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Phytophthora root and stem rot caused by Phytophthora sojae Kaufm. & Gerd. is one of the most damaging diseases of soybean, with an estimated worldwide loss of revenue of $1-2 billion per year. Management is principally done by planting cultivars with resistance. Monogenic race specific resistance genes to P. sojae (Rps) confer resistance to pathogen strains carrying the virulence gene (Avr). The durability of a deployed gene in the field is limited by generation of new virulence pathotypes of P. sojae that can evade the Rps-mediated immunity. Rps8 was identified in the South Korean landrace PI 399073 and to facilitate its introduction in commercial cultivars, molecular markers closely linked with the locus are required. These markers can also assist in the cloning of this gene, allowing us to enrich the knowledge on: the genomic organization and structure of Rps genes and the study of soybean-P. sojae race specific interactions. In this study, resistance to P. sojae was evaluated on eight Williams (rps8/rps8) x PI 399073 (Rps8/Rps8) populations, and one PI 399073 (Rps8/Rps8) x PI 408211B (multiple Rps genes) population. In the Williams x PI 399073 crosses, phenotypic ratios were highly skewed with an excess of Rps8/Rps8 lines, maintenance of heterozygosity and few rps8/rps8 lines. A graphical genotype was generated from three Williams x PI 399073 BC 4 F 2: 3 populations as Rps8 was associated with a 2.23 Mbp region on chromosome 13. The linkage of this region with Rps8 was confirmed in BC 4 F 4: 5 generation. In a PI 399073 x PI 408211B F 4: 5 a different locus which conferred resistance to P. sojae isolate Butmu was …