Phenotypic and Molecular Evaluation of Soybean Germplasm Resistant to Frogeye Leaf Spot.

Frogeye leaf spot (FLS), caused by Cercospora sojina Hara, is an important foliar disease of soybean, Glycine max (L.) Merr., in many production areas of the United States. The characteristic lesions caused by the pathogen result in reduced photosynthetic area and in premature defoliation. Using resistant varieties is the most cost effective means to reduce yield loss.. Twenty-four putative resistant lines were evaluated for their phenotypic reaction to C. sojina and their yield performance in a honeycomb design in three divergent locations of southern Illinois. In addition, one-hundred and twenty microsatellites (SSRs) were screened across the soybean genotypes to assess genetic variability and to identify any possible associations with phenotypic characteristics that are related to FLS resistance. Several statistical methods were applied to identify candidate SSR loci that may be valuable for mapping FLS resistance: Multi-dimensional scaling and cluster analyses to reveal different groups of genotypes, Shannon entropy for defining single- and multi-locus diversity as well as SSR informativeness, along with AMOVA and Kruskal-Wallis one-way ANOVA. The phenotypic diversity analysis under nil-competition along with the molecular study provide valuable information for soybean breeders designing strategies for incorporating resistance and for molecular biologists wishing to create recombinant inbred line populations to map these traits.