Inheritance of resistance to phomopsis seed decay in soybean PI 80837 and MO/PSD-0259 (PI 562694)

Phomopsis seed decay [PSD; caused by Diaporthe phaseolorum var. sojae (Lehman) Wehmeyer, Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. caulivora Athow & Caldwell, and Phomopsis longicolla Hobbs) reduces quality of soybean [Glycine mar (L.) Merr.] seed when moist conditions and warm temperatures occur during seed development and maturation. Control of PSD by genetic resistance has not been well explored. Of the genotypes reported with PSD resistance, PI 417479 and PI 80837 have received the most study. The PSD-resistant line MO/PSD-0259 derives its resistance from PI 417479. Objectives of this research were to characterize the inheritance of PSD resistance in PI 80837 and to determine if it differs from resistance in MO/PSD-0259. PI 80837 was crossed with PSD-susceptible 'Agripro 3501 (AP 350); PSD-susceptible PI 91113; and with MO/PSD-0259. Populations and lines were screened in the field, and Phomopsis infection was assayed by plating seed. Seed infection of reciprocal F, plants of AP 350 X PI 80837 was not different from that of PI 80837. Data from F-2 populations of AP 350 X PI 80837 and PI 91113 X PI 80837; and F-2:3 lines from AP 350 X PI 80837 fit models for a single dominant gene in PI 80837 that confers PSD resistance. F-2 population data from AP 350 X MO/PSD-0259 also fit a model for single dominant gene resistance in MO/PSD-0259, and data from an F-2 population and F-2:3 lines of PI 80837 X MO/PSD-0259 fit a model for two different dominant genes. These results show that PSD resistance in PI 80837 is conferred by a single dominant gene under nuclear control that is different from the gene in MO/PSD-0259.