Allelomorphic Relationship Between Rsv1-y in Cultivar York and Rsv1 In PI 96983 for Resistance to Soybean Mosaic Virus.

Soybean mosaic virus (SMV) is one of most destructive soybean viral diseases, and causes significant seed yield and seed quality reduction. All SMV isolates in the U.S. were classified in seven strain groups (G1 to G7). Three SMV resistance loci, Rsv1, Rsv3, and Rsv4 have been reported so far; each locus contains two or more alleles that confer different SMV reaction patterns. Rsv1 was the first locus identified in PI 96983 conferring resistance to G1 through G6 and necrosis to G7. Rsv1-y is one of nine Rsv1 alleles and confers resistance to G1 through G3, necrosis to G4, but susceptibility to G5 through G7. In a previous molecular screen, a nearly perfect marker at the Rsv1 locus amplified all the known Rsv1 alleles, but not Rsv1-y in York, raising a question of whether Rsv1-y belongs to a different but tightly linked locus. This study was undertaken to re-evaluate the allelomorphic relationship between the Rsv1-y allele and the Rsv1 locus. York was crossed with PI 96983 and 971 F_2:3 lines from PI 96983 x York were screened with G1. The SSR marker SOYBRAR 1133-33 was used to genotype the F₂ population from the same cross. Tissue blotting immunosorbent assay was used to confirm the presence of the virus in the infected plants. The results showed that Rsv1 and Rsv1-y are two closely linked genes that are 0.5 cM apart. We propose that the symbol Rsv2 be assigned to York to replace Rsv1-y.