Identification and molecular mapping of a major gene conferring resistance to Phytophthora sansomeana in soybean ‘Colfax’

Abstract

Abstract Phytophthora root rot (PRR) is one of the most important diseases in soybean (Glycine max). PRR is mainly caused by Phytophthora sojae, but recent studies showed that P. sansomeana is another causal agent of PRR with more aggressive symptoms, especially in seeds and seedlings. Unlike P. sojae which can be effectively managed by Rps genes, no known resistance genes have yet been reported for P. sansomeana. Our previous study screened 470 soybean germplasm for resistance to P. sansomeana and found that soybean ‘Colfax’ (PI 573008) carries major resistance to the pathogen. In this study, we crossed ‘Colfax’ with a susceptible parent ‘Senaki’ and developed three mapping populations with a total of 234 F2:3 families. Inheritance pattern analysis indicated a 1:2:1 ratio for resistant: segregating: susceptible lines among all the three populations, indicating a single dominant gene conferring the resistance in ‘Colfax’ (designated Rpsan1). Linkage analysis using extreme phenotypes anchored Rpsan1 to a 30Mb region on chromosome 3. By selecting 9 polymorphic SNP markers within the region, Rpsan1 was genetically delimited into a 21.3 cM region between Gm03_4487138_A_C and Gm03_5451606_A_C, which corresponds to a 1.06 Mb genomic region containing 9 NBS-LRR genes based on Gmax2.0 assembly. The mapping results were then validated using two breeding populations derived from ‘E12076T-03’ × ‘Colfax’ and ‘E16099’ × ‘Colfax’. Marker-assisted resistance spectrum analyses with 9 more isolates of P. sansomeana indicated that Rpsan1 carries a broad resistance to P. sansomeana isolates and has strong merit in protecting soybean from PRR in the future.