Genetic analysis of frogeye leaf spot resistance in PI54610 and Peking soybean

Frogeye leaf spot (FLS) of soybean [Glycine max (L.) Merr.] is caused by th e fungus Cercospora sojina Hara. The fungus is ubiquitous, but only problem atic in hot humid soybean-producing regions such as Brazil, China, Nigeria, and the southern USA. Significant yield losses (10-50%) are commonly assoc iated with FLS epidemics. The quantification of unique alleles for resistan ce within the southern germplasm pool is an essential step toward developin g a more usable set of differential genotypes and thereby clarifying the ra ce situation within the C. sojina-soybean interaction. Our objective was to determine the inheritance of resistance to FLS in PI54610 and Peking and t heir allelic relationship to Rcs(3). 'Lee' soybean was used as a susceptibl e parent for crosses and control in all experiments. Parents and Fl seedlin gs were inoculated with a C. sojina spore suspension in the greenhouse or f ield and then rated for disease development 14 to 21 d later. On the basis of segregation ratios (3:1 resistant/susceptible in Peking x Lee and PI5461 0;< Lee, and 15:1 in 'Davis' x Peking and PI54610 x Peking), we found resis tance in Peking was determined by a single dominant gene nonallelic to Rcs( 3). We also found, based on nonsegregation of resistance within the Davis x PI54610 population, that PI54610 has the same gene as in Davis (Rcs(3)) Re sistance in Peking should be considered unique for the purpose of race diff erentiation and as a commercial source of resistance to FLS should Rcs(3) f ail.