Additional Genes for Resistance to Frogeye Leaf Spot Race 5 in Soybean

Abstract

Frogeye leaf spot (caused by Cercospora sojina Hara) is a common foliar disease of soybean ( Glycine max L. Merr.) in the southeastern USA. Three major dominant genes ( Rcs 1 , Rcs 2 , and Rcs 3 ) have been identified that confer resistance to frogeye leaf spot. Our objective was to determine the inheritance and possible allelism to Rcsa of genes for resistance in ‘Lee’, ‘Stonewall’, and ‘Ransom’. Lee, Stonewall, and Ransom were all intercrossed, crossed with ‘Davis’, which has Rcs 3 , and crossed with known susceptibles. F 2 plants of crosses were inoculated with a spore suspension of race 5 of C. sojina , placed in a moist chamber for 2 to 3 d, and identified as susceptible or resistant based on leaf symptoms 14 d after inoculation. All F 2 populations segregated 3 resistant : I susceptible or 15 resistant : 1 susceptible. This indicated different dominant genes for resistance to race 5 in Ransom, Stonewall, and Lee and that each was nonallelic to Rcs 3 and to each other.