Identifying resistance to Phytophthora sojae in selected soybean accessions using RFLP techniques

Phytophthora sojae (Kauffmann and Gerdemenn) is the causal agent of phytophthora root and stem rot of soybean [Glycine max (L.) Merr.]. A disease outbreak in favorable environmental conditions has the potential to inflict 100% yield loss. Soybean accessions from central China offer unique genetic variability and are potential sources for novel genes conferring phytophthora resistance. Approximately 500 accessions have been classified for reaction to races 1, 3, and 7 of P. sojae. Eighteen accessions were selected that were resistant to races 1 and 3 and susceptible to race 7. RFLP markers linked to resistance alleles were used to compare the accessions to isolines with known Rps alleles. Restriction fragment length polymorphism (RFLP) results were supported with greenhouse hypocotyl inoculations with zoospores of races 1, 3, 5, 8, 12, 13, and 25. One plant introduction (PI) was found likely to possess Rps1a, five possibly possessed Rps2, seven could carry Rps3, and four were found possibly to possess Rps4. Evidence of multigene combinations were detected in eight accessions. Unique RFLP bands and hypocotyl inoculation reactions were discovered in PIS 567343, 567530, 567572A, 567574A, 567583A, 567764, and 567766, implying possible presence of novel Rps alleles. Knowledge of which Rps allele combinations are present in these accessions will allow for integration of the novel resistance into modern cultivars.