| Abstract: | Phomopsis seed decay (PSD), caused primarily by the fungus Phomopsis longicolla Hobbs, is one of the most serious seed diseases of soybean [Glycine max (L.) Merr.]. Plant introduction (PI) 417479 has demonstrated resistance to PSD in a wide array of environments. This resistance has been interpreted to support models of qualitative inheritance; however, the lack of discrete separation between resistant and susceptible classes indicates that resistance to this disease may be genetically complex or markedly influenced by environmental factors. This study was conducted to identify genomic regions associated with resistance to PSD using random restriction fragment length polymorphism (RFLP) markers. PI 417479 was crossed with each of two susceptible soybean cultivars, Agripro AP 350 and Williams 82. In 1993 and 1994, F(2) and F(2)-derived lines for each population were scored for PSD incidence near Columbia, MO. Screening based on 188 RFLP markers in all combinations with five restriction enzymes identified 43 polymorphic markers in the PI 417479 x AP 350 population and 26 polymorphic markers in the PI 417479 x Williams 82 population. Marker A708, which identifies a genomic region in linkage group F, was associated with PSD resistance in both populations and both years. This marker, when used in combination with restriction enzyme DraI, explained from 21.0 to 62.2% of the phenotypic variation in PSD disease response. The use of marker A708 could enhance efforts to incorporate resistance to PSD into improved soybean cultivars. |