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Genetic Implications of the Susceptibility of Kent Soybean to Cercospora sojina. H. R. Boerma, Department of Agronomy, University of Georgia, Athens 30602; D. V. Phillips, Department of Plant Pathology, Georgia Experiment Station, Experiment 30212. Phytopathology 73:1666-1668. Accepted for publication 25 July 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/Phyto-73-1666.

Seven different sources of cultivar Kent soybean (Glycine max) seed were obtained from different states in the USA. Separate plants from each source were inoculated with races 2 and 5 of Cercospora sojina. Kent was found to be a mixture of reaction types to race 5 in six of the seven sources and to race 2 in two of seven sources. In general, Kent was resistant to race 2 and susceptible to race 5. When plants of Kent and cultivar Bragg were inoculated with race 5 and single-lesion isolates from both cultivars were used to inoculate a group of differential cultivars, the results indicated that the biotype infecting Kent was the same as on Bragg. The understanding of the reaction of Kent to races 2 and 5 indicated that the Rcs2 gene in Kent for resistance to race 2 cannot condition resistance to race 5. The reactions to races 2 and 5 of F2 plants of the Blackhawk x Davis cross indicated that the gene in Davis for resistance to race 5 also conditioned resistance to race 2. The segregation ratio among F3 lines for reaction to race 2 from the Davis x Kent cross indicated the gene in Davis and Rcs2 were at different loci. Thus, the single dominant gene in Davis for resistance to races 2 and 5 should be assigned the symbol, Rcs3.

Additional keywords: disease resistance, frogeye leafspot, inheritance.