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Comparison of Quantitative Disease Resistance Loci in Soybean Towards Soil Borne Root Pathogens

Anne Dorrance: The Ohio State University, Dept. of Plant Pathology

<div>Several studies in the past decade have raised awareness of the diversity of species that contribute to soybean stand loss as well as the diversity within species that can impact management. In addition to <em>Phytophthora sojae</em>, more than 40 species of <em>Pythium</em>, <em>Phytophthora sansomeana</em>, and <em>Fusarium graminearum</em> are now recognized as pathogens of soybean. Over the past two decades, numerous sources of resistance have been identified, and the purpose of our studies was to identify the QTL and mechanisms that contribute to resistance. Four recombinant inbred line (RIL) populations from the soybean Nested Association Mapping population were segregating for resistance to <em>P. sojae</em> and one or more <em>Pythium</em> spp. Disease resistance for <em>P. sojae</em> was measured in RILs by lesion length with a tray test and root rot or final root weight with a cup assay for <em>Pythium</em> spp. Numerous QTL have been identified; however, the majority are minor and contribute to less than 10% of the phenotypic variation. In addition, QTL-pathogen specificity within each population was also identified. These results have implications on future breeding efforts to expand the resistance spectrum towards more pathogens. Cultivars bred solely via marker assisted selection will require perfect markers, which are developed from the genes that contribute to a trait of interest</div>