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Mechanism of resistance, gene flow, and integrated management of ragweeds (Ambrosia) in Nebraska
Common ragweed (Ambrosia artemisiifolia L.) and giant ragweed (Ambrosia trifida L.) are native annual broadleaf weeds in the United States found in diverse agroecosystems, roadsides, and wastelands. They are economically important weed species in the Midwest and sources of pollen allergies. Confirmation of glyphosate-resistant (GR) common and giant ragweed in Nebraska justified the need to determine the mechanism of resistance, dispersal of resistance genes via pollen, and to develop an integrated management program. The objectives of this research were to: 1) determine the mechanism of glyphosate resistance in a common ragweed biotype from Nebraska; 2) evaluate the effect of varying growth temperatures on efficacy, absorption, and translocation of glyphosate or 2,4-D in GR and susceptible (GS) common and giant ragweed biotypes; 3) quantify the pollen-mediated gene flow (PMGF) from GR to GS giant ragweed under field conditions; and 4) evaluate the integrated management of giant ragweed with preplant tillage followed by PRE and/or POST herbicide programs in corn and soybean. Experiments were conducted to determine mutation(s), and amplification of the EPSPS gene (target-site mechanisms), as well as differences in uptake/translocation and the metabolism of glyphosate (non-target site mechanisms) between GR and known GS common ragweed biotypes. The results suggest that a slow rate of glyphosate absorption and translocation likely prevents the build-up of the minimum inhibitory glyphosate concentration required at the target site, resulting in resistance to glyphosate in a common ragweed biotype from Nebraska. Experiments conducted to study the effect of temperature on the efficacy of 2,4-D or glyphosate in common and giant ragweed suggested that control improved at warm temperatures (29/17 0C d/n) compared to cooler temperatures (20/11 0C d/n) due to increased translocation in common ragweed, and increased absorption and/or translocation in giant ragweed biotypes studied. Studies on PMGF from GR to GS giant ragweed were conducted under field conditions using glyphosate resistance as a phenotypic marker. The highest frequency of gene flow (0.43 to 0.68) was detected at closer distances (< 0.5 m) and 50% reduction in gene flow occurred at < 7 m from the pollen source. Field experiments conducted to evaluate the integrated management of GR giant ragweed suggested that integration of preplant tillage would provide an alternate method for early season control of giant ragweed; however, follow-up application of herbicides are needed for season-long control in corn and soybean.^
Ganie, Zahoor Ahmad, "Mechanism of resistance, gene flow, and integrated management of ragweeds (Ambrosia) in Nebraska" (2016). ETD collection for University of Nebraska - Lincoln. AAI10245230.