P-554 - Genetic diversity and population structure of historical and current isolates of Cercospora sojina collected within 42 years

Frogeye leaf spot (FLS), caused by Cercospora sojina, is a major foliar soybean disease, particularly in the southern U.S., responsible for 10–60% annual yield losses in key production regions such as the U.S., Brazil, and China. While preventative fungicide applications are helpful, breeding resistant varieties remains the most effective and economical management strategy. Three genetic loci including Rcs1, Rcs2, and Rcs3 have been named to provide resistance to frogeye leaf spot in soybean, with Rcs3 conferring broad resistance to all known U.S. C. sojina races. However, the genetic diversity of C. sojina has led to the emergence of new virulent isolates capable of overcoming host resistance. In this study, the genetic diversity among 178 C. sojina isolates collected across 11 U.S. states, Brazil, China, and Nigeria over 42 years was analyzed using 686 SNPs. The analysis identified moderate to high genetic diversity (0.1–0.4 G_ST) within C. sojina populations, indicating the pathogen’s adaptability to selection pressures and the potential risk to soybean host plant resistance. Population structure analysis using DAPC and STRUCTURE identified 14 C. sojina populations that clustered based on collection year, not geography. Greenhouse assays are currently being conducted to correlate C. sojina genetic diversity and virulence phenotypes with soybean resistance and will be used to facilitate the development of genetic markers for early detection of C. sojina to help identify resistance genes that are effective against current C. sojina populations.