Inheritance of Resistance to Phytophthora megasperma f. sp. glycinea in a Soybean Plant Introduction. Alice C. Layton, Graduate Research Assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. K. L. Athow, Professor, and F. A. Laviolette, Associate Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Plant Dis. 68:1080-1083. Accepted for publication 4 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-1080.

Inheritance of resistance to Phytophthora megasperma f. sp. glycinea was studied in a soybean (Glycine max) plant introduction (PI 157409) that was resistant to races 1 through 16 of the fungus. PI 157409 was crossed with Harosoy, Mukden, Sanga, PI 546151, Williams 82, PI 86972-1, and PRX27-108. The F₂ populations and the F₃ families of each cross were inoculated with races 1, 2, 3, 4, 5, 7, and 9 of the fungus. PI 157409 had two genes for resistance: Rps₁^b, which gives resistance to races 1, 3, 4, 5, 7, and 9 and susceptibility to race 2; and Rps₄, which gives resistance to races 1, 2, 3, and 4 and susceptibility to races 5, 7, and 9. This is the first soybean strain in which the gene combination Rps₁^b Rps₄ has been reported. The combination is useful because the genes Rps₁^b Rps₄ confer resistance to all reported races, 1 through 22, of P. megasperma f. sp. glycinea.