Restriction fragment length polymorphism analysis of resistance to Phomopsis seed decay and purple seed stain in soybean PI 417479

Phomopsis seed decay (PSD), caused primarily by the fungus Phomopsis longicolla (Hobbs), is one of the most serious diseases of soybean (Glycine max (L.) Merr.) seeds. High relative humidity and/or rain and mild to warm temperature near physiological maturity favor disease development. Phomopsis seed decay incidence can greatly reduce the seed as well as grain quality.;Plant introduction (PI) 417479 demonstrated resistance to PSD in a wide array of environments. Resistance to PSD in PI 417479 was suggested to be controlled by two complementary dominant genes. However, accurate identification of resistant genotypes is hindered by environmental factors.;In order to identify genomic regions associated with resistance to PSD incidence, PI 417479 was crossed with each of two susceptible soybean cultivars AP 350 and Williams 82. For each population, F;Only marker A708 was consistently associated with PSD resistance in each population and each year. The proportion of the phenotypic variation accounted for by this marker ranged from 21.0 to 62.2%. In 1994, purple seed stain caused by Cercospora kikuchii (T. Matsu. & Tomoyasu) Gardner was also scored in the PI 417479 x AP 350 population. A885 in linkage group G was associated with purple seed stain incidence and accounted for 41.1% of the phenotypic variation.;Our research showed a consistent association between A708 and quantitative trait loci for resistance to PSD in contrasting environmental conditions and different genetic backgrounds. A marker-assisted backcross program can be successfully performed using A708 as a selective marker to introgress partial resistance to PSD into elite soybean germplasm.