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White mold/dry bean: Population structure and phenotypic variation of Sclerotinia sclerotiorum from dry bean in the USA

Sydney Everhart: University of Nebraska

<div>The ascomycete pathogen and causal agent of white mold on dry bean, <em>Sclerotinia sclerotiorum</em>, is a necrotrophic pathogen on over 400 known host plants. Currently, there are no known cultivars of dry bean with complete resistance to white mold. For over 20 years, bean breeders have used white mold screening nurseries (WMSN) with natural populations of <em>S. sclerotiorum</em> to screen new cultivars for resistance. It is thus important to know if the genetic diversity in populations of <em>S. sclerotiorum</em> within these nurseries a) reflect the genetic diversity of the populations in the surrounding region and b) are stable over time. Furthermore, previous studies have investigated the correlation between mycelial compatibility groups (MCG) and multilocus haplotypes (MLH), but none have formally tested these patterns. We genotyped 366 isolates of <em>S. sclerotiorum</em> from producer fields and WMSN surveyed over 10 years in 2003–2012 representing 11 states in the United States of America, Australia, France, and Mexico at 11 microsatellite loci resulting in 165 MLHs. Populations were loosely structured over space and time based on analysis of molecular variance and discriminant analysis of principal components, but not by cultivar, aggressiveness, or field source. Our study suggests that breeders should continue to test dry bean lines in several WMSN across the USA to account for both the phenotypic and genotypic variation that exists across regions.</div>