decomposition of C, where both humic fractions constitute N sources to LF and residue decomposition.
2007-09-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/42
https://digitalcommons.unl.edu/context/agronhortdiss/article/1045/viewcontent/Thesis_Ana_Wingeyer.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Humic acids
light fraction
15N
13C
ecological intensification
N mineralization
indigenous soil N supply
soil incubation
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Biochemistry
Environmental Microbiology and Microbial Ecology
Life Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1046
2012-03-21T17:22:24Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Impact of Crop and Residue Management on the Physical and Chemical Stabilization of Soil Organic Matter at Farm Level
Wingeyer, Ana B
This dissertation explores changes over time in soil organic matter (SOM) stabilization of two irrigated production fields: a continuous maize sequence that was converted from no-till to conservation deep tillage (Site 1), and a no-till maize-soybean rotation (Site 2). An integrated approach using humic acid extractions and density-based physical fractionation of SOM within aggregate size classes was developed to evaluate the changes in SOM stabilization (physical protection, organo-mineral associations and humification). At Site 1, loss of SOM in the surface layer was compensated for by increased SOM in deeper soil layers with no net change in C stocks. Whole field C-stocks in the 0-400 kg soil m-2 layer of Site 1 were 7.09 ± 0.29, 7.47 ± 0.36, 7.15 ± 0.37 and 7.18 ± 0.41 kg C m-2 in fall of 2005, 2006, 2007 and 2008, respectively. This outcome is encouraging, given the challenge of stabilizing aboveground residues into the mineral matrix without increasing tillage-induced C losses from native SOM and residues due to enhanced decomposition. At Site 2, there was an increase in C and N stocks in surface soil after the second maize year (2007). Whole field C stocks in the 0-400 kg soil m-2 layer of Site 2 were 6.42 ± 0.30, 6.18 ± 0.32, 6.81 ± 0.26 and 6.72 ± 0.29 kg C m-2 in fall of 2005, 2006, 2007 and 2008, respectively. The changes in soil 13C signature and monosaccharide composition, together with changes in SOM fraction amount support a large input of soybean residues as key to promote stabilization of standing maize litter through physical protection and humification. Preferential SOM accumulation in the largest, most C-enriched aggregates was associated with less humified SOM fractions while similar accumulation rates of more humified fractions were found among aggregate classes. These findings support stabilization of crop residues as SOM under high yield maize and soybean management at field scale.
Advisers: Rhae Drijber and Daniel Olk
2011-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/43
https://digitalcommons.unl.edu/context/agronhortdiss/article/1046/viewcontent/AnaWingeyer_PhD_2011_Revised.pdf
https://digitalcommons.unl.edu/context/agronhortdiss/article/1046/filename/0/type/additional/viewcontent/data1.xls
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Humification
organo-mineral associations
physical protection
nitrogen availability
fall conservation deep tillage
no-till
continuous maize
maize-soybean rotation
residue quality
Agriculture
Biochemistry
Microbiology
Other Life Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1047
2012-01-19T14:37:04Z
publication:bioscipapers
publication:biosciecology
publication:biologicalsciences
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Researches in the Genus <i>Taraxacum</i>
Sears, Paul B.
These researches were undertaken with a view to working out certain little known phases of the life history of our local species of dandelion, and particularly with a view to confirming or disproving the following widely accepted conjecture of Raunkjiaer;
"Species Danicae Taraxaci castratione agamice propagari demonstratum est; species onmes Taraxaci semper parthenogenetice propagari verisimile est."
The problem has been found to involve difficulties and obscurities which will require considerable time to effectually disentangle, but results have already been secured which we believe ourselves justified in setting forth.
During the work we have been much in debt to the late Dr. Charles E. Bessey for his cheerfully given and suggestive help, as well as to his associates and to Dr. Florence McCormick for kindly aid.
1915-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/44
https://digitalcommons.unl.edu/context/agronhortdiss/article/1047/viewcontent/Sears_MA_thesis_1915.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
dandelion
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1049
2012-03-02T18:29:06Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
The Hormonal Characterization and Mapping of a New Jasmonate Hypersensitive Mutant (<i>jah2</i>) in <i>Arabidopsis thaliana</i>
Wei, Hsin-Ho
Jasmonic acid (JA) is a phytohormone that plays important roles in growth, development, and defense in plants. Although many functions and mechanisms of JA are known, some pathways are still unclear. One of the simplest approaches to understanding JA signal transduction is isolating mutants that respond abnormally to JA. From the defects of such mutants we can determine the regulatory functions of JA. jasmonate hypersensitive 2 (jah2) is a JA hypersensitive mutant. JA normally inhibits the root growth of plants and the jah2 mutant has an even shorter root compared with wild-type Col-0 (wild type) under the same JA concentration. Examination of the sensitivity of jah2 showed that jah2 and WT have a 100-fold JA-sensitivity difference. While jah2 was hypersensitive to JA, it was not hypersensitive to two other hormones, IAA and the precursor of ethylene, ACC. Two types of PCR-based markers (CAPS and SSLP) were used to map jah2. The jah2 mutant (in Col-0) was crossed with Ler to generate recombinants with sequence polymorphisms between the two ecotypes. F2 mutants homozygous for the jah2 phenotype were selected from JA-containing agar media. Initially, bulk segregant analysis was used until a linked marker was found; afterwards individual F2 mutants were tested. The jah2 area was narrowed down to a region of about 177kb on Chromosome 5. Illumina whole genome sequence analysis of jah2 was compared with a reference wild type sequence. The jah2 mutant had two G-A single nucleotide transitions within the mapped area. One was in an intergenic region and the other was in intron six of glutathione synthetase gene (GSH2). This suggests that GSH2 is the mutated gene in jah2, which is consistent with previous findings that JA signaling has some interactions with glutathione and redox signaling in plants.
2012-02-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/46
https://digitalcommons.unl.edu/context/agronhortdiss/article/1049/viewcontent/Hsin_Ho_Wei_s_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
jasmonic acid
Arabidopsis mutant
jah2
molecular marker
CAPS
SSLP
mapping
glutathione synthetase 2 (GSH2)
Agronomy and Crop Sciences
Plant Biology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1050
2018-04-18T18:23:43Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Diversification of Organic Cropping Systems with Cover Crop Mixtures: Influence on Weed Communities, Soil Microbial Community Structure, Soil Moisture and Nitrogen, and Crop Yield
Wortman, Samuel E.
Organic grain cropping systems typically depend on intensive mechanical cultivation for weed control and manure or compost applications to meet plant nutrient demands. However, cover crops may contribute to weed suppression and soil fertility, potentially increasing crop yield and sustainability of the system. The utility of individual cover crop species have been well documented, but the agronomic benefits of diverse cover crop mixtures have received less attention. Cover crop mixtures are an appealing option for farmers, as increasing species diversity has been shown to increase resource-use efficiency, stability, resiliency, and productivity of plant communities. Despite the growing interest in cover crop mixtures, little is known about the effect of increasing cover crop diversity on cropping system performance. Moreover, organic farmers have questions about the most effective method for cover crop mixture termination.
In an effort to increase knowledge about cover crop mixtures and management for the western Corn Belt, an organic cropping systems trial was initiated in 2009 at the UNL ARDC near Mead, NE. Spring-sown mixtures of cover crops, ranging from two to eight species, were included in a sunflower – soybean – corn crop rotation. Cover crops were planted in late-March and terminated mechanically with either a field disk or sweep plow undercutter in late-May. Changes in cover crop mixture influenced cover crop productivity and early-season weed biomass, while termination method drove differences in weed community composition, soil microbial community structure, soil moisture and nitrogen, and crop yield. Interestingly, the management of ambient weed communities as a cover crop led to unique shifts in soil microbial community structure, but did not alter soil nitrogen or crop yield when compared to cover crop mixtures. When considering cropping system performance in combination with potential environmental benefits, diverse cover crop mixtures paired with a sweep plow undercutter for termination seems to be a profitable and sustainable management option for organic grain farmers in the western Corn Belt.
2012-04-06T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/47
https://digitalcommons.unl.edu/context/agronhortdiss/article/1050/viewcontent/Sam_Wortman_PhD_Dissertation__Final_Version_.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agriculture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1051
2012-04-19T15:15:56Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Comparison of Methods and Corn Root Types for Efficient Extraction of Endoparasitic Nematodes
Behn, Jae L.
Endoparasitic nematodes annually reduced the yield of corn in the United States. Pratylenchus spp. and Hoplolaimus spp. are endoparasitic nematode genera that parasitize corn in the Midwest. Previous research has shown nematode population densities to be highly variable and extraction methods may not provide consistent results. In order to determine more consistent and time efficient results, comparisons were made between four standard nematode extraction techniques for preferences of nematode genera for extraction method, corn root type, and extraction time. The extraction methods evaluated were aeration-incubation, a modified Baermann funnel, Seinhorst’s mister, and shaker incubation. Research plots were established at two Nebraska locations in 2009 and 2010 with documented histories of high population densities of these endoparasitic nematode genera. Nematodes were extracted from six root types on four extraction methods for 3, 5 and 7 days in a complete factorial treatment design. In 2009, Pratylenchus spp. were best extracted from the first set of anchor roots on the Baermann funnel (p < 0.0001) or in the aerated incubation. Hoplolaimus spp. had the greatest recovery from seminal roots on the Baermann funnel in 2009 (p < 0.0001). The mist extraction method did not have consistent results in 2009. For 2010, fine feeder roots in mist or aerated incubation had the greatest recovery of both genera of endoparasitic nematodes (p < 0.0001). In most comparisons, 3-5 days of incubation was sufficient to extract at least 50% of the 7 day population density. For most root types, extraction timings, and nematode genera, the shaker method yielded the fewest nematodes per gram dried root (p < 0.0001). Based on these results, it can be concluded that nematode extraction efficiency varies by genus for root type and extraction method.
Advisor: Tamra A. Jackson
2012-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/48
https://digitalcommons.unl.edu/context/agronhortdiss/article/1051/viewcontent/J._Behn_Thesis_3_20_12.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Pratylenchus
Hoplolaimus
Baermann funnel
Seinhorst mistifier
aeration incubation
shaker incubation
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1052
2012-04-23T20:51:40Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Stocking Density Affects Trampling and Use of Vegetation on Nebraska Sandhills Meadow
Johnson, Jordan R
Ultrahigh stocking density (113,000 kg·ha-1 to as high as 1 million kg·ha-1 of beef) or mob grazing has been suggested to build soil, increase forage production and plant diversity, and improve grazing distribution compared to less intensive grazing systems. Experimental evidence does not completely support such conclusions. The overall focus of this research is based on the approach of building soil by optimizing above ground plant growth coming in contact with soil surface by trampling 60% of above ground plant growth. The objective of the study was to compare the effect of mob grazing and simple rotational grazing systems on forage utilization, harvest efficiency, percentage of plant mass trampled, and animal performance of grazing cattle on a subirrigated meadow in the Nebraska Sandhills. The three different grazing methods compared in this study were: ultrahigh stocking density with a single grazing period (mob grazing); 4-pasture rotation with a single grazing period (4-PR-1); and 4-pasture rotation with two grazing period (4-PR-2). Cattle were rotated through 120 mob-grazed pastures and 4 pastures in each of the 4-pasture rotation treatments in 2010 and 2011. In 2010, the stocking density for mob grazing, 4-PR-1, and 4-PR-2 treatments was 224,170 kg·ha-1, 7,472 kg·ha-1 and 4, 982 kg·ha-1, respectively, and 201,753 kg·ha-1, 6,725 kg·ha-1 and 4, 982 kg·ha-1, respectively, in 2011. The stocking rates were uniform for the grazing treatments at 8.15 AUM·ha-1 in 2010 and 7.41 AUM·ha-1 in 2011. Grazing period per pasture for the mob grazing, 4-PR-1, 4-PR-2 grazing treatments was 0.5, 15, and 20 days, respectively. In 2010, steers trampled 58%, 39%, and 17% of the available standing crop in the mob, 4-PR-1, and 4-PR-2, respectively. Percentage trampled was 62%, 29%, and 19% for mob, 4-PR-1, and 4-PR-2, respectively in 2011. High percentage of trampling in the mob grazed pasture reduced forage intake resulting in low weight gains (0.13 kg·d-1). This long-term study will determine the effect trampling on soil organic matter, physical properties, and vegetation dynamics.
Advisors: Walter H. Schacht and Jerry D. Volesky
2012-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/49
https://digitalcommons.unl.edu/context/agronhortdiss/article/1052/viewcontent/JJohnsonThesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Ultrahigh Stocking Density
Mob Grazing
Utilization
Harvest Efficiency
Grazing Systems
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1053
2012-04-24T13:50:42Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Nest and Brood Site Selection and Survival of Greater Prairie-Chickens in the Eastern Sandhills of Nebraska
Anderson, Lars
Greater prairie-chickens (Tympanuchus cupido pinnata) are a grassland bird species of conservation concern. Although greater prairie-chickens have declined over much of their range, the Nebraska Sandhills has the largest population in North America. However, the responses of nest and brood site selection and survival to vegetation characteristics are unknown. I studied prairie-chickens on private rangelands in Rock and Brown Counties from 2009-2011. I fitted 139 females with radio collars to locate nest and brood sites and to determine nest and brood survival rates. Females were trapped on leks during the breeding season and I monitored them throughout the summer using radio telemetry. At nest and brood sites, I collected vegetation structure and composition data. Plant composition was estimated by functional groups using a quadrat method and vegetation structure was measured using the Robel pole and coverboard. I identified the ecological site and plant community at each nest and brood site. I then sampled to determine the relative availability of ecological sites and plant communities in each pasture to assess preference at a macroscale level. I also collected weather data throughout the reproductive season to assess variation in nest and brood survival. Prairie-chicken females tended to choose upland ecological sites for nesting and brood-rearing. Nest sites had more vegetation cover (VOR) (mean VOR: 10.8 cm; SD=0.7) than coupled random sites (mean VOR: 4.6 cm; SD=0.4). Nest site selection is positively associated with moderate levels of VOR and residual vegetation. Daily nest survival was poorly associated with habitat measures and was marginally associated with weather and temporal effects. Brood-rearing sites tended to have higher VOR and LD (mean VOR: 6.92 cm, SD=0.62; mean LD: 0.06 cm, SD=0.1) than at coupled random locations (mean VOR: 6.45 cm, SD=0.37; mean LD: 0.05 cm, SD=0.1). Higher forb cover and greater litter depth positively impacted daily brood survival. My research gives grassland managers much-needed information for managing prairie-chicken breeding habitat in the Nebraska Sandhills.
2012-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/50
https://digitalcommons.unl.edu/context/agronhortdiss/article/1053/viewcontent/Lars_Anderson_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
greater prairie-chicken
habitat
Nebraska
nest selection
nest survival
rangeland
Sandhills
Tympanuchus cupido pinnata
brood survival
brood selection
Agriculture
Ornithology
Other Plant Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1054
2012-05-04T19:50:49Z
publication:natres
publication:ncfwru
publication:wetlandsneb
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
INTEGRATED MANAGEMENT OF COMMON REED ALONG THE PLATTE RIVER IN NEBRASKA: CONTROL, TIMING, WATER USE, AND ECONOMIC ANALYSIS
Rapp, Ryan E
There are two biotypes of common reed, which includes the native common reed (Phragmites australis subsp. americanus) and non-native (invasive) common reed (Phragmites australis subsp. australis).The non-native biotype of common reed has invaded wetland habitats in many states of the US, including Nebraska.
Three studies, disking followed by herbicide, mowing followed by herbicide, and herbicide followed by mechanical treatment were initiated in 2008 in Nebraska. The objective was to evaluate common reed control along the Platte River using an integrated management. Herbicide followed by mechanical treatment had excellent control (≥92%) with all treatments except glyphosate applied in the summer of 2008 alone or followed by a mechanical treatment 817 DAT.
Field studies were conducted the Platte River with the objective to determine the effect of herbicide selection and timing of application on common reed. Three herbicides were applied at two rates and three growth stages of common reed. In general, common reed showed more tolerance to applications during vegetative stage, with control ratings increasing with later timings. Imazapyr provided the highest levels of control (≥92%) across all three timings, while imazamox provided the lowest level of control 60%).
Measurements of gas exchange and leaf area index were collected in undisturbed stands of both native and non-native common reed stands. Stomatal conductance and leaf assimilation on average was higher in native common reed than in non-native common reed. LAI in invasive common reed was dramatically larger on average. There was 243 mm year-1 estimated difference in transpiration with non-native common reed having a higher estimation of transpiration.
An economic analysis of common reed management options reflecting water savings and net return on investment was performed. Returns ranged from $1,326 to $4,235 per hectare over three years. Treatments of disking followed by herbicide tended to have the highest initial net return. All treatments provided a net gain return after 3 years of control of common reed.
2012-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/51
https://digitalcommons.unl.edu/context/agronhortdiss/article/1054/viewcontent/RyanRappDissertationFinal.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Integrated Weed Management
Common Reed
Phragmites australis
Invasive
Herbicide
Mechanical Control
Timing
Agriculture
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1055
2012-05-10T13:39:38Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MONITORING <i>DS</i> TRANSPOSITION IN THE SOYBEAN GENOME
Singh, Manmeet
Soybean (Glycine max (L.) Merrill) is a major oilseed commodity which partitions carbon and nitrogen flux during embryogenesis towards two primary storage reserves, protein and oil, at approximately 40% and 20%, respectively in the seed. This attribute makes soybean a valuable feedstock in many food, feed and industrial applications. Over the past decade, a wealth of genomic resources has been established for soybean that will aid in elucidating the underlying biology governing the growth and development of the crop. This in turn will foster innovative breeding and genetics approaches leading to improvements in agronomics and end-use quality. Loss- and gain-of function mutants are powerful resources that complement functional genomics programs. Here we report on the creation of a repository of transgenic soybean events carrying a constitutive activation tag delineated by the maize dissociation (Ds) element, along with transposition frequency estimates of Ds delineated activation tag and enhancer-trap element induced upon stacking with a constitutive maize activator (Ac)-transposase cassette. To meet this goal we produced approximately 587 F1 Ac-stacks with the Ds-activation tag element and 144 F1 Ac-stacks with the Ds-enhancer trap element. Among 16 F2 derived populations from Ac X Ds-activation stacks we observed 26 unique germinal transpositions with an estimated 3.15% transposition frequency. Whereas among 22 F2 derived populations from the Ac X Ds-enhancer trap stacks only six unique germinal transpositions were detected, translating to an estimated 0.5% transposition frequency. Based on sequence data collected from junctions about the transposed Ds elements it appears that in soybean, Ds quite frequently re-inserts at unlinked positions respective to its corresponding launch site. Two germinal mutants characterized, a Ds-enhancer trap and a Ds-activation tag, landed in the third intron of a putative cyclic nucleotide binding domain gene, and a predicted IMP/GMP specific nucleotidase, wherein the former resulted in a reduction in tagged transcript accumulation, while the latter lead to miss-expression of the tagged gene.
2012-05-08T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/52
https://digitalcommons.unl.edu/context/agronhortdiss/article/1055/viewcontent/Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
transposon
Ac (activator)
Ds (dissociation)
activation tag
functional genomics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1057
2012-07-31T18:28:13Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MECHANISMS OF GROUP II INTRON LOSS FROM THE MITOCHONDRIAL <i>COX2</i> GENE OF PLANTS
Hepburn, Nancy J
It has been 35 years since the discovery of introns. Although fundamental aspects of their function and evolutionary origins have been widely studied, the mechanisms of intron loss are still an unresolved evolutionary mystery. Previously proposed mechanisms of intron loss include exonization, random genomic deletion and retroprocessing. The mitochondrial genomes of land plants have been characterized by widespread intron loss. In angiosperms, two introns located in the cox2 gene display a particularly variable intron distribution, indicating frequent loss. We took advantage of the frequent intron loss from cox2 to investigate the possible mechanisms of loss from this gene. The first study focused on Maganolia tripetala, a species that contains two cox2 gene copies that differ in intron content. Transcriptional and phylogenetic analyses indicated that the edit site distribution was not consistent with the retroprocessing model. Instead, we showed that the loss of two group II introns from the mitochondrial cox2 gene of Magnolia tripetala was mediated by a novel mechanism involving horizontal gene transfer and gene conversion (HGT-GC). In a broader study involving all angiosperms, we found no support for intron loss via exonization and random genomic deletion. We also did not find strong evidence supporting retroprocessing as the sole mechanism of intron loss. Our overall findings suggest that HGT-GC or an unidentified mechanism plays a larger role in the loss of introns than previously recognized.
Adviser: Jeffrey P. Mower
2012-07-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/54
https://digitalcommons.unl.edu/context/agronhortdiss/article/1057/viewcontent/NancyJH_THESISFINAL2.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
intron loss
horizontal gene transfer
gene conversion
retroprocessing
Magnolia tripetala
cytochrome oxidase subunit 2
Life Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1058
2012-08-02T01:30:53Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Identification of Stem Rust Resistance in Three Synthetic Wheat Populations
Ward, Russell A
Wheat stem rust incited by Puccinia graminis Pers.:Pers. = P. graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn is a major disease of wheat, with the potential to cause severe losses every year, hence making breeding for resistance important. For this project, two resistant synthetic wheat lines were studied using populations consisting of susceptible and resistant lines to determine the genetic basis of their stem rust resistance. Goodstreak has one dominant and one recessive resistance gene. Synthetics 303 and 370 each had two dominant genes present. For the Goodstreak/synthetic populations, testing F2 and F2:3 generations indicated the presence of three dominant genes and one recessive gene. To help identify individual genes, the synthetic lines were crossed to the cultivar ‘Lorikeet’ to test if the Ug99 resistance gene was Sr33, which is common in synthetic wheat lines, and the previously reported diagnostic marker Xcfd43 was used to test for the presence of Sr6 hypothesized to be in Goodstreak. The resistant synthetic lines did not contain Sr33, but Sr6 was in Goodstreak. We then postulated that the resistant lines contained one new Sr33-like Ug99 resistant gene and possibly Sr9e while Goodstreak contained Sr6 and an unknown gene. By identifying, postulating, and observing four resistance genes, these sources of resistance can be used and effectively incorporated in future cultivar improvement by wheat breeders to provide resistance to North American races of stem rust, as well as the Ug99 family of stem rust.
2012-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/55
https://digitalcommons.unl.edu/context/agronhortdiss/article/1058/viewcontent/RussellWard_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1059
2012-10-08T13:12:55Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
STUDIES OF DROUGHT TOLERANCE OF HARD RED WINTER WHEAT (<i>TRITICUM AESTIVUM </i> L.) CULTIVARS IN NEBRASKA
Bin Abdul Hamid, Sumardi
In Nebraska, about 75% of the wheat production is in the western half of the state, and about 92% of the winter wheat acreage is in dryland production, where productivity is limited by low and/or uncertain rainfall. We have investigated the effects of water stress on few established winter wheat (Triticum aestivumL.) cultivars, which are known for their superior adaptation to either rainfed or irrigated wheat production systems in western Nebraska. We also began a study to investigate the variation in the root system architecture to confer drought tolerance in winter wheat. The objectives of this study were to investigate the effects of water stress on root and shoot growth of winter wheat cultivars, and also to characterize the root system architecture (RSA) traits of winter wheat cultivars in order to evaluate their drought tolerance under limiting water conditions. The root length, root dry matter, root-to-shoot length ratio and root-to-shoot mass ratio of the three cultivars were significantly greater in the water stress than well-watered conditions. Results from the water stress experiment showed that Goodstreak is a drought tolerant cultivar due to its longest root length and high root dry matter. Based on the RSA phenotyping of the 3-week old water-stressed plants, Goodstreak had the highest total root length, total root length density, projected area of roots and network root length distribution. Under water stress conditions, Harry demonstrated a shallow root system with low root and shoot dry matters but displayed the highest root-to-shoot length ratio. It appeared that Harry utilized less water and invested less energy into dry matter under water stress. Our findings support the fact that Wesley performed well in irrigated wheat production systems in Nebraska because of its high shoot and root biomasses. This study leads us to suggest that Wesley is a drought sensitive cultivar because it uses the available soil moisture at ‘uneconomical’ and ‘unsustainable’ rate compared to Harry and Goodstreak.
Advisors: P. Stephen Baenziger and Harkamal Walia
2012-09-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/56
https://digitalcommons.unl.edu/context/agronhortdiss/article/1059/viewcontent/Sumardi_s_Final_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
drought
winter wheat
water stress
root phenotyping
drought tolerant
drought susceptible
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1060
2012-11-19T18:55:43Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Organellar Signaling Expands Plant Phenotypic Variation and Increases the Potential for Breeding the Epigenome
De la Rosa Santamaria, Roberto
MUTS HOMOLOGUE 1 (MSH1) is a nuclear gene unique to plants that functions in mitochondria and plastids, where it confers genome stability. Phenotypic effects of MSH1 down- regulation were studied in sorghum inbreed line Tx430 and Arabidopsis ecotype Columbia-0, with the hypothesis that RNAi suppression of MSH1 triggers retrograde signaling from organelles to the nucleus, alters the epigenome, and derives heritable phenotypic variation suitable for artificial selection. An array of morphological traits and metabolic pathways was detected, including leaf variegation, male sterility and dwarfism, associated with altered gibberellic acid metabolism, higher levels of reactive oxygen species (ROS), and decreased synthesis of ATP. A phenotype that combines dwarf, increased branching, reduced stomatal density and delayed flowering was identified, and designated developmental reprogrammed (MSH1-dr). Reproducible in additional plant species, this phenotypic variation is partially reversed by exogenous GA. In sorghum, the phenotype displays complete penetrance under self-pollination, even after segregation of the transgene, whereas progeny of MSH1-dr transgene null plants x wildtype Tx430 display enhanced growth. Significant differences for agronomic traits and response to selection were observed in the tested F2 to F4 generations, with mean values that surpass the wildtype up to 70% for grain yield/panicle and plant height, and 100% for biomass yield/plant. SSR marker analyses among the parental phenotypes Tx430 and MSH1-dr transgene null, and their derived lines, show no polymorphism, suggesting that the observed changes are non-genetic. In Arabidopsis, this enhanced growth is accompanied by genome methylation changes, whereas genetic hemi-complementation indicates that the novel phenotype results from chloroplast disruption.
Adviser: Sally A. Mackenzie
2012-10-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/57
https://digitalcommons.unl.edu/context/agronhortdiss/article/1060/viewcontent/Roberto_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Epigenetics
Plant Breeding
MutS Homolog1
Organellar Signaling
Agriculture
Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1061
2012-12-04T22:24:48Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Improved Understanding of Factors Influencing the Re-emergence of Goss's Bacterial Wilt and Blight of Corn
Langemeier, Craig B.
Goss’s bacterial wilt and blight (Goss’s wilt) is a serious and sometimes severe disease of corn. Goss’s wilt was first identified in Dawson County Nebraska in 1969. Today Goss’s wilt can be found in two countries including the U.S. and Canada, and twelve states including Nebraska, Iowa, North Dakota, South Dakota, Minnesota, Illinois, Indiana, Texas, Kansas, Colorado, Wisconsin and Wyoming. Goss’s wilt was observed in Nebraska throughout the 1970’s, and from the early 1980’s until recently developed only sporadically. Around 2006, a re-emergence of the disease was observed in western Nebraska, northeast Colorado, and southeast Wyoming. Since then, reports of the disease have been rapidly increasing north, south, and east, and has been reported across the entire Corn Belt. A survey was implemented to determine what agronomic and environmental factors may be contributing to this development and increased incidence in corn growing regions of the U.S. The survey showed that the Goss’s wilt rating assigned by seed companies, planting population density, planting date in 2011, crop rotation, and percent crop residue cover were all important factors to whether or not a field tested positive to Goss’s wilt. A second study was implemented to determine if the bacterial pathogen had genetic differences based on geographical origin. The study used amplified fragment length polymorphism (AFLP) and a box polymerase chain reaction (BOX-PCR) to separate isolates based on differences in DNA banding patterns. The study concluded that Cmn isolates were genetically similar across the entire sampling region, and isolates with similar banding patterns could be found in all states included in the survey. A third study was implemented to test if alternate hosts of the pathogen may be playing a role in the dissemination and survival of the pathogen. Results from the study indicate that three species of foxtail were alternate hosts to Cmn. These included yellow, giant, and bristly foxtail. These results will help producers better manage and potentially prevent Goss’s wilt in the future.
Advisors: Tamra Jackson-Ziems, Greg Kruger
2012-11-28T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/58
https://digitalcommons.unl.edu/context/agronhortdiss/article/1061/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Goss's Wilt
Plant Pathology
oai:digitalcommons.unl.edu:agronhortdiss-1062
2012-12-06T20:20:14Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Nitrous Oxide Emissions from Smooth Bromegrass Pasture under Nitrogen Fertilizer and Ruminant Urine Application in Eastern Nebraska
Snell, Laura K
Nitrous oxide (N2O) is a greenhouse gas primarily produced in soils by denitrifying and nitrifying organisms. Agricultural soils account for 70% of emissions in the United States, but little data is available for contributions from managed pasture ecosystems. This study focused on the production of N2O in smooth bromegrass (Bromus inermis Leyss.) pastures established on silt loam soils in eastern Nebraska. Thirty smooth bromegrass plots (1.5m x 1.5m) were treated with five different fertilizer treatments (0, 45, 90, 135, and 180 kg N/ha) and two urine treatments (urine and no urine). Herbage sampling was taken the day before sampling by clipping the grass within the anchor to a 10 cm stubble height and oven drying the samples. In 2011, a significant effect between the urine treatment x fertilizer rate and cumulative herbage yield (p = 0.0002) was found. In 2012, the urine treatment significantly affected cumulative herbage yield (p < 0.0001). In 2011, cumulative herbage yield increased with total nitrogen inputs of up to 675 kg N ha-1 compared with 435 kg N ha-1 in 2012. N2O emissions were recorded biweekly from March to October using the Hutchinson and Mosier (1981) vented chamber method in 2011 and 2012. Findings revealed a significant interaction between urine treatment x fertilizer rate interaction and cumulative seasonal flux (p = 0.0061) in 2011 and the urine treatment (p < 0.0001) in 2012. There was a significant exponential relationship between fertilizer rate and cumulative seasonal flux in respect of urine treatment in 2011 (p2O was between 0.518-1.781% for treatments in 2011 and 0.126-0.395% in 2012. The research supports the IPCC recommendations of 1.25% +/- 1% applied N lost as N2O.
Advisor: John A. Guretzky
2012-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/60
https://digitalcommons.unl.edu/context/agronhortdiss/article/1062/viewcontent/Laura_Snell_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
carbon budgeting
global warming potential
denitrifying
nitrifying
Bromus inermis Leyss
Agricultural Science
Agriculture
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1063
2016-09-08T19:26:52Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Environmental Triggers of Winter Annual Weed Emergence and Management to Reduce Soybean Cyst Nematode Reproduction on Winter Annual Weed Hosts
Werle, Rodrigo
Winter annual weeds are becoming more common in many row crop fields in the midwestern USA. The impact of winter annual weeds in cropping systems is often overlooked because these weeds complete their lifecycle near the time of crop sowing. However, delayed soil warming, competition for nutrients during initial establishment of the main crop, difficult planting operations, and yield loss are some of the problems caused by dense mats of winter annual weeds. Moreover, some of these weeds have been reported as alternative hosts for pests such as the soybean cyst nematode (Heterodera glycines, SCN), considered the most important soybean pathogen in the USA. Research looking at the effect of time of herbicide application on SCN development on weed hosts has not been reported. Thus, our first objective was to evaluate how the development of SCN on henbit roots was affected by time of herbicide application and herbicide mode of action. The results of this research indicated that early management of henbit plants can significantly reduce SCN reproduction potential in the absence of its main host, soybean. In order to better manage weeds, it is important to know when they will emerge, since weeds are easily controlled during early stages of growth. The emergence pattern of winter annual weeds common to the midwest region of the United States has not been reported. Therefore, our second objective was to understand and predict emergence of winter annual weed species using models based on the accumulation of modified thermal/hydrothermal time. The results of this research indicated that soil temperature was the main factor driving winter annual weed emergence. According to our findings, the majority of the winter annual weeds will emerge by late-fall in Nebraska, indicating that, as long as environmental conditions are adequate for herbicide application or mechanical cultivation, this would be the ideal time to manage these weeds. These results may help farmers to better manage winter annual weeds.
Adviser: John L. Lindquist
2012-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/59
https://digitalcommons.unl.edu/context/agronhortdiss/article/1063/viewcontent/Werle_2012_MS_Agronomy.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agronomy and Crop Sciences
Other Plant Sciences
Plant Pathology
oai:digitalcommons.unl.edu:agronhortdiss-1064
2012-12-13T20:48:07Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Ecology and invasive properties of musk thistle (<i>Carduus nutans</i>) in the Central Prairies of Nebraska
Han, Chengchou
Musk thistle (Carduus nutans) is an herbaceous monocarpic herb introduced to the U. S. from Eurasia. The invasion of musk thistle can reduce forage area, soil stability, and reduce recreation and open areas for humans and wildlife.
Resistance of warm season and cool season perennial grass communities to musk thistle invasion is important for land managers to consider, especially where disturbance has made an area particularly susceptible. Our results show that disturbances, such as overgrazing can open up niches in canopies of warm season grass communities and facilitate invasion but not in cool season grass communities. The mechanism of invasion by musk thistle may depend on an overlap in the timing of resource use patterns by the invader and perennial grass communities. Our results showed that an undisturbed (e.g., non-grazed, normal precipitation) stand of warm season perennial grasses can suppress the establishment of musk thistle by restricting the amount of light that reaches the soil surface. A disturbance of extreme drought creates more niches in warm season perennial grass communities (e.g., reduced growth), but newly germinating musk thistle plants cannot compete for the reduced amount of soil moisture. High disturbance (e. g., grazing) allowed extensive amounts of light to penetrate into overgrazed warm season perennial grass communities, which facilitated the successful invasion by musk thistle. In cool season perennial grass communities, light is less critical, regardless of soil moisture.
The unsuccessful invasion of musk thistle into cool season perennial grass communities is most likely due to grass root phenology and distribution (88 m m-2). Root growth and development and distribution patterns should be taken into account for effective perennial grass restoration in areas with high risk from invasive plant species.
The ecology of musk thistle seed suggests germination is strongly influenced by temperature, light, moisture, salinity, dormancy and habitat types and should be factored into an integrated invasive plant management plan that targets early growth of musk thistle seedlings.
Advisor: Stephen L. Young
2012-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/61
https://digitalcommons.unl.edu/context/agronhortdiss/article/1064/viewcontent/Chengchou_Han_2012_Ecology_and_invasive_properties_of_musk_thistle__Carduus_nutans__1.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Carduus nutans
cool season perennial
germination
invasion
musk thistle
warm season perennial
Agricultural Science
Agronomy and Crop Sciences
Ecology and Evolutionary Biology
Plant Biology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1065
2013-04-30T18:34:14Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Response of Nebraska Horseweed (<i>Conyza canadensis</i>) Populations to Dicamba
Crespo, Roberto
Bernards, Mark L
Kruger, Greg
Lee, Donald
Wilson, Robert, Jr.
Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism-of-action for postemergence weed control in soybean. Numerous broadleaf species, including horseweed, have evolved resistance to glyphosate. It is anticipated that dicamba will be used by farmers as a primary tool to manage these weeds. Studying and understanding variability in horseweed response to dicamba will aid in developing appropriate risk management strategies to extend the utility of the dicamba-resistance technology. Horseweed plants from ten Nebraska populations were treated with one of nine doses of dicamba in greenhouse experiments. At 28 days after treatment (DAT) visual injury estimations were made and plants were harvested to determine dry weight. There was a three-fold difference in the I90 (90% visual injury estimate) between the least (638 g ha-1) and most (205 g ha-1) susceptible populations. Two plants from five populations were observed for an additional three months. No plants treated at doses above 280 g ha-1 survived to set seeds. These results suggest that maintaining use doses of 560 g ha-1 or greater may fully control horseweed populations from Nebraska and minimize the risk of plants surviving to set seed, in addition to practicing other proven herbicide-resistance management strategies.
2013-04-15T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/62
https://digitalcommons.unl.edu/context/agronhortdiss/article/1065/viewcontent/Crespo_JAS_2013_Response_Nebraska_Horseweed.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Canada fleabane
dose-response
herbicide resistance
marestail
risk assessment
Agricultural Science
Agronomy and Crop Sciences
Horticulture
Other Plant Sciences
Plant Biology
oai:digitalcommons.unl.edu:agronhortdiss-1066
2020-05-18T19:20:15Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
APPLICATION CARRIER VOLUME: A COMPREHENSIVE EVALUATION OF AN ULTRA-LOW VOLUME SPRAYER COMPARED TO A CONVENTIONAL SPRAYER FOR ROW-CROP AND TURFGRASS PRODUCTION SYSTEMS
Ferguson, Jason Connor
An Ultra-Low Volume (ULV) sprayer was developed to decrease carrier volume required for pesticide applications in row and turfgrass cropping systems. The ULV sprayer can make spray applications at or below 19 L ha-1, which is far lower than a conventional sprayer in row crop or turfgrass production systems. Field studies were conducted at the University of Nebraska West Central Research and Extension Center Dryland Farm near North Platte, NE and the John Seaton Anderson Turfgrass Research Facility near Mead, NE to compare the ULV sprayer to a conventional sprayer. Studies were conducted to compare the two sprayers with herbicide applications, fungicide applications, and foliar fertilizer applications.
The row crop studies were applied over plots planted to six different species. Plant species used were non-glyphosate-resistant corn (Zea mays L.), non-corn glyphosate-resistant soybeans (Glycine max (L.) Merr.), amaranth (Amaranthus hypochondriacus L.), quinoa (Chenopodium quinoa Willd.), velvetleaf (Abutilon theophrasti Medik.), and green foxtail (Setaria viridis (L.) Beauv). Each of these species were harvested and dried to compare dry weight reductions from the herbicide applications. The row crop studies were conducted in the summer of 2011 and the summer of 2012. The row crop studies also compared droplet size and distribution on a laser diffraction instrument to correlate droplet size and efficacy in the comparison of the two sprayers. In general the ULV sprayer had a different droplet spectrum from the conventional sprayer, but differences in the droplet size did not reveal a difference in the dry weight reductions across the row crop studies over both years.
The turfgrass studies were conducted in one of three different turfgrass systems: a mixed stand of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.); a uniform stand of tall fescue (Festuca arundinacea Schreb.); or a creeping bentgrass ‘L-93’ (Agrostis stolonifera L.) system managed to fairway height. The turfgrass studies were conducted in the spring and summer of 2012. Differences were not observed between the two sprayers across all of the turfgrass studies.
The ULV sprayer appears to be a useful option for a variety of spray applications in row crop and turfgrass production systems.
Adviser: Greg R. Kruger
2013-05-06T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/63
https://digitalcommons.unl.edu/context/agronhortdiss/article/1066/viewcontent/APPLICATION_CARRIER_VOLUME___Connor_Ferguson_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Application Technology
Droplet Size
ULV
Adjuvant
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1067
2013-08-07T16:03:12Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Ammonia and Nitrous Oxide Loss from Sprinkler Applied Beef Feedlot Effluent
McAfee, Blythe P
A range of flux chambers are available and have been used to measure fluxes of atmospheric gases, including NH3, with the addition of acid traps. Previous studies show acid traps can be very effective but there is a need to understand how chambers affect acid trap efficiency so measurements can be adjusted for more accurate results. In this lab study, chamber tightness, pump flow variation, and NH3 trapping efficiency of a flux chamber system were examined. Chamber leakage varied with time from 1-7%. Pumping rate between pumps was significantly different and when included in the closed chamber system, pump rate was reduced on average by 43.8 ± 0.598%. Compared to the acid bubbler trap alone (Woodbury et al., 2006), the trapping efficiency of the acid trap-chamber system was lower and varied with the mass of NH3 emitted. Chamber tightness and pump flow rate also contribute to overall chamber efficiency, with pump flow rate having the greatest effect of all parameters examined. These findings were used to improve a mass-based model for calculating NH3 trapping efficiency of the system. The model predicts the mass and percentage of NH3 collected from the flux chamber system based on the varying of different chamber input parameters. The model can be used to estimate trapping efficiency of chambers, or be used to calculate and adjust previous NH3 measurements taken with this closed flux chamber system. The model was utilized to estimate NH3 fluxes from the following study on sprinkler application of beef feedlot effluent.
Loss of nitrogen from sprinkler applied beef feedlot effluent can be costly for both the producer and the environment. Sprinkler application of effluent is common throughout the Great Plains, though little work has occurred focusing specifically on N losses from beef feedlot effluent. The objectives of two studies were to quantify NH3 and N2O losses from beef feedlot effluent applications under field conditions and determine the effects of soil pH, percent water filled pore space, NH4+ concentration of the effluent, and weather conditions on NH3and N2O. Nitrogen losses during application were determined from the differences between NH4+-N concentration of samples taken under the sprinklers and samples taken from the effluent. NH3-N and N2O emission following application were measured using a closed chamber technique with a recirculating configuration and acid traps. In the first study, sprinklers were protected from the wind and NH4+-N losses[1] during application were not seen. Average rate losses from a second study, with no protection against wind and a mean wind speed of 15 m s-1, accounted for 55% of the effluent NH4+-N from drift beyond collection jars during sprinkler application. Following application, N losses from both volatilization and N2O emissions from soil were less than[2]1% of the original effluent NH4+-N concentration. Soil pH and effluent NH4+-N concentration did not significantly affect the percent of N lost. Increasing wind speed and air temperature resulted in greater N losses during application. Weather factors including: soil temperature, air temperature, %WFPS, and relative humidity had varying effects on NH3 and N2O emissions following application.
Advisor: Charles S. Wortmann
2013-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/64
https://digitalcommons.unl.edu/context/agronhortdiss/article/1067/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
flux chambers
GRACEnet
trapping efficiency
effluent
ammonia volatilization
Nebraska
nitrous oxide emission
soil pH
weather
Agriculture
oai:digitalcommons.unl.edu:agronhortdiss-1068
2013-08-13T17:38:30Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MULTIFACTORIAL ANALYSIS OF MORTALITY OF SOYBEAN CYST NEMATODE (<i>Heterodera glycines</i> Ichinohe) POPULATIONS IN SOYBEAN AND IN SOYBEAN FIELDS ANNUALLY ROTATED TO CORN IN NEBRASKA
Perez-Hernandez, Oscar
The soybean cyst nematode (SCN; Heterodera glycines Ichinohe) is the most economically important pathogen of soybean in the U.S. The effect of annual corn rotation, soil properties, weather, and agronomic factors on SCN population densities was quantified in 45 fields in Nebraska over three years. SCN population densities (eggs/100 cm3 of soil) in each field were determined before (Pi) and after (Pf) annual corn rotation. Average SCN population density reduction was 50.62%. Multivariate analysis was used to describe the relationship of soil texture (% of sand, silt, and clay), Pi, and Pf. Two principal components explained 92% of the variability in the data set. The first component was represented by texture and accounted for 60.5% and the secondwas represented by Pi and Pf and explained 31.5%. Cluster analysis identified two groups of fields: one group with predominantly sandy soil (57 to 95%) and the other with predominantly silty soil (23 to 61%). SCN Pi was significantly higher in the sandy group than in the silty group (F = 271.19, P
The SCN Pf was modeled using an initial set of eight predictors. A negative binomial regression model with the log link function was applied to a 35-field training data set and a final model was selected. This model was used to estimate the nematode population density after annual corn rotation in the training data set and its prediction power was 82.1%. This predicting capability was confirmed in a validation data set in which the model’s predicting capability was 79.6%.
Intra and interplot spatial variability of SCN population densities was analyzed in three experimental areas and its relationship with soybean yield was examined. SCN population densities had an aggregated pattern, showing spatial dependence with those of adjacent plots. The β-binomial distribution adequately described data of incidence and suggested that SCN population density aggregation also occurred within plots. The SCN reproduction factor was not related to the number of SCN-positive cores per plot nor was it related to soybean yield in two soybean varieties assessed, one resistant and one susceptible.
Advisor: Loren J. Giesler
2013-08-05T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/65
https://digitalcommons.unl.edu/context/agronhortdiss/article/1068/viewcontent/PhD_Dissertation_whole_document.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
soybean cyst nematode
modeling
corn rotation
Plant Pathology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1069
2013-08-16T17:44:09Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
High Yield Soybean Management: Planting Practices, Nutrient Supply, and Growth Modification
Sonderegger, Evan
Growers are constantly seeking ways to improve yield in soybean [Glycine max (L.) Merr.]. There has been much interest in the use of selected alternative practices to maximize soybean yield. These practices include planting soybean at higher than recommended seeding rates, planting soybean in narrow rows, breaking apical dominance to induce branching, application of strobilurin fungicides prophylactically to minimize disease and extend the seed filling period, the use of N fertilizer both in furrow and foliar applied, and the use of seed treatments to promote early stand establishment and health. Field studies were conducted at the University of Nebraska West Central Research and Extension Center in North Platte, Nebraska, and at the West Central Water Research Field Laboratory located near Brule, Nebraska and at Bancroft, Clay Center, Cortland, and Elba, Nebraska to determine how these practices affect soybean yield.
Increased seeding rate also increased soybean yield and 24.7, 43.2, and 61.8 planted seeds m-2 yielded 4.47, 4.79, and 4.79 Mg ha-1, respectively. Soil fertility, application of strobilurin and seed treatments did not affect yield. Decreases in yield were observed by destroying the apical meristem by both clipping at V2 and application of lactofen.
These results suggest that soybean yield is optimized in west central Nebraska by planting soybean at between 24.7 and 43.2 seeds m-2 but not applying lactofen or pyraclostrobin. Growers should be very careful in selecting alternative practices due to the possible reduction in soybean yield.
Advisors: Greg R. Kruger and Charles S. Wortmann
2013-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/66
https://digitalcommons.unl.edu/context/agronhortdiss/article/1069/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Soybean
Nitrogen
Population
Lactofen
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Horticulture
Plant Biology
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1070
2013-09-18T19:04:08Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
A Study of the Historical Development and Horticultural Practices of a Public Garden
Nosal, Steven J.
This project examined the historical development and the horticultural practices in the public gardens of the Parks Department in Lincoln, Neb. It concentrates on one particular place to illustrate development and practice issues: the Sunken Gardens. This garden was built during the Depression in the 1930s as a place of beauty for all of the citizens of Lincoln. Although the Sunken Garden covers only 1.5 acres, it has remained a very important part of Nebraska's capital city for more than 64 years.
2013-09-16T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/67
https://digitalcommons.unl.edu/context/agronhortdiss/article/1070/viewcontent/Nosal_1994_Hort_thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Trans-Mississippi Exposition
City Beautiful Movement
Lincoln NE
Sunken Gardens
Antelope Park
Philip Edinborough
George Goebel
Henry Goebel
oai:digitalcommons.unl.edu:agronhortdiss-1071
2016-09-08T19:34:05Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Biology and Control of Common Purslane (<i>Portulaca oleracea</i> L.)
Proctor, Christopher A.
Common purslane (Portulaca oleracea L.) is a summer annual with wide geographic and environmental distribution. Purslane is typically regarded as a weed in North America, but it is consumed as a vegetable in many parts of the world. One of the characteristics that make purslane difficult to control as a weed is its ability to vegetatively reproduce. Severed sections of purslane stem containing a node will produce adventitious roots from the cut end of the stem. Isoxaben and simazine were the only two effective preemergence herbicides for controlling purslane in our studies when applied at maximum or one-half maximum label rates. Of the 25 postemergence herbicides evaluated, fluroxypyr, triclopyr, dicamba, and metsulfuron-methyl were the most effective for controlling purslane. Purslane’s ability to adapt to a broad range of environmental conditions is due, in large part, to its unique photosynthetic metabolism. Under well-watered conditions, purslane utilizes C4 photosynthetic metabolism. However, purslane will shift to a CAM-like photosynthetic metabolism under droughty conditions, with nocturnal acid accumulation in the leaves and reduced CO2 uptake. Phosphoenolpyruvate carboxylase (PEPC) catalyzes the initial step in photosynthetic fixation of atmospheric CO2 in C4 and CAM plants. Regulation of PEPC is primarily via phosphorylation by PEPC kinase (PEPCK). For well-watered purslane, PEPC and PEPCK transcript abundance are indicative of C4 metabolism, but in water-stressed purslane, PEPCK transcripts accumulate at night suggesting a shift in the phosphorylation pattern of PEPC to CAM-like metabolism. By understanding purslane’s unique photosynthetic metabolism, we can gain insight into how it effectively adapts to water limiting environments.
2013-09-09T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/68
https://digitalcommons.unl.edu/context/agronhortdiss/article/1071/viewcontent/Proctor_Thesis_9_17_13_Final.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
stress physiology
phosphoenolpyruvate carboxylase
herbicide control
vegetative reproduction
Agronomy and Crop Sciences
Plant Biology
oai:digitalcommons.unl.edu:agronhortdiss-1072
2013-12-05T16:32:08Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Changes in <i>Poa annua</i> Populations in Response to Herbicides and Plant Growth Regulators
Brown, Jesse
Poa annua (annual bluegrass; ABG) is an invasive weedy species in turfgrass. Herbicides and plant growth regulators (PGRs) are often used for ABG control, providing limited or inconsistent results. Identifying shifts in ABG populations in response to these treatments would be beneficial for understanding inconsistent control. Our research employed amplified fragment length polymorphic (AFLP) markers with the objective to determine if there are changes in genetic structure of ABG populations after multiple-year season-long control programs in three states. Annual bluegrass was sampled after the second or third year of seven different season-long ABG treatments consisting of herbicide or PGR applications. The trials were conducted at three different locations (East Lansing, Michigan; West Lafayette, Indiana; Lincoln, Nebraska). In the ABG samples, AFLP markers were identified for each site and 649, 745, and 762 were produced for Michigan, Indiana and Nebraska, respectively. Population analysis was conducted in Structure and identified five distinct ABG populations in Michigan, seven in Indiana, and six in Nebraska. Season-long treatments of trinexapac-ethyl or bispyribac-sodium (bispyribac) at a low rate effected genetic structure of populations at all locations. However, ABG populations that were affected by an individual herbicide or PGR did not respond consistently among locations. Bispyribac treatments increased ABG population variability in Michigan, but decreased variability in Indiana and Nebraska. Trinexapac-ethyl treatments decreased ABG population variability in Michigan and Indiana, but increased variability in Nebraska. This study provides a genetic basis in understanding how herbicides or PGRs impact ABG populations over the long term and our results may help explain inconsistencies in chemical control of ABG.
Advisors: Keenan Amundsen and Zac Reicher
2013-12-02T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/69
https://digitalcommons.unl.edu/context/agronhortdiss/article/1072/viewcontent/Thesis_12_2_13.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
annual bluegrass
population dynamics
herbicides
plant growth regulators
Agriculture
oai:digitalcommons.unl.edu:agronhortdiss-1073
2019-12-05T15:03:28Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Positioning an Innovative Flame-weeding Technology Into Crop Production
Stepanovic, Strahinja V
Propane flaming has a potential to be utilized for effective PRE and POST weed control in both organic and conventional farming systems. Field studies were conducted at the Haskell Agricultural Laboratory of the University of Nebraska in 2010, 2011, and 2012 to: (1) describe dose–response curves for propane when flaming selected weed species at different growth stages, (2) determine corn and soybean tolerance to single and repeated flaming by utilizing the equipment designed to selectively flame weeds in row crops with torches positioned parallel to the crop row, and (3) determine the effectiveness of flaming and cultivation for weed control management under two manure levels in organic corn and soybean. Results from these studies indicate that single application of broadcast flaming can be adjusted to effectively control tansy mustard, henbit, and common lambsquarters and temporary suppress of cutleaf evening primrose, field pennycress, and dandelion. Hood technology on four-row flamer protected the major portion of the leaves from any heat damage, thus minimizing crop injury when flaming was conducted at V5 stage of soybean and V4 and V6 stages of corn. Results suggest that that both corn and soybean were able to tolerate up to two flaming operations with propane dose of 45 g ha-1 without any yield reduction; but, for best results, soybeans should be flamed at VC and after V4-V5, while timing of flaming in corn is less critical. Combination of banded flaming and between row cultivation applied twice in the season was the most effecting weed control treatment in both corn and soybean. Same treatment is some cases yielded statistically similar to weed-free control and compared to cultivation twice there was a significant improvement in weed control efficacy. Alternatively, broadcast flaming could be employed to provide satisfactory weed control when conditions are too wet to cultivate. Flaming should be combined with cultivation and other non-chemical weed control practices to increase overall effectiveness of weed management programs.
Adviser: Stevan Knezevic
2013-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/70
https://digitalcommons.unl.edu/context/agronhortdiss/article/1073/viewcontent/M.S._THESIS___Strahinja_Stepanovic___final_version_3.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
organic farming
flame-weeding
mechanical cultivation
dose-response
crop injury
weed control
yield
yield components
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1074
2014-02-20T20:46:48Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MODIFYING THE FATTY ACID PROFILE OF SOYBEAN OIL FOR
NUTRITIONAL AND INDUSTRIAL APPLICATIONS
Park, Hyunwoo
The objectives of this study are: 1. To develop of soybean oil low in palmitic acid and elevated in stearic and oleic acids for margarine source. 2. To produce the high omega-3 fatty acid and astaxanthin in soybean seed as a feedstock for aquaculture. Over expression of mangosteen stearoyl-ACP thioesterase gene increased stearic acid content up to 10% to 15%. The identified elevated stearic acid events were crossed with our high oleic acid/low palmitic acid event. Average stearic and oleic acid content ranged 14 to 19% and 68 to 73% respectively. Stearic acid content of elevated stearic acid soybean event and cross line was stable over generation. However, in generation six and seven under field conditions the oleate levels decreased to 30-40%.
Decline of marine fish stocks due to over-fishing and the use of wild fish for diets of farmed fish pushed for development of sustainable land based alternative diets for farming fish such as soybean with respect to levels of very long chain omega-3 fatty acids, EPA and DHA. To generate EPA and the high value carotenoid, astaxanthin in soybean, we first created a two gene stack in soybean combining Δ6 and Δ15 desaturase genes, respectively. The resultant event designated 535-9 accumulates stearidonic acid in seed oil up to 35%. We have subsequently generated transgenic events that carry Δ6 elongase and Δ5 desaturase genes. Selected events derived from the latter have been crossed with event 535-9. EPA level in seed oil was up to 4%. In regards to astaxanthin production, we generated transgenic event carrying phytoene synthase, crtZ and crtW genes. Transgenic soybean produced up to 25μg/g astaxanthin. We crossed the four-gene EPA stack with the three gene astaxanthin stack to create a prototype soybean-based feedstock for aquaculture. We identified that the longer chain omega-3 fatty acids ETA and EPA, combined ranged from approximately 3-5% of the oil, along with astaxanthin and β-carotene accumulation from 23 to 44.8 μg/gr and 527 to 1139 μg/gr seed, respectively.
2012-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/71
https://digitalcommons.unl.edu/context/agronhortdiss/article/1074/viewcontent/Hyunwoo_Park_2012.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1075
2014-04-23T15:33:31Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Delay of Bud Break on 'Edelweiss' Grapevines with Multiple Applications of Amigo Oil and NAA
Loseke, Benjamin A
‘Edelweiss’ is an important grape cultivar grown in the Midwestern part of the USA. This grapevine is tolerant to extreme winter temperatures which can be experienced in the areas where it is most widely grown. ‘Edelweiss’ is one of the earliest cultivars in the vineyard to break bud, making it very susceptible to late spring freezes. The primary buds of ‘Edelweiss’ produce a significant amount of fruit, while unlike many other hybrids, the secondary and tertiary buds will have little to no yields, thus making it important to protect the primary buds from a late freeze. The objective of this research was to determine if multiple applications of Naphthaleneacetic acid (NAA) or Amigo Oil has a greater effect on bud delay when compared to single applications. ‘Edelweiss’ vines were treated with one, two, or three applications of NAA or Amigo Oil at monthly intervals starting in early January. The purpose of the Amigo Oil and NAA application was to delay bud break without affecting desired characteristics such as yield or fruit composition. Amigo Oil was applied at 10% concentration (v/v) and the NAA at 1000 ppm with a custom built all-terrain vehicle (ATV) sprayer. All treatments of Amigo Oil led to a significant bud break delay ranging from 3 to 11 days as compared to the control. None of the treatments resulted in negative effects on yield or fruit characteristics. A controlled laboratory experiment was also conducted, where single bud cuttings were forced in forcing solution containing 200 ppm 8-hydroxyquinoline citrate and 2% sucrose at 25°C under 12 hour days. Treatments of one, two, or three applications of 1000 ppm NAA and 10% (v/v) Amigo Oil were applied to single buds at weekly intervals. Julian days until bud break were recorded and treatment-related bud break delays were observed. Two and three applications of oil significantly delayed bud break ranging from 14 to 24 days. All NAA treatments led to significant bud delay ranging from 6 to 9 days. Grape growers in climates with the potential of late spring freezes may consider the use of Amigo Oil as a potential means to protect their vines from freeze injury.
Advisor: Paul E. Read
2014-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/72
https://digitalcommons.unl.edu/context/agronhortdiss/article/1075/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Naphthaleneacetic Acid
Dormant Oil
Bud Break
Freeze
Grapevine
Viticulture and Oenology
oai:digitalcommons.unl.edu:agronhortdiss-1076
2014-04-29T00:17:11Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
A Regional Investigation of In-season Nitrogen
Requirement for Maize Using Model and Sensor-based Recommendation Approaches
Stevens, Laura J
N management for corn can be improved by applying a portion of the total N during the growing season, allowing for adjustments responsive to actual field conditions. This study was conducted to evaluate two approaches for determining in-season N rates: Maize-N model and active crop canopy sensor. Various sensor algorithms designed for making in-season N recommendations from crop canopy sensor data were evaluated. The effects of corn hybrid and planting population on recommendations with these two approaches were considered. In a 2-yr study, a total of twelve sites were evaluated over a 3-state region, including sites in Missouri, Nebraska, and North Dakota. In-season N recommendations were generally lower when using the sensor-based approach with Holland and Schepers (2012) algorithm than the model-based approach. This resulted in observed trends of higher partial factor productivity of N and agronomic efficiency for the sensor-based treatments. At specific sites, conditions leading to high levels of mineralized N becoming available to the crop during the growing season increased environmental and economic benefit of the sensor-based approach. The optimum N rate was estimated using a linear-plateau model. Compared to the sensor-based approach with the Holland and Schepers algorithm, the model-based approach more closely estimated the optimum N rate and erred by over-recommending N. Profit loss from the sensor with Holland and Schepers algorithm was greater when considering all sites collectively due to the greater cost of lost yield when N was under-applied, versus the lower cost of excess N when N was over-applied.
Adviser: Richard B. Ferguson
2014-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/73
https://digitalcommons.unl.edu/context/agronhortdiss/article/1076/viewcontent/Thesis_Laura_Stevens.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Precision Agriculture
Site-specific Crop Management
Maize-N Model
Crop Canopy Sensor
Optimum N Rate
Sensor Algorithms
corn
Agronomy and Crop Sciences
Soil Science
oai:digitalcommons.unl.edu:agronhortdiss-1077
2014-04-29T00:27:48Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Population Dynamics of Triticum Mosaic Virus in Various Host Species
Bartels, Melissa S
It has been established that RNA viruses should be genetically diverse, due to the high error rate of their RNA-dependent RNA polymerases and the lack of proof-reading capabilities. Plant RNA viruses are not as genetically diverse as expected. Evolutionary factors, such as purifying selection and bottlenecks that favor genetic stability, might be affecting plant viral populations. Otherwise RNA virus populations, with their potential for extreme diversity, might acquire a lethal number of mutations leading to the collapse of the population.
Triticum mosaic virus (TriMV) populations maintained in a controlled greenhouse environment displayed genetic stability. The mutation frequency per nucleotide of TriMV protein 1 (P1) and coat protein (CP) cistrons was discovered to be half that of similar plant viruses. Variations within serial passaged TriMV populations were dominated by singletons within both cistrons examined. Thus, stochastic processes such as bottlenecking are impacting the populations observed. The founding inoculum type sequence was preserved throughout the serial passages therefore some level of genetic stability was being maintained.
The mutation frequencies observed within the CP cistron of two TriMV isolates within wheat, rye, barley, and triticale, were not significantly different, suggesting that the level of TriMV population diversity is maintained across these hosts. The lack of preference for any particular host examined suggests that both TriMV isolates are equally adapted. The variation of the P1 and CP regions of TriMV populations, horizontally transmitted by wheat curl mites, were determined. The alternative host, jointed goatgrass, caused no shift from the founding haplotype of the P1 or CP within the TriMV populations observed, indicating that the bottlenecks occurring within this host are similar to those within wheat. TriMV populations maintain genetic stability, even with the constraints of genetic bottlenecking by horizontal transfer by wheat curl mites.
The TriMV populations observed maintained genetic stability by the evolutionary forces of selection and genetic bottlenecking. This leads us to conclude that selection and drift are not exclusive, and may occur concurrently within a virus population. This research shows that the combined effect of both forces acting simultaneously on different regions of the genome ultimately regulates the degree of sequence variation within virus populations.
Advisor: T. Jack Morris
2014-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/74
https://digitalcommons.unl.edu/context/agronhortdiss/article/1077/viewcontent/Melissa_Bartels_PhD_dissertation.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Triticum Mosaic Virus
plant virus
wheat
bottlenecks
Agronomy and Crop Sciences
Plant Pathology
Virology
oai:digitalcommons.unl.edu:biosysengdiss-1044
2014-07-03T21:58:32Z
publication:biosysengdiss
publication:agbiosyseng
publication:plantpath
publication:agronhortdiss
publication:unletdreports
publication:plantpathdiss
publication:ag_agron
<i>Panicum Mosaic Virus</i> Complex and Biofuels Switchgrass
Stewart, Catherine Louise
New switchgrass (Panicum virgatum L.) cultivars are being developed for use as a biofuel pyrolysis feedstock. Viral pathogens have been reported in switchgrass, but their importance in biofuel cultivars is not well known. In 2012 surveys of five switchgrass breeding nurseries in Nebraska, plants with mottling and stunting— symptoms associated with virus infection—had an incidence of symptomatic plants within fields as high as 59%. Leaves from 120 symptomatic plants were analyzed by ELISA for Panicum mosaic virus (PMV) and four other viruses known to infect switchgrass. Most samples (87%) were positive for PMV, and fewer than 8% for the remaining viruses. Among PMV-positive samples, 36% tested positive for the presence of PMV’s satellite virus (SPMV) by immunoblotting.
In 2013 fields were assessed for PMV- and PMV+SPMV-infection incidence and associated symptoms. PMV and SPMV were detected by ELISA and RT-PCR, respectively, in leaf samples from randomly selected plants. Symptom severity was assessed on these plants using a 1 to 5 scale (1 = no symptoms; 5 = plants stunted and >50% foliage with mottling). PMV incidence varied among fields and switchgrass populations within fields. Common among sampled populations was dual infection by PMV and SPMV. Few plants were infected with PMV alone and these exhibited symptoms at the 1-3 rating. There also were many PMV+SPMV-infected plants and these exhibited symptoms at the 1 to 5 rating.
To assess potential resistant switchgrass, four strains of switchgrass were grown in a growth chamber and rub-inoculated with PMV and PMV+SPMV. These were observed for 30 dpi and then collected. During the 30 dpi there was little symptom expression. Samples were weighed and tested for the presence of PMV or SPMV via RT-PCR. This study is on-going; however presently there is no evidence of resistance to either PMV or PMV+SPMV infection. However, the four switchgrass strains had less biomass accumulation if infected with either PMV or PMV+SPMV. There was no significant difference in biomass accumulation between PMV and PMV+SPMV infection.
Adviser: Gary Y. Yuen
2014-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/biosysengdiss/42
https://digitalcommons.unl.edu/context/biosysengdiss/article/1044/viewcontent/auto_convert.pdf
Department of Agricultural and Biological Systems Engineering: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Panicum mosaic virus
switchgrass
biofuels
pathogens
Agriculture
Plant Pathology
oai:digitalcommons.unl.edu:agronhortdiss-1078
2014-07-17T19:46:32Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Grazing Method Effects on Forage Production, Utilization, and Animal Performance on Nebraska Sandhills Meadow
Redden, Miles D
Mob grazing using ultrahigh stocking densities is promoted as a tool to increase the health and productivity of grasslands by increasing nutrient cycling and soil organic matter. Mob grazing can be defined as a strategy in which area available to grazing animals is restricted to achieve stocking densities of 200,000 kg/ha or greater. Objectives were to determine herbage production, utilization, and cattle weight gains among ultrahigh stocking density grazing and more conventional grazing methods on a Sandhills subirrigated meadow. Treatments included two replications of each of the following: four-pasture rotational grazing with two occupations per pasture in an 80-day grazing season (4-PR-2), four-pasture rotational grazing with one occupation per pasture in a 60-day grazing season (4-PR-1), and a mob grazing system with one occupation per pasture in a 60-day grazing season (MOB). In each of the four years (2010 – 2013), yearling beef cattle grazed the 4-PR-2 from mid-May through early August and the 4-PR-1 and MOB treatments from early June through early August. Stocking rates were equal among treatments within years but varied among years dependent on forage production. Stock densities were 225,000 kg/ha, 7000 kg/ha, and 5000 kg/ha for the MOB, 4-PR-1, and 4-PR-2 respectively. Herbage mass in grazing exclosures was used to estimate aboveground production in 2012 and 2013. Trampling and harvest efficiency were estimated every other week in the MOB and each time cattle changed pastures in the 4-PR-1 and 4-PR-2 during 2010, 2011, and 2013. Aboveground production did not differ among treatments. Average daily gains of MOB were low (0.2 kg/head/day) compared to 4-PR-2 gains (0.8 kg/head/day). Low gains on the MOB pastures likely were related to high levels of trampling and poor forage quality late in the grazing season.
Advisors: Walter H. Schacht and Jerry D. Volesky
2014-06-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/75
https://digitalcommons.unl.edu/context/agronhortdiss/article/1078/viewcontent/M._D._Redden_Thesis.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Mob grazing
grazing system
species composition
trampling
harvest efficiency
oai:digitalcommons.unl.edu:agronhortdiss-1079
2014-08-05T18:09:39Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Ammonia-Oxidizing Bacteria and Archaea Under Continuous Maize: The Influence of Tillage, N Input and Aggregation on Abundance and Community Composition
Segal, Lauren
Nitrification involves the oxidation of ammonium (NH4+) and is an important component of the overall N cycle. Nitrification occurs in two steps; first by oxidizing ammonium to nitrite, and then to nitrate. The first step is often the rate limiting step. Until recently ammonia-oxidizing bacteria (AOB) were thought to be the sole contributors to this process; however, the discovery of crenarchaeota, ammonia-oxidizing archaea (AOA), in marine environments has led to further study of their role in nitrification. Current literature supports the dominance of AOA over AOB in terrestrial ecosystems; however, little is known about what drives their abundance. To investigate the role of cropping system management on soil nitrifier abundance we sampled long-term continuous maize (25+ years) under two tillage treatments (tillage and no tillage) and five N fertilizer rates (0, 40, 80, 120, 160 kg ha-1 yr-1). Samples were collected three times during 2012; Pre-plant (5/1/12), after planting (5/14/12) and mid-season (7/6/12). Results show that AOA greatly outnumber AOB. The low AOB abundance may be attributed to niche differentiation between archaea and bacteria, as it was found that AOB were less resilient to N rate and tillage than AOA in monoculture maize. Little, if any, literature has examined soil structure as a possible niche. In previous studies, AOA have been shown to be more resilient to environmental conditions, than AOB. AOB abundance and community structure have been shown to be influenced by tillage, N-rate, and possibly plant growth; they also exhibited spatial heterogeneity. Given the different microenvironments in aggregate size fractions and AOA resistance to environmental conditions and habitat modification a second experiment examined the role of aggregate size fractions on AOB and AOA abundance. AOB were found to respond to soil depth and differed in concentration among aggregate size fractions although N rate still did not influence their abundance. AOA on the other hand was overall unresponsive to soil depth, N rate or aggregate size fraction; however, an N rate by depth interaction affected AOA abundance. Understanding the factors affecting AOB and AOA abundance are important to determine better soil management practices.
Advisor: Rhae Drijber
2014-07-28T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/76
https://digitalcommons.unl.edu/context/agronhortdiss/article/1079/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
AOA
AOB
Monoculture
qPCR
DGGE
FAME
Agronomy and Crop Sciences
Environmental Microbiology and Microbial Ecology
oai:digitalcommons.unl.edu:agronhortdiss-1080
2014-08-05T18:23:21Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Phenotypic Diversity in <i>Lysobacter enzymogenes</i> in Relations to Biological Control
Li, Ya
Strains of the bacterium Lysobacter enzymogenes have been isolated from various regions of the world and reported to have potential as biological control agents against plant pathogens. Previous research revealed many ecological traits and mechanisms important to biological control by L. enzymogenes. Much of the previous research, however, was conducted on individual strains with little direct comparison of different strains. In this study, L. enzymogenes strains isolated from different locations and source materials (soil, roots, leaves) were compared for biocontrol-related phenotypic traits in vitro, epiphytic and endophytic colonization of leaves, and biocontrol of Bipolaris leaf spot on tall fescue. The ability to colonize leaves endophytically by L. enzymogenes was found for the first time in this study. The trait was shown to be common to all of the strains tested, with only subtle differences among strains in endophytic colonization ability. Endophytic colonization occurred after spray application of strains to bean, cabbage, Swiss chard and tall fescue, but not green onion. All of the strains tested exhibited similar ability to produce yeast cell-degrading enzymes, β-1, 3-glucanase, and antifungal secondary metabolites. Finally, all strains tested for control of Bipolaris leaf spot inhibited development of the disease, with only slight differences in levels of disease suppression among the strains. It can be concluded from the collective results that the ability to colonize leaves endophytically, the expression biocontrol-related traits, and the potential to have biological control activity are traits that are common to L. enzymogenes strains in general regardless of their origin.
Advisor: Gary Y. Yuen
2014-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/77
https://digitalcommons.unl.edu/context/agronhortdiss/article/1080/viewcontent/Ya_Li_2014_Thesis_Phenotypic_diversity_L_enzymogenes.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Lysobacter enzymogenes
biological control
phenotypic traits
phyllosphere colonization
endophyte
comparison
Plant Pathology
oai:digitalcommons.unl.edu:agronhortdiss-1081
2014-08-06T16:48:34Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Functional Genomics of Maize Endosperm Maturation and Protein Quality
Yuan, Lingling
Maize is one of the most important cereal crops and widely cultivated throughout the world. The study on maize kernel development including protein quality improvement is essential for removing dietary protein deficiency because of the lack of essential amino acids, especially lysine and tryptophan, in maize kernel. Quality Protein Maize (QPM) is a hard kernel variant of the high-lysine mutant, opaque-2. We created opaque QPM variants to identify opaque-2 modifier genes and to investigate deletion mutagenesis combined with Illumina sequencing as a maize functional genomics tool. A K0326Y-QPM deletion mutant, line 107, was null for the 27- and 50-kD γ-zeins and abolished vitreous endosperm formation. Characterization of line 107 identified 27-kD γ-zein as an opaque-2 modifier gene within the largest QPM QTL, and may suggest the 50-kD γ-zein also contributes to this QTL. It further demonstrates that genome-wide deletions in non-reference maize lines can be identified through a combination of assembly of Illumina reads against the B73 genome and integration of RNA-seq data. Characterization of a low α-zein mutant, line 198, mapped its mutation on chromosome 3.02 and I describe our efforts towards its molecular identification.
Besides the K0326Y-QPM mutagenesis project, I made a significant contribution to the study of zein function and their inverse relationship to kernel protein quality by using RNA interference. I addressed the extent of functional non-redundancy within the γ- and α-zein subclasses. My involvement in this work was in-depth analysis of transcript and protein levels in endosperms of these lines.
I was also involved in the characterization of a sorghum high digestibility high lysine opaque mutant hdhl. We found that the mutant results from the missense mutation results in the 21st conserved amino acid alanine (Ala) in the signal peptide being replaced with threonine (Thr), which renders the signal peptide resistant to processing, indirectly reducing the levels of lysine-poor kafirins and thereby increasing lysine-rich proteins and protein digestibility in the seeds.
Advisor: David R Holding
2014-07-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/78
https://digitalcommons.unl.edu/context/agronhortdiss/article/1081/viewcontent/PhD_Thesis_Lingling_Yuan_7_29_2014.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
maize
genomics
endosperm
protein
Agriculture
Agronomy and Crop Sciences
Genetics and Genomics
Molecular Genetics
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1082
2014-08-06T20:09:22Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
EFFECTS OF CULTURE MEDIA AND PLANT GROWTH REGULATORS ON MICROPROPAGATION OF WILLOW (<i>Salix matsudana</i> ‘Golden Spiral’) AND HAZELNUT (<i>Corylus colurna</i> ‘Te Terra Red)
Shi, Dongxue
The branches and leaves of Salix matsudana ‘Golden Spiral’ , willow, grow in a twisted manner, which makes it an important bonsai plant. Its mature stems have potential for the woody cut floral industry. Corylus colurna ‘ Te Terra Red’, hazelnut, distinguished by red or purple leaves in the spring, has potential ornamental value in the horticulture industry for landscape use. Micropropagation of these two plants could provide more and healthier plantlets for rapid commercial scale-up by the nursery industry. Nas and Read Medium (NRM) is a newer medium developed specifically for hazelnut species by Nas and Read based on the composition of the seed. In this study, experiments were conducted to test whether NRM (with added plant growth regulators) is superior to other media such as Murashige and Skoog Medium (MS), Woody Plant Medium (WPM) and Driver-Kuniyuki Walnut medium (DKW) for shoot and root production of Salix and Corylus. The results showed that Salix explants grown in NRM with BA at 2.0mg/L and IBA at 0.05 mg/L produced a greater number of new shoots and longer stems. Explants grown in NRM with IBA at 0.05 mg/L produced more roots, which is necessary before transplanting to the soil. In addition, these plantlets exhibited deeper green color and acclimatized successfully into potential transplants. The hazelnut explants had a very high contamination rate and grew slowly on the various media. By improving disinfestation methods and by adding antibiotics in forcing solution and media, the contamination rate and browning rate can be decreased greatly.
Advisor: Paul E. Read
2014-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/79
https://digitalcommons.unl.edu/context/agronhortdiss/article/1082/viewcontent/THESIS_WITH_COVER_PAGE.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Micropropagation
Salix
Corylus
media
plant growth regulators
Agriculture
Horticulture
Other Plant Sciences
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1083
2014-08-08T19:29:50Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
AN EVALUATION OF WATERMELON (<i>Citrullus</i> spp.) GERMPLASM FOR ADDITIONAL SOURCES OF RESISTANCE TO THE TWOSPOTTED SPIDER MITE (<i>Tetranychus urticae</i> Koch).
Cantu, Hector, Jr.
Fourteen U.S plant introduction (PI) accessions of C. lanatus var. lanatus (4), C. lanatus var. citroides (5) C. colocynthis (5) and a known susceptible commercial cultivar ‘Sugar Baby’ were evaluated for resistance to the twospotted spider mite, Tetranychus urticae Koch, in a limited free-choice and free-choice bioassay under laboratory conditions. The limited free choice bioassay, involved nine Petri dish cages that held five randomly assigned leaves individually inoculated with two adult females and one adult male. Eggs, larva, and adults were counted over a nine day period. The free choice bioassay involved the even distribution of three mite infested pinto bean pots among the 15 accessions per tier under evaluation. Four tiers (syn. replications) consisting of fifteen randomized accessions were evaluated over a three week period. In both bioassays the two-spotted spider mite strongly preferred feeding and completing its life cycle on C. lanatus var. lanatus and C. lanatus var. citroides compared to C. colocynthis. Among the C. colocynthis accessions evaluated, PI 388770, PI 525080, and PI 537300 had consistently lower injury ratings and total mite populations (eggs, adults, larva) when compared to the other PIs and the susceptible cultivar ‘Sugar Baby’. Preliminary research indicated that feeding tolerance was also found to be significantly different by changing the way we did mite counts (i.e., uncut mite counts; excised leaf counts), but a more thorough study is needed. Ultimately, this study has identified two more possible sources of two-spotted spider mite resistance in PI 525080, and PI 537300 and adds further support for the already identified resistant PI 388770.
Advisors: Tom Hoegemeyer and P. Stephen Baenziger
2014-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/80
https://digitalcommons.unl.edu/context/agronhortdiss/article/1083/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agricultural Science
Agronomy and Crop Sciences
Botany
Entomology
Horticulture
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1084
2014-09-17T16:55:26Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Selection and Genetic Drift in North American Maize
Lamkey, Collin
Characterizing the impact of selection and genetic drift in the formation of heterotic groups and patterns in maize can reveal important insights into the mechanism underlying adaptation, and the relative importance of each force in defining population structure. The objectives were to characterize the role selection for hybrid performance had in defining population structure in both a reciprocal full-sib selection (RFS) program and a large collection of historically important inbred lines.
The Illumina GoldenGate Assay was used to genotype the University of Nebraska-Lincoln Replicated Recurrent Selection (UNL-RpRS) program. Eight cycles of S1-progeny and RFS selection were conducted for an index approximating grain yield. The distance between S1-progeny programs was compared to the distance between RFS selection programs. No evidence was found to suggest a significant genome-wide impact of selection for hybrid performance. This result suggests that, genome-wide, selection was not a strong force in diverging populations.
To further investigate the roles of selection and genetic drift a second dataset was generated with genotype-by-sequencing data accompanied by increased sample size for each population in the UNL-RpRS program. A dense physical map was generated, which allowed genomic localization of selection signatures associated with directional selection and also selection for hybrid performance. The RFS and S1-progeny selection programs left similar signatures of selection across the genome. A scan for directional selection identified similar regions under selection across replicate populations, which suggests that adaptation is occurring from standing genetic variation.
A large collection of inbred lines was collected and grouped into four eras, which represented the double-cross, three-way cross to single-cross transition, single-cross, and advanced single-cross eras of maize breeding, respectively. A small number of inbred lines were found to contribute to the parentage of the next era. The inbred lines identified here were also major contributors in other studies as well. Scanning the genome for localized selection signatures revealed genes putatively associated with cold tolerance and resistance to fungal and bacterial pathogens, which is consistent with the notion that selection for increased yield has selected hybrids with increased tolerance to biotic and abiotic stresses.
Advisor: Aaron J. Lorenz
2014-09-09T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/81
https://digitalcommons.unl.edu/context/agronhortdiss/article/1084/viewcontent/CollinLamkey_Dissertation_v992014_v1.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
selection
genetic drift
UNL-RpRS
RFS
S1
Agronomy and Crop Sciences
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1085
2014-11-11T21:37:42Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
THE EFFECT OF INBREEDING DIALLEL CROSSES OF INBRED LINES OF CORN SELECTED FOR HIGH AND LOW
COMBINING ABILITY
Rumbaugh, Melvin Dale
The present day hybrid seed corn industry is based upon the development and utilization of inbred lines in hybrid combination. Current breeding procedures are largely predicated on the assumption that the actions of complementary, dominant or partially dominant favorable genes are responsible for the heterosis observed in the hybrids produced. If heterosis were due in considerable part to nonallelic interactions or to overdominance, the present breeding procedures might be expected to yield superior hybrids but would not be highly efficient.
Since the proposal of complementary growth factors as a genetic explanation of heterosis and the alternative proposal of physiological stimulation due to heterozygosity per se, a considerable body of information bearing on the problem has been accumulated. The results obtained and the interpretation of these results do not permit completely satisfactory conclusions as to the relative importance of the various types of gene action believed to be present. The present research problem is an attempt to gain further evidence on this point by means of a critical evaluation of the relationship between the inbreeding depression of a set of diallel crosses and the combining ability level of the inbred corn lines used as parents.
1958-01-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/82
https://digitalcommons.unl.edu/context/agronhortdiss/article/1085/viewcontent/Rumbaugh_diss_1958_Agronomy.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agriculture
Agronomy and Crop Sciences
Plant Breeding and Genetics
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1086
2014-12-01T18:14:06Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
CONTROL OF HERBICIDE-RESISTANT VOLUNTEER CORN IN HERBICIDE-RESISTANT SOYBEAN
Chahal, Parminder
Volunteer corn is a problem weed in soybean fields because it reduces yield and seed quality, and potentially harbors insects, pests, and diseases. Several pre-packaged herbicides have been registered in soybean in recent years, but response of volunteer corn to these herbicides has not yet been documented. Therefore, the first objective of this study was to evaluate the response of glufosinate-, glyphosate-, and imidazolinone-resistant volunteer corn to 20 pre-emergence (PRE) and 17 post-emergence (POST) soybean herbicides. The results indicated that PRE soybean herbicides partially controlled (< 80%) volunteer corn except clomazone, while acetyl CoA carboxylase (ACCase) inhibiting herbicides provided ≥ 85% control. Germination and emergence are critical stages in weed seed establishment and persistence. Scientific literature is not available about the factors affecting germination and emergence of volunteer corn. The second objective was to determine the effects of different environmental and agronomic factors on the germination and emergence of glyphosate-resistant hybrid and volunteer corn. The results indicated that response of hybrid and volunteer corn to majority of the variables tested was similar, suggesting that volunteer corn can germinate and emerge in a wide range of climatic conditions. Majority of growers control volunteer corn when it is visible above the soybean canopy, but this can results in early season competition with soybean. The third objective was to evaluate the impact of different densities of glyphosate-resistant volunteer corn at different control timings, and late season volunteer corn emergence on soybean yields. Late season volunteer corn emergence had no significant effect on soybean yield. Yield did not decrease with all volunteer corn densities, except with the highest density (10,000 plants and 500 clumps ha-1) at all control timings. Soybean growers are looking for alternative herbicides, such as glufosinate, for management of glyphosate-resistant weeds, including volunteer corn. The fourth objective was to evaluate different herbicide programs for control of glyphosate-resistant volunteer corn in glufosinate-resistant soybean. The results suggested that glufosinate applied at different rates in a single or sequential application provided ≥ 85% control of volunteer corn along with other weeds. These results will provide useful information to soybean growers for management of volunteer corn.
Adviser: Amit J. Jhala
2014-11-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/83
https://digitalcommons.unl.edu/context/agronhortdiss/article/1086/viewcontent/Chahal_s_MS_Thesis1.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
glufosinate
glyphosate
imidazolinone
Agriculture
Agronomy and Crop Sciences
Weed Science
oai:digitalcommons.unl.edu:agronhortdiss-1087
2015-08-03T19:44:03Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Litter Decomposition and Root Production in Response to Grazing on Sandhills Subirrigated Meadow
Beckman, Ben W.
Stocking density can be manipulated by management factors including herd size, pasture size, and grazing period length. Ultrahigh stocking density (mob grazing) is commonly characterized at 200,000 kg animal live weight ha-1 or higher with multiple movements of livestock per day. Practitioners claim increased plant production, soil development, and nutrient cycling rates because of high trampling percentages resulting from ultrahigh socking densities. This study was conducted on subirrigated meadow in the Nebraska Sandhills in 2012 and 2013 to determine grazing method effect on annual root production and litter decomposition. Stocking rates were held constant while stocking densities varied by treatment. Treatments included two replications of mob grazing (202,000 kg ha-1), 4-pasture rotation grazing (4-PR-1) (6700 kg ha-1), continuous grazing (5000 kg ha-1), and an ungrazed control. Cattle grazed for 60 days from early June to early August. Each May, 12 soil cores (5 cm diameter x 15 cm depth) per treatment replication were taken and roots removed. Root-free soil was placed in mesh cylinders of the same dimensions as the cores and inserted into the cores in the field. The mesh cylinders were excavated in November and roots separated from soil, dried, and weighed. Mob grazing did not increase root production. The control contained 60% more annual root biomass (P < 0.05) than grazing. In June and July, wire mesh bags containing 1.5 g of stem and leaf material of quackgrass (Elymus repens L.) were placed at eight locations in the mob, 4-PR-1, and control. Bags were placed on the soil surface either in grazing exclosures measuring effects one year after grazing or in a mob-grazed paddock immediately following grazing. Four samples were retrieved per replication after 1, 5, 9, 21, and 46 weeks. Samples were dried and weighed to determine biomass disappearance and decomposition rate. The dried samples were analyzed for nitrogen (N), carbon (C), and Neutral Detergent Fiber (NDF) contents. Mob grazing did not affect decomposition rate, N or C levels, or fiber. Month of placement differed in all variables with June placements decomposing faster, had lower C, higher N, and lower fiber.
Advisors: Walter H. Schacht and Jerry D. Volesky
2014-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/89
https://digitalcommons.unl.edu/context/agronhortdiss/article/1087/viewcontent/Beckman_Thesis_Final.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
grazing systems
ultrahigh stocking density
litter decomposition
annual root production
Agriculture
Other Animal Sciences
Other Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1088
2014-12-05T18:21:04Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Carbohydrate Metabolism and the Trehalose Biosynthetic Pathway in Maize Kernels Grown <i>In Vitro</i> under Sucrose Starvation Stress
Bledsoe, Samuel W
Drought is an increasing issue that many farmers encounter especially in hot arid climates with little rainfall. High temperatures and inadequate rainfall at certain stages in crop development can have disastrous consequences to yield. In maize, drought occurring near or during the flowering stage often causes significant kernel abortion that greatly impacts potential yield. The trehalose biosynthetic pathway has recently been found to be important in plant metabolism in response to stress in higher order plants. Trehalose is currently known throughout the plant and animal kingdoms as an osmoprotectant, high energy fuel source, structural component, and involved in pathogen response. New insight on the role of the trehalose pathway focuses on the sugar phosphate intermediate trehalose-6-phosphate (Tre6P) and its regulatory role on the Sucrose non-fermenting Related Kinase 1 (SnRK1). SnRK1 has been shown to be a central regulator of numerous catabolic and anabolic events critical to plant metabolism. Slight changes in trace Tre6P levels within the plant often cause dramatic phenotypes suggesting that Tre6P is acting as a metabolic switch in response to carbon availability. Understanding the role of the trehalose and SnRK1 pathways in higher plant species such as maize will provide a better understanding of carbon partitioning in plants especially as it pertains to kernel abortion and potentially increasing yields. This study first explores the practicality of in vitro kernel culture as a means to evaluate sink strength in the context of regulation by Tre6P and the SnRK1 pathway on maize inbred B73, a Nested Association Mapping (NAM) population parent line, and the model organism for this study. Sink strength is then characterized for 14 additional NAM inbred parent lines as well as a more detailed analysis of Tre6P and SnRK1 involvement for selected inbred lines Oh43 and M37W. The findings of this study greatly support the involvement of the SnRK1 pathway in response to sucrose starvation stress and its regulation by Tre6P.
Advisor: Mark Lagrimini
2014-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/84
https://digitalcommons.unl.edu/context/agronhortdiss/article/1088/viewcontent/Thesis_12_3_14.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
trehalose
drought
metabolism
maize
kernels
sucrose starvation
in vitro
Agronomy and Crop Sciences
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1089
2015-04-13T19:38:32Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Biology and Control of Glyphosate-Resistant Giant Ragweed.
Kaur, Simranpreet
Giant ragweed is a troublesome, early emerging, summer annual weed found throughout the eastern and midwestern corn and soybean growing regions of the United States. Since the emergence of giant ragweed varies at different locations, our first objective was to determine the emergence pattern of giant ragweed in Nebraska and how spring tillage influences emergence. Results of a two-year study suggested that giant ragweed emerged from late March until mid-June, with the majority of emergence ceasing by early May. Spring tillage could be used as an alternative method for managing glyphosate resistant giant ragweed.
Water stress can affect the growth and development of both crop plants and weeds. Thus, in our second objective, we hypothesized that drought conditions can result in a water deficit that can hinder giant ragweed growth and reproduction. Results suggested that the degree of water stress had more effect on plant growth and fecundity compared to the duration of water stress. Plants watered at a 10-day interval with 100% field capacity were still able to produce seeds, whereas only a few plants survived at 12.5% soil moisture content when irrigated at a 2-day interval.
Early emergence and a rapid growth rate make giant ragweed a competitive weed early in the season and reduce crop yields; therefore, in our third objective, we determined the early spring control of giant ragweed using a preplant herbicide. Several herbicide programs were investigated with preplant followed by pre-emergence (PRE) and post-emergence (POST) herbicides for controlling glyphosate-resistant giant ragweed
in glufosinate-resistant soybean. Results suggested that herbicide programs containing 2,4-D in preplant followed by an in-crop application of glufosinate provided 99% control of glyphosate-resistant giant ragweed and increased soybean yields.
Finally, since fall and early spring application of herbicides may influence giant ragweed emergence, our fourth objective was to determine the effect of fall and/or early spring application of a prepackaged mixture of iodosulfuron and thiencarbazone-methyl applied alone or tank-mixed with 2,4-D, dicamba, or metribuzin on glyphosate-resistant giant ragweed in no-till corn. Results suggested that the premix of iodosulfuron and thiencarbazone-methyl tank-mixed with 2,4-D, dicamba, or metribuzin followed by PRE and POST herbicide applications provided > 95% control of glyphosate-resistant giant ragweed in no-till corn.
Advisor: Amit J. Jhala
2015-03-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/85
https://digitalcommons.unl.edu/context/agronhortdiss/article/1089/viewcontent/Thesis_SimranpreetKaur3_pdf.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Giant Ragweed
summer annual weeds
weed control
growing degree days
herbicide resistance
Agriculture
Agronomy and Crop Sciences
Life Sciences
Plant Sciences
Weed Science
oai:digitalcommons.unl.edu:agronhortdiss-1090
2015-04-27T14:08:12Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Maize Yield and Components as Influenced by Environment and Agronomic Management
Milander, Jeremy J.
Yield component analysis research on dent maize and waxy maize (Zea mays L.) as related to crop management is limited in Europe and the United States. Two research studies were conducted in 2012 and 2013 at Mead and North Platte, NE and Zagreb, Croatia with the objective to determine the influence of environment, water regime, hybrid, and plant population on maize yield and yield components. Grain yield, ears m-2, kernels ear-1, kernels row-1, rows ear-1, ear length and circumference, and kernel weight were measured. Environment and water regime altered maize yield components depending upon the timing and degree of stress present. Early-season stress reduced the number of ears m-2, late-season stress reduced kernel weight, and mid-season stress reduced the number of kernels m-2. The Mead 2013 environment produced the highest grain yield of 11.7 Mg ha-1, while the lowest average yield was 7.0 Mg ha-1 in the North Platte 2012 environment. Irrigation increased grain yield by 3.1 to 3.3 Mg ha-1 at Mead and 8.1-12.7 Mg ha-1 at North Platte. Hybrid altered yield and yield components, with the most differences in this study related to maturity classifications. Plant population had no effect on grain yield across populations which was 10.7 Mg ha-1. Ears m-2 increased from 6.6 to 9.4 with increasing plant population while the number of rows ear-1 decreased from 16.2 to 15.0, and kernels ear-1 from 546 to 410. Kernels ear-1 was the yield component most highly correlated with yield (R =0.47 to 0.78) in the plant population study and North Platte dryland environment for the waxy study, while kernel weight was the most highly correlated (R = 0.67) in the Mead and North Platte irrigated environments in the waxy study. Waxy maize was found to have a similar yield potential and interactions among yield components to dent maize. Results indicated that environment, plant population, hybrid and water regime affect maize grain yield and its components and that stress timing correlates with developing yield components.
Advisor: Steve Mason
2015-02-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/86
https://digitalcommons.unl.edu/context/agronhortdiss/article/1090/viewcontent/Milander_Thesis_4_21_2015.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Corn
Yield Components
Grain Yield
Path Analysis
Plant Population
Water Regime
Environment
Hybrid
Croatia
Nebraska
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1091
2015-05-01T17:36:13Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
IMPACT OF ARBUSCULAR MYCORRHIZAL FUNGI ON THE PHYSIOLOGY OF MAIZE GENOTYPES UNDER VARIABLE NITROGEN AND PHOSPHORUS LEVELS
Crespo, Roberto
It is important to increase our understanding of AM fungal and maize genotype interactions, the impact of N and P fertilization and water condition on the symbiosis, and on the physiology and nutritional status of maize plants. In two greenhouse experiments AM inoculated plants exhibited root colonization values around 70% which was confirmed by the presence of the AM lipid biomarker (C16:1cis11). Nitrogen fertilization increased AM root colonization, but only compared to unfertilized plants. Root colonization and biomarker concentration in root and soil were similar among inoculated maize genotypes across conventional and drought tolerant hybrids. Mycorrhizal inoculation had a positive impact on maize plant P uptake, but neither increased N uptake nor chlorophyll content in leaves. Nitrogen fertilization increased P concentration in plant tissue under AM inoculation, but decreased P concentration under non-inoculated conditions. There were positive plant biomass and chlorophyll responses as N fertilization increased, but not for P fertilization. Except for increased P uptake, results from both greenhouse studies are inconclusive about why most of the parameters evaluated were unresponsive or negatively affected by AM inoculation. In a field experiment, indigenous AM fungi effectively colonized maize roots to the same magnitude regardless of maize genotype and soil water condition. Increased soil extramatrical AM biomass, suggesting greater C allocation from plant to AM fungus, was observed under water-limited conditions and also among maize genotypes. In addition, while water limitation caused a shift in the overall soil microbial community, maize hybrids influenced specific microbial groups. Bacterial and actinomycete markers, and also total microbial biomass significantly increased under water stress. Interactions among AM fungi, plants and nutrients appear to be complex making plant responses to AM fungi difficult to predict and explain. Further studies on the mechanisms involved are needed to gain further insight into the complex relationships among AM fungi, maize and soil fertility management to maximize benefit from the AM fungi/plant symbiosis.
Adviser: Rhae Drijber
2015-04-27T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/87
https://digitalcommons.unl.edu/context/agronhortdiss/article/1091/viewcontent/Crespo_PhD_Dissertation_FINAL_April26.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Arbuscular mycorrhiza
maize genotypes
nitrogen and phosphorus fertilization
soil microbial community
maize physiology
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1092
2023-02-17T21:25:16Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Biochemical and Proteomic Profiling of Maize Endosperm Texture and Protein Quality
Morton, Kyla J
The research described herein, focuses on the biochemical and proteomic analysis of the maize endosperm and what influences kernel texture. Quality Protein Maize (QPM) is a hard endosperm version of the high-lysine opaque2 (o2) mutant but the genes involved in modifying the soft o2 endosperm are unknown. Pyrophosphate (PPi)-dependent fructose 6-phosphate 1-phosphotransferase (PFP) catalyzes the ATP-independent conversion of fructose 6-phosphate to fructose 1, 6-bisphosphate in glycolysis. We found a large increase in transcript and protein levels of the alpha regulatory subunit of PFP (PFPα) in QPM endosperm. In vitro enzyme assays show a significant increase in forward PFP activity in developing endosperm extracts of QPM relative to wild type and o2. Furthermore, the O2 regulated pyruvate Pi dikinase (PPDK) gene is reduced in expression and activity in o2. Normal vitreous endosperm in QPM may occur due to modulation of glycolytic flux attributable to increased enzyme activity at two regulatory enzymes of glycolysis, PFP and PPDK.
Opaque endosperm is most often attributed to either quantitative or qualitative changes in zein accumulation. However, some opaque endosperm mutants have normal zein accumulation. In order to identify factors involved in vitreous endosperm formation or its disruption (opacity) we conducted shotgun proteomic analysis of the nearly isogenic lines of six opaque endosperm mutant non-zein fractions. Our proteomic data indicates that there is not one specific cause of endosperm opacity apart from the non-ubiquitous reduction of zeins. We suggest that mis-regulation of zein deposition on the ER membrane or improper trafficking either upon loading or unloading from the ER membrane causes cellular stress which could invoke opacity.
A mutagenized B73 population (MB73) was also created as an additional method to identify genomic regions and ultimately, genes involved in vitreous and/or opaque endosperm texture as well as create variants with proteomes rebalanced towards improved endosperm protein quality.
Advisor: David R. Holding
2015-07-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/88
https://digitalcommons.unl.edu/context/agronhortdiss/article/1092/viewcontent/Morton_2015_DISS.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Maize
Endosperm
Opaque
Vitreous
QPM
Quality Protein Maize
Proteomics
Agricultural Science
Agronomy and Crop Sciences
Plant Biology
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1093
2015-08-07T16:41:29Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Rust Diseases on Switchgrass (<i>Panicum virgatum</i>)
Ma, Ying
Switchgrass (Panicum virgatum) is a perennial C4 grass native to the central prairies of North America. Recent development of switchgrass as a sustainable biofuel feedstock has raised interest in diseases that could impact switchgrass, especially when grown under monoculture conditions. Among the known diseases of switchgrass, rust diseases are the most widespread and could potentially impact yield and biomass quality of new switchgrass cultivars. Two species of rust fungi, Uromyces graminicola and Puccinia emaculata, are known to infect switchgrass, with P. emaculata being the primary or sole rust pathogen on switchgrass in southern US states. The relative importance of each of the two species in the North Central region, however, was unknown. In this study, the rust fungi on switchgrass samples collected from various locations in Nebraska, Illinois, Indiana, Missouri and Wisconsin were identified on the basis of teliospore morphology and DNA sequence analysis. Both U. graminicola and P. emaculata were found in samples from Nebraska and Wisconsin, whereas P. emaculata only was found in samples from the other states. Among 22 switchgrass strains evaluated in a Nebraska varietal experiment, lowland types were found to be more resistant to rust than upland types. Most upland switchgrass strains were infected by both rust species, while most lowland switchgrasses were infected by P. emaculata only. The results indicate that development of new biofuel switchgrass cultivars, particularly those intended for the northern plains, must include improved resistance against both rust species. As a new tool to facilitate future switchgrass research and resistance breeding efforts, a diagnostic polymerase chain reaction (PCR) system was developed whereby the two rust species can be distinguished in individual infection lesions and in infected leaves. The system utilized three sets of primers, one set (UgF and UgR) designed in this study specifically for U. graminicola on the basis of its internal transcribed spacer sequence, and the other two being previously-reported primers diagnostic for P. emaculata and for all rust fungi.
Advisor: Gary Y. Yuen
2015-08-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/90
https://digitalcommons.unl.edu/context/agronhortdiss/article/1093/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Plant Pathology
oai:digitalcommons.unl.edu:agronhortdiss-1094
2015-08-10T14:03:58Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
NITROGEN AND WATER EFFECTS ON CANOPY SENSOR MEASUREMENTS FOR SITE-SPECIFIC MANAGEMENT OF CROPS
Ward, Nicholas C
Water and nitrogen (N) are undoubtedly the two largest agricultural inputs globally. Coupled with advances in site-specific management technology their integration into production agriculture will allow for the most efficient use these crop input resources. Active canopy sensors offer the ability to measure biophysical plant traits rapidly and make assessments about plant status. Specifically, optical sensor measurements of light reflectance assess plant N status allowing for in-season and on-the-go N recommendations and applications; while infrared thermometers (IRT) measurement of canopy temperature can be used a tool for irrigation management. To evaluate how these technologies work among different plant stress environments a series of experiments were formulated. The first experiment compared reference strategies for normalizing reflectance data across multiple vegetation indices (VI). We found the virtual reference concept helped reduce variation of the calculated reference and placed sufficiency index values in a range that corresponded to plant N status. Additionally, VI varied in their ability to show significant responses to applied N fertilizer. In the second experiment, we sought to understand the influence of VI on how an in-season N application algorithm performs as well as the confounding effects of irrigation might have. We found N application rates would change based on algorithm and VI. Also, N rate can be affected by apparent water stress. In this case, reduced reflectance in the NIR spectrum reduced leaf area from leaf rolling. The final objective was to quantify the effect of N fertility on plant canopy temperature and determine if functions of canopy temperature could be useful for detecting apparent N stress. We concluded that plant canopy temperature can be affected by N stresses and that canopy temperature and canopy/air temperature difference provided equal sensitivity to plant stress. Therefore, these technologies will be vital to help conserve resources and maximize efficiency in production agriculture.
Advisor: Richard Ferguson
2015-07-31T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/91
https://digitalcommons.unl.edu/context/agronhortdiss/article/1094/viewcontent/Dissertation_WARD_August2015.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
corn
irrigation
canopy reflectance
canopy temperature
nitrogen
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1095
2015-08-10T14:13:33Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Discovery and Delimitation: Criconematid Nematodes of North American Grasslands
Olson, Magdalena Jean
Approximately 200 years ago, North American landscapes were dominated by vast expanses of grassland. The Great Plains, an ecologically complex and diverse ecoregion, extended from Canada to the Gulf of Mexico, and from the Rocky Mountains to the border of the eastern hardwood forest in Indiana. Now the original tallgrass prairie exists in small widely dispersed remnant patches surrounded by agroecosystems. This study is an effort to characterize soil nematode diversity and population structure within those remnant patches. The plant parasitic nematode family Criconematidae serves as our indicator for nematode diversity, due to its global distribution, high abundance in natural areas, broad host range, limited dispersal capabilities, and the availability of a highly resolved COI gene tree. Thirty-one grassland sites representing 13 ecoregions were sampled by extracting soil cores within a 40 x 40m grid. Criconematid nematodes were screened and isolated using soil sieves and centrifugation. Nematodes were individually photographed, measured and amplified with a primer set that, after removing primers, results in 721 nucleotides of the COI mitochondrial gene. Diversity was studied at different levels, from morphospecies to haplotype lineages and haplotype diversity within lineages. Grassland lineages were investigated using phylogenetic methods and species delimitation methods. One hundred and ninety five nematodes conforming morphologically to Mesocriconema curvatum of broad geographic distribution, spanning the central tallgrass ecoregion were analyzed as cryptic species. Where morphological analysis would indicate the presence of a widespread, cosmopolitan species, species delimitation analyses, including the construction of phylogenetic trees, Automatic Barcode Gap Discovery, the Species Delimitation Plugin implemented through Geneious R8, and statistical parsimony networks indicate approximately ten well-supported, genetically distinct clades. Two of these clades contain over seventy specimens each and are characterized by distinct intra-specific population structures, suggesting unique evolutionary forces responsible for their speciation and diversification. While these two clades, or cryptic species possess independent population structures, they are both associated with sister clades of southern sites, indicative of ancestral origins in states such as Arkansas, Oklahoma, and Texas.
Advisor: Thomas O. Powers
2015-07-31T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/92
https://digitalcommons.unl.edu/context/agronhortdiss/article/1095/viewcontent/M._Olson_MS_Thesis_Jul_2015_PDF.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Grassands
diversity
nematode
criconematid
DNA barcoding
COI
cryptic species
species delimitation
biogeography
molecular taxonomy
integrative taxonomy
Biodiversity
Other Ecology and Evolutionary Biology
Terrestrial and Aquatic Ecology
oai:digitalcommons.unl.edu:agronhortdiss-1096
2015-12-04T15:52:34Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Understanding the biology, inheritance and mechanism of resistance of 2,4-D resistant waterhemp (<i>Amaranthus tuberculatus</i>) - Research Proposal
Crespo, Roberto
Waterhemp is a very well adapted summer annual weed to the U.S. Corn Belt region. Auxinic herbicides such as 2,4-D constitute effective and widely used herbicides to control waterhemp and other broadleaf species in cereal crops and turf grasses. Recently, Bernards et al. (2012) have reported a Nebraska waterhemp biotype has evolved resistant to 2,4-D. This finding represents the sixth mode-of action herbicide group to which waterhemp has evolved resistance to. Several attributes may have contributed to make waterhemp a very successful weed and prone to evolve to herbicide resistant: a high genetic variability, aggressive growth habits and high fecundity. The hypothetical scenario of a waterhemp population resistant to several herbicide mode of action constitutes a challenge on weed management, since a traditional herbicide use program could result in unmanageable situation. Several studies that have contributed to the basic understanding for auxinic herbicide resistance are presented. The proposed objectives of this study are: 1) to evaluate the response of the 2,4-D resistant waterhemp population to several other herbicides mode of action,, 2) to assess the type of inheritance pattern of 2,4-D resistance in waterhemp, and 3) to determine if the mechanism of 2,4D resistance in waterhemp is due to differential absorption, translocation, or metabolism of 2,4-D.
2012-03-19T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/93
https://digitalcommons.unl.edu/context/agronhortdiss/article/1096/viewcontent/Crespo_PhD_Proposal_DIGITALCOMMONS.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Waterhemp
Amaranthus tuberculatus
2
4-D
herbicide resistant weeds
multiple resistance
Agriculture
Plant Sciences
Weed Science
oai:digitalcommons.unl.edu:agronhortdiss-1097
2015-12-04T15:54:09Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Assessing Multiple-Herbicide Resistance in a 2,4-D Resistant Waterhemp (Amaranthus tuberculatus) Biotype from Nebraska – Student Research
Crespo, Roberto
A waterhemp biotype was recently reported resistant to 2,4-D in Nebraska. In addition to the repeated use of 2,4-D, atrazine and imazathapyr were reported to be frequently used to control broadleaf weeds. Greenhouse experiments were conducted to confirm 2,4-D resistance and test for resistance to growth regulator herbicides and other herbicide modes-of-action (MoA). A single dose-response experiment showed reduced sensitivity in all three waterhemp biotypes to atrazine, imazethapyr and lactofen; therefore, they were generally considered resistant to those three herbicide MoA. None of the biotypes contained the Ser264 target-site mutation. Since the ametryn dose-response experiment resulted in all susceptible biotypes, atrazine resistance is suspected to be metabolism based. Trp574Leu mutation conferring broad cross-resistance to ALS-inhibiting herbicides including imidazolinones and sulfonylureas was identified in the two 2,4-D susceptible waterhemp biotypes. Trp574Leu mutation was not found in the 2,4-D resistant biotype, but Ser653 mutation conferring resistance to imidazolinones was identified. However, dose-response experiments showed reduced sensitivity of the 2,4-D resistant biotype to chlorimuron-ethyl. Despite the 50% survival rate or higher of plants treated with lactofen, results from sequencing the PPX2L gene conferring resistance to PPO-inhibitor herbicides were not quite clear. The present manuscript confirms that the 2,4-D resistant biotype found in Nebraska is also resistant to herbicides belonging to PSII- and ALS-inhibitors. Additionally, the 2,4-D resistant biotype is resistant and has reduced susceptibility to some other growth regulator herbicides.
2015-10-10T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/94
https://digitalcommons.unl.edu/context/agronhortdiss/article/1097/viewcontent/Crespo_Multiple_Resistance__DIGITALCOMMONS.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Dose-response
injury
herbicide resistance
2
4-D-resistant waterhemp
cross-resistance
Agriculture
Agronomy and Crop Sciences
Plant Sciences
Weed Science
oai:digitalcommons.unl.edu:agronhortdiss-1098
2015-12-11T15:53:41Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Improving Establishment of Seeded Buffalograss
Li, Luqi
Buffalograss [Buchloë dactyloides (Nutt.) Engelm.] is a warm-season grass native to the North American Great Plains. Buffalograss is drought resistant, heat resistant and cold tolerant, and thus is well-adapted to many uses in areas that require low maintenance or erosion control. Since buffalograss is slow-growing, one challenge of establishing seeded buffalograss is to maximize seedling maturation and establishment before winter. We evaluated dormant seeding buffalograss in late fall and winter, when germination is not expected until soils warm in spring. We successfully dormant seeded ‘Sundancer’, ‘Bowie’ or ‘Cody’ buffalograss at 146 kg ha-1 from late November though late March, which allowed establishment before the following winter. Increasing seeding rate beyond 146 kg ha-1 had no effect on August buffalograss cover, regardless of seeding date. Buffalograss burs are commercially KNO3-treated and chilled to overcome dormancy. Our studies suggest commercial treatment of burs may not be necessary when dormant seeding, but should maximize germination when dormant seeding during exceptionally dry winters. Though established buffalograss can be maintained with minimal inputs, weed control is critical during the establishment period. We found the herbicides mesotrione, sulfentrazone, quinclorac, carfentrazone, simazine, amicarbazone, sulfentrazone + quinclorac, carfentrazone + quinclorac, or sulfentrazone + prodiamine applied either at seeding or at emergence were safe on ‘Bowie’ or ‘Sundancer’ buffalograss, effectively minimized weed pressure, and maximized buffalograss establishment.
Advisors: Zac Reicher and Keenan Amundsen
2015-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/95
https://digitalcommons.unl.edu/context/agronhortdiss/article/1098/viewcontent/Luqi_Li_2015.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Buffalograss
Buchloë dactyloides
Turfgrass
Warm-season
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1100
2015-12-09T23:08:58Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
MOLECULAR GENETIC ASPECTS OF IRON AND COPPER CROSS-TALK IN <i>Arabidopsis thaliana</i>
Xiang, Qingyuan
Iron (Fe) and copper (Cu) are essential micronutrients for plants and humans who consume plants. Their functions are tightly linked. For example, both of Fe and Cu work as cofactors in superoxide dismutase proteins to prevent reactive oxygen species damage. When Fe is removed from nutrient solution, plants uptake more Cu, but how plants sense and respond to Fe status is not fully understood. This thesis includes two projects that focus on Fe and Cu interaction, homeostasis and cross-talk in Arabidopsis thaliana.
Two Arabidopsis ecotypes, Kas-1 and Tsu-1, have difference in timing of Cu accumulation in rosettes under Fe deficiency. In the first study, we utilized a Kas-1 and Tsu-1 recombinant inbred line population form QTL mapping. Based on QTL composite interval mapping, one significant QTL was identified on the chromosome one [C1_23318972, C1_25175851] which explained 10% of the variation. We identified candidate genes based on their functions and amino acids differences between Kas-1 and Tsu-1. A time course experiment suggested that two candidate genes, HMA5 and ATX1, can’t account for differences between Kas-1 and Tsu-1 for timing of Cu accumulation.
Genome-wide transcriptional profiling with Illumina HiSeq technology was used to reveal Fe/Cu cross-talk gene lists. The use of SQUAMOSA Promoter Binding Protein-Like7 (SPL7) mutant plants in Fe and Cu deficiencies addressed the research hypothesis that the uptake of Cu under Fe deficiency is independent of the normal Cu uptake system, and we identified specific SPL7 regulated genes under Cu deficiency. Wild-type Col-0 and mutant spl7 showed different patterns of classic bHLH family genes bHLH38, bHLH39, bHLH100, and bHLH101. Several ETHYLENE RESPONSIVE ELEMENT BINDING FACTORS (ERFs) were downregulated in Col-0, not in spl7. The wild type Col-0 and spl7 mutant transcriptional profiling would give significant insight into Fe and Cu homeostasis.
Advisor: Brian Waters
2015-12-02T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/96
https://digitalcommons.unl.edu/context/agronhortdiss/article/1100/viewcontent/Master_thesis_2015.12.03.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
QTL mapping
Recombinant inbred lines
SQUAMOSA Promoter Binding Protein-Like7
Transcriptional profiling
superoxide dismutase
Real-time PCR
Iron
Copper
Arabidopsis
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1101
2015-12-09T23:36:12Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Evaluation of Genetic Gain for Dynamic Leaf Traits in Maize Using Field Spectroscopy
Luetchens, Jonathan
Rapid introduction of cheap and precise genotyping technology has created a void between genotypes and phenotypes in maize breeding. While detailed genetic information is easily accessible, the data are lacking robust phenotypes to be used in mapping studies like genome-wide association. As a result, high-throughput phenotyping tools are necessary to rigorously characterize specific traits. In this study, agronomic traits and an active spectrometer system were used to monitor 36 era hybrids – popular commercial maize hybrids grown from 1936 to 2012 – to discover how various traits have changed over time. In conjunction with increased grain yield of 76 kg/ha per year, modern hybrids displayed a decreased anthesis silking interval, as well as decreased stalk lodging, root lodging, plant height, ear height, and early vegetative biomass, and increased staygreen. In addition, modern hybrids displayed increased leaf chlorophyll and water contents. The 760/730 vegetation index, designed to study plant health and nitrogen uptake using the red edge region of the electromagnetic spectrum, correlated strongly to total leaf chlorophyll content (R2 = 0.64) and also displayed higher values in modern hybrids at numerous points throughout the growing season. By understanding these morphological and physiological trends of maize hybrids over time, breeders can continue to select for traits that are known to enhance yield. Moreover, this research shows that high-throughput phenotyping tools that estimate chlorophyll content can be implemented into a breeding program because the technology can detect superior cultivars.
Advisors: Aaron Lorenz and Timothy Arkebauer
2015-12-04T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/97
https://digitalcommons.unl.edu/context/agronhortdiss/article/1101/viewcontent/Thesis.LuetchensFinal.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Era Hybrids
Vegetation Indices
760/730
Chlorophyll
High-Throughput Phenotyping
Breeding
Plant Breeding and Genetics
oai:digitalcommons.unl.edu:agronhortdiss-1102
2019-03-05T16:29:03Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Effect of Genotype, Environment, and Production Packages on Yield, Agronomic Characteristics, and End-Use Quality of Winter Wheat
Bhatta, Madhav
Grain yield and end-use quality are the most important characteristics for hard red winter wheat (Triticum aestivium L.). Improvement of grain quality characteristics of grain from a given growing season and location requires systematic understanding of the genotype chosen, the production environment, and also knowing the consequence of rate and time of individual production packages such as seed treatment, seed rate, nitrogen (N) fertilization, and foliar fungicide applications. The objectives of this study were to: identify the effects of seed rate, genotype, and N top-dressed on yield, agronomic characteristics, and end-use quality of winter wheat; and to determine the effects of seed treatment and flag leaf foliar fungicide application on yield and agronomic characteristics of wheat cultivars. Two experiments were conducted at Havelock, near Lincoln, NE and the High Plains Agricultural Lab (HPAL), near Sidney, NE in 2014 and 2015 using randomized complete block design with split factorial arrangement. Overall foliar N increased grain yield, grain protein concentration, other baking quality indicators such as flour water absorption, peak height, tail area, weakening slope, and depressed grain volume weight, mixing time, and tolerance. Similarly, increased seed rate improved grain yield, seed weight, grain volume weight, flour yield, mixing time, and mixing tolerance. Increased seed rate reduced grain protein, flour water absorption, tail area, peak height, and weakening slope. Seed treated with EverGol Energy and Gaucho showed improved seedling emergence, leaf greenness, grain yield, and seed weight. Application of foliar fungicide at flag leaf stage improved grain yield, seed weight, and leaf area. Among the six genotypes evaluated, ‘Settler CL’ and ‘Freeman’ had the highest overall grain yield. The study demonstrated the importance of seeding rate and the existence of a wider than expected tolerance range for seeding rate. The study also demonstrated the importance of in-season nitrogen top dress and foliar fungicide application to increased winter wheat grain yield and grain quality in Nebraska. However, further research is recommended to fine-tune the factors and interdependence of response in relation to a specific location, season or the prevailing weather condition, and the specific attribute of the genotype seeded.
Adviser: Teshome H. Regassa
2015-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/98
https://digitalcommons.unl.edu/context/agronhortdiss/article/1102/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Agronomy and Crop Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1103
2016-02-05T20:47:29Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Goss's Bacterial Wilt Development and <i>Clavibacter michiganensis</i> subsp. <i>nebraskensis</i> Interactions with Spray Adjuvants
Schlund, Sarah A
Goss’s bacterial wilt and leaf blight of corn (Zea mays L.), causal agent Clavibacter michiganensis subsp. nebraskensis, was first confirmed in Dawson County, NE in 1969. Disease incidence decreased in the 1980’s due to various management strategies and disease developed sporadically until the early 2000’s when it re-emerged and was economically important. A Midwest, multistate survey conducted in 2011 suggested farming practices that may have contributed to the pathogen’s re-emergence. The use of agricultural pesticides was associated with Goss’s wilt. Since spray adjuvants are often used with pesticides, and physical characteristics of these adjuvants may enable infection of the leaf by epiphytic C. michiganensis subsp. nebraskensis, greenhouse and field studies were conducted to assess the effect of adjuvants on Goss’s wilt severity. A preliminary greenhouse study was conducted to determine if an epiphytic population of C. michiganensis subsp. nebraskensis could be established and initiate infection. The population became established and disease severity was higher when plants were less mature. To evaluate the effect of adjuvants on disease development with adjuvants, a greenhouse study was established. Adjuvants tested did not cause a consistent increase in disease severity between trials. An inhibition test was designed to determine if spray adjuvants inhibited bacterial growth in vitro at different concentrations. Results showed minimal inhibition at label rate for NIS, and consistent inhibition at 10X label rate for NIS with some inhibition for MSO and COC. Field studies were conducted in southwest Nebraska in 2014 and 2015. Disease severity was lower in adjuvant treatments in 2014. In 2015, no differences for disease severity or systemically infected plants were detected among treatments. These data indicate that spray adjuvants commonly used in corn production are not causing an increase in Goss’s wilt severity. Rather, adjuvants at higher rates may reduce the population of epiphytic C. michiganensis subsp. nebraskensis to below levels required for infection. Further research is needed before recommending non-label rate of these adjuvants under field conditions.
Advisors: Tamra Jackson-Ziems, Greg Kruger
2015-12-01T08:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/99
https://digitalcommons.unl.edu/context/agronhortdiss/article/1103/viewcontent/auto_convert.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
Goss's wilt
corn
adjuvants
disease
severity
inhibition
spray
Agronomy and Crop Sciences
Plant Sciences
oai:digitalcommons.unl.edu:agronhortdiss-1105
2016-04-26T14:25:22Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Cover Crop Mixture Diversity and Function
Florence, Angela
The objective of this study was to evaluate the effect of cover crop mixture diversity on cover crop function. Specifically, this study evaluated the effect of cover crop species and functional richness on aboveground biomass productivity, weed suppression, soil nutrient retention, soil microbial community characteristics, and performance stability. Twenty to forty cover crop treatments were replicated three to four times at eleven sites across southeastern Nebraska using a pool of eighteen species representing three cover crop species each from six pre-defined functional groups: cool-season grasses, cool-season legumes, cool-season brassicas, warm-season grasses, warm-season legumes, and warm-season broadleaves. Each species was planted in monoculture and the most diverse treatment contained all eighteen species. Remaining treatments represented intermediate levels of cover crop species and functional richness. Cover crop planting dates ranged from late July to late September with both cover crop and weed aboveground biomass being sampled prior to winterkill. Soil samples were taken in the following spring and analyzed for soil extractable nitrate, phosphorus, potassium, sulfate, and chloride as well as extracted for fatty acid methyl esters to characterize soil microbial biomass and community structure. Performance stability was assessed by evaluating the variability in cover crop biomass for each treatment across plots within each site. While increasing cover crop mixture diversity increased average aboveground biomass productivity, I argue that this was simply the result of the average performance of the monocultures being drawn down by low yielding species rather than due to niche complementarity or increased resource use efficiency. Furthermore, while increases in cover crop mixture diversity were often correlated with increases in weed suppression, increases in soil nutrient retention, increases in soil microbial biomass, alterations in soil microbial community structure, and increases in performance stability, I argue that this was a result of diversity co-varying with aboveground biomass, and that differences in aboveground biomass rather than differences in diversity drove the differences observed in weed suppression, nutrient retention, soil microbial community characteristics, and stability. The results of this study contradict many popular hypotheses regarding the relationship between plant mixture diversity and function.
Advisor: John L. Lindquist
2016-05-01T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/100
https://digitalcommons.unl.edu/context/agronhortdiss/article/1105/viewcontent/Florence___Cover_crop_mixture_diversity_and_function.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
cover crop
plant mixture
diversity
biomass productivity
invasibility
weed suppression
soil nutrient retention
soil microbial biomass
soil microbial community structure
stability
Agronomy and Crop Sciences
Biodiversity
Weed Science
oai:digitalcommons.unl.edu:agronhortdiss-1106
2016-04-28T15:53:41Z
publication:agronhortdiss
publication:unletdreports
publication:ag_agron
Biology, Gene Flow, and Management of Glyphosate-Resistant Common Waterhemp (<i>Amaranthus rudis</i> Sauer) in Nebraska
Sarangi, Debalin
Common waterhemp is the most troublesome weed in the midwestern United States. Growers from Nebraska reported failure to control common waterhemp following sequential applications of glyphosate in glyphosate-tolerant corn and soybean, which led to moderate to severe yield loss; justifying the need to confirm resistance and study the biology and management of common waterhemp. The objectives of this research were: 1) to confirm the presence of glyphosate-resistant (GR) common waterhemp biotypes in Nebraska and to evaluate their sensitivity to herbicides belonging to alternative sites-of-action; 2) to evaluate the response of common waterhemp to water stress; 3) to quantify pollen-mediated gene flow from GR common waterhemp under field conditions; and 4) to evaluate different herbicide programs for season-long control of glyphosate-resistant common waterhemp in glyphosate-tolerant soybean. Greenhouse dose-response studies conducted to evaluate the response of suspected GR common waterhemp biotypes collected from seven eastern Nebraska counties (Antelope, Dodge, Fillmore, Lancaster, Pawnee, Seward, and Washington) revealed that the biotypes were 3- to 39-fold resistant to glyphosate. The GR biotypes also showed a reduced sensitivity to acetolactate synthase (ALS)-inhibiting herbicides (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, and thifensulfuron-methyl). Experiments conducted to evaluate the response of common waterhemp to water stress suggested that degree and duration of water stress can adversely affect the growth and seed production of common waterhemp. Highest plant height (≥ 150 cm), growth index (≥ 3.8 × 105 cm3), and seed production (> 34,000 seeds plant-1) were recorded with 100% pot water content applied at 2-d intervals. Pollen-mediated gene flow studies from GR to GS biotypes were conducted under field conditions using a Nelder wheel design. Frequency of gene flow was found to be highest (up to 0.77) at the closer distances (0 to 0.1 m); whereas gene flow frequency declined by 50% at < 2.5 m and 90% at distances < 90 m from the pollen source. Field experiments conducted for management of GR common waterhemp in soybean showed that preemergenece (PRE) followed by postemergence (POST) herbicide programs with multiple sites-of-action provided season-long control of GR common waterhemp and resulted in the highest soybean yield compared to the POST-only herbicide programs.
Adviser: Amit J. Jhala
2016-04-19T07:00:00Z
text
application/pdf
https://digitalcommons.unl.edu/agronhortdiss/101
https://digitalcommons.unl.edu/context/agronhortdiss/article/1106/viewcontent/Debalin_Sarangi_2016_REVISED.pdf
Department of Agronomy and Horticulture: Dissertations, Theses, and Student Research
DigitalCommons@University of Nebraska - Lincoln
EPSPS gene amplification
Generalized nonlinear model
Growth index
Multiple resistance
Pollen dispersal
Resistance management
Agricultural Science
Agriculture
Agronomy and Crop Sciences
Genomics
Life Sciences
Weed Science
191920/oai_dc/100//