Two Tightly Linked Genes for Soybean Mosaic Virus Resistance in Soybean.

Soybean mosaic virus (SMV), a member of the Potyviridae family, is the most common virus negatively affecting yield and seed quality in soybean [Glycine max (L.) Merr.]. Seven SMV strains, G1 through G7, and three independent SMV resistance genes (R-genes), Rsv1, Rsv3, and Rsv4, have been previously identified. The Rsv1 locus contains at least 10 alleles conferring differential plant reactions to SMV strains, and it was mapped at very complex resistancegene-rich region. In this study, two alleles of the Rsv1 locus were analyzed by crossing PI 96983 (Rsv1) and cultivar York (Rsv1-y) soybean to evaluate whether Rsv1 and Rsv1-y belong to the same or different but closely linked loci. To break possible linkage, 3000 F2:3 lines were developed and investigated using infections of the SMVG1 strain in a greenhouse. The occurrence of segregating and susceptible lines indicated tight linkage between two genes. The recombination frequency (RF) was estimated using the maximum likelihood (ML) formula concluding that Rsv1 and Rsv1-y are two tightly linked loci located apart with genetic distance of 2.2 cM on chromosome 13. A new symbol of Rsv5 has been assigned for the resistance gene in York to replace the original Rsv1-y allele assignment. This research provided the first evidence for existence of two R-genes on chromosome 13, conferring resistance to different SMV strains. Both loci, Rsv1 and Rsv5, can be easily transferred into susceptible cultivars in a breeding program to provide broad and durable protection against SMV strains. [ABSTRACT FROM AUTHOR]