Soybean Phytophthora Resistance Gene Rps8 Maps Closely to the Rps3 Region

Root and stem rot is one of the major diseases of soybean. It is caused by the oomycete pathogen Phytophthora sojae. A series of resistance genes (Rps) have been providing soybean with reasonable protection against this pathogen. Among these genes, Rps8, which confers resistance to most P. sojae isolates, recently has been mapped. However, the most closely linked molecular marker was mapped at about 10 cM from Rps8. In this investigation, we attempted to develop a high-density genetic map of the Rps8 region and identify closely linked SSR markers for marker-assisted selection of this invaluable gene. Bulk segregant analysis was conducted for the identification of SSR markers that are tightly linked to Rps8. Polymorphic SSR markers selected from the Rps8 region failed to show cosegregation with Phytophthora resistance. Subsequently, bulk segregant analysis of the whole soybean genome and mapping experiments revealed that the Rps8 gene maps closely to the disease resistance gene-rich Rps3 region. Soybean root and stem rot, caused by the oomycete pathogen Phytophthora sojae, is one of the most important diseases of soybean. It causes nearly $200 million in annual yield losses (Wrather et al. 2001). A series of Rps genes have been extensively used in protecting soybean from thi