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Association Mapping of Sclerotinia sclerotiorum mid-stalk rot virulence on two sunflower inbred lines

Kassaye Belay: North Dakota State University

<div><em>Sclerotinia sclerotiorum </em>is one of the most destructive pathogens of sunflower in the United States and worldwide. This fungal pathogen has a remarkably broad host range of over 400 dicot plants. However, little is currently known about the virulence strategies that allow <em>S. sclerotiorum </em>to successfully infect a wide range of plant hosts. The goal of our project is to identify <em>S. sclerotiorum </em>virulence determinants such as protein, small molecule, and small RNA effectors that contribute to disease development on sunflower. We have four main objectives; 1) evaluation of the virulence of a large and diverse collection of <em>S. sclerotiorum </em>isolates on mid-stalk tissues of sunflower; 2) genotyping-by-sequencing <span>of <em>S. sclerotiorum</em></span> isolates to facilitate association mapping; 3) association mapping to identify candidate genetic factors influencing virulence in <em>S. sclerotiorum</em>; 4) <em></em>evaluation of candidate <em></em>genes using direct knockout and subsequent evaluation of mutant strains for virulence. We have assembled a collection of 234 diverse <em>S. sclerotiorum </em>isolates and completed the phenotyping of these isolates for virulence on stems of USDA sunflower inbred line HA207. Additionally, we are phenotyping those isolates on a second, partially inbred line, HA441. We performed genotyping-by-sequencing for 227 isolates to facilitate association mapping. We are also currently working on direct knockout of five candidate genes, using gene replacement and subsequent evaluation of mutant <em>S. sclerotiorum</em> strains for virulence on the two inbred lines of sunflower. Our initial results indicate that <em>S. sclerotiorum </em>isolates exhibit significant differences in virulence on sunflower, indicating the potential for our method to successfully identify genetic factors underlying these differences.</div>