Inheritance of Phomopsis Seed Decay Resistance in Soybean PI 417479

Phomopsis seed decay (PSD) is part of a major soybean [ Glycine max (L.) Merr.] fungal disease complex found in the USA and other areas of the world. The predominant disease organism, Phomopsis longicolla T.W. Hobbs, can cause reductions in seed quality and germination. While some chemical and cultural control measures exist to reduce losses due to this disease, genetic resistance would be desirable. An extensive screening project has identified PI 417479 as resistant to PSD. To most efficiently transfer the disease resistance found in PI 417479 to improved cultivars, knowledge of the inheritance of the trait is needed. Crosses were made between PI 417479 and each of two PSD‐susceptible genotypes, ‘Agripro 350’ and PI 91113. Five generations (F 1 , F 2 , F 3 , B 1 , and B 2 , in which B 1 , represents a backcross between the F 1 and the resistant parent and B 2 represents backcross between the F 1 and the susceptible parent) were generated for each cross. These were tested in 1990 in the field at two locations near Columbi, MO. A sample of seeds from each plant was bioassayed to determine percent PSD incidence. Seeds from plants showing various degrees of infection in 1990 were progeny tested in 1991. Although environment was found to strongly influence disease incidence, results indicate that the PSD resistance found in PI 417479 is controlled by two complementary dominant nuclear genes. We concluded that the resistance genes can be transferred using a backcross procedure.