Molecular mapping of the gene(s) conferring resistance to Soybean mosaic virus and Bean common mosaic virus in the soybean cultivar Raiden

Both Soybean mosaic virus (SMV) and Bean common mosaic virus (BCMV) can induce soybean mosaic diseases. To date, few studies have explored soybean resistance against these two viruses simultaneously. In this work, Raiden, a cultivar resistant to both SMV and BCMV, was crossed with a susceptible cultivar, Williams 82, to fine-map the resistance genes. After inoculating similar to 200 F-2 individuals with either SMV (SC6-N) or BCMV (HZZB011), a segregation ratio of 3 resistant:1 susceptible was observed, indicating that for either virus, a single dominant gene confers resistance. Bulk segregation analysis (BSA) revealed that the BCMV-resistance gene is also linked to the SMV-resistance Rsv1 complex locus. Genotyping the F-2 individuals with 12 simple sequence repeat (SSR) markers across the Rsv1 complex locus then preliminarily mapped the SMV-resistance gene, Rsv1-r, between SSR markers BARCSOYSSR_13_1075 and BARCSOYSSR_13_1161 and the BCMV-resistance gene between BARCSOYSSR_13_1084 and BARCSOYSSR_13_1115. Furthermore, a population of 1009 F-2 individuals was screened with markers BARCSOYSSR_13_1075 and BARCSOYSSR_13_1161, and 32 recombinant F-2 individuals were identified. By determining the genotypes of these F-2 individuals on multiple internal SSR and single nucleotide polymorphism (SNP) markers and assaying the phenotypes of selected recombinant F-2:3 lines, both the SMV- and BCMV-resistance genes were fine-mapped to a common region (similar to 154.5 kb) between two SNP markers: SNP-38 and SNP-50. Within the mapped region, two CC-NBS-LRR genes exhibited significant divergence between Raiden and Williams 82, and their evolution has been affected by positive selection.