The invention provides soybean plants having a novel determinant, Rps8, for resistance to Phytophthora sojae. The invention also provides methods for identifying germplasms that are either heterozygous or homozygous for Rps8 using marker assisted selection. Genetic markers with known chromosomal location that are associated with the Rps8 gene are used to confirm Rps8-derived Phytophthora sojae resistance in germplasms. Marker assisted selection also used when introgressing Rps8-derived soybean Phytophthora sojae resistance into non-resistant soybean germplasm or less resistant soybean germplasms.