Agronomy and Horticulture Department


Date of this Version

Spring 5-20-2016


Sserunkuma, H. 2016. Identification of QTLs for resistance against Rhizoctonia solani and Phoma glycinicola in soybeans (MS thesis). University of Nebraska-Lincoln.


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor George L. Graef. Lincoln, Nebraska: May, 2016

Copyright © 2016 Herbert Sserunkuma


A QTL (Quantitative trait locus) is a chromosome location of a gene controlling a specific phenotypic trait. The trait maybe governed by multiple genes. Fungal pathogens are responsible for over 50% of all soybean diseases. Rhizoctonia solani Kühn causes seedling dumping off, root and hypocotyl rots and other disease in soybeans. Phoma glycinicola de Gruyter & Boerema causes Red leaf blotch disease, predominantly in Sub-Saharan Africa. There is no reported complete resistance against these fungal pathogens in soybeans. Reaction to R.solani is reportedly a quantitative trait controlled by major and minor genes. Three QTLs contributing to reaction to R. solani were reported in a study using SSR markers on chr 6 (Satt 177), chr 6 (Satt 281) and chr 7(Satt 245) that explained 7%, 11% and 6.8% respectively. The objective of this study was to identify QTLs that control reaction to R. solani and P. glycinicola using RIL populations genotyped with the 1,536 GoldenGate SNP assay and also identify similarity and co-localization in QTL regions controlling resistance to other fungal pathogens. The RIL populations in this study were used to map QTL for resistance to Sclerotinia sclerotiorum (Lib.) de Bary. Two RIL populations UX990 (Williams 82 X DSR 173) and UX988 (Williams 82 X Corsoy 79) segregating for the traits were evaluated. Data for the UX990 population was used for QTL analysis. This population had 90 lines and 350 polymorphic SNP markers covering about 1917.2 cM of the 3000 cM according to Hyten et al. (2010). A significant QTL was identified on Chr 10 (LG-O) that explained 43.1% of the variation in the response to R. solani and was located in the same region as QTLs reported for reaction to two other fungal pathogens, Sclerotinia sclerotiorum and Phytophthora spp. Analysis of P. glycinicola data identified a significant major effect QTL on Chr 2 at 32.4 cM and a minor effect QTL on Chr 15 at position 97.3cM. These regions also contain QTL regions contributing to reactions to fungal pathogens Sclerotinia sclerotiorum, Phytophthora sojae and Fusarium spp. Further studies are required to verify findings of this research.

Advisor: George L. Graef