Identification of a New Allele at the Rsv3 Locus for Resistance to Soybean Mosaic Virus in PI 61944 Soybean Accession

Soybean mosaic virus (SMV) is a prevalent pathogen in soybean [Glycine max, (L.) Merr.]. Several SMV resistance genes have been discovered, but most of them do not provide resistance to all strains of SMV. The objective of this research was to identify new genes or alleles displaying differential reactions to SMV strains in the SMV-resistant soybean genotype, PI 61944. Cross combinations were made to develop F-2 and F-2:3 populations, followed by mapping analyses and greenhouse screenings using G1 and G7 virus strains. A resistant parent, PI 61944 (Rsv-?), was crossed with a susceptible parent, Essex (rsv), and with differential parents, PI 96983 (Rsv1), L29 (Rsv3), V94-5152 (Rsv4), and PI 507389 (Rsv1-n), for allelism tests. Results indicated that resistance to SMV in PI 61944 was controlled by a single, dominant gene. This gene did not appear to be allelic to the Rsv1 locus as was previously reported. Allelism test revealed that the resistance allele in PI 61944 is located at the Rsv3 locus. A molecular marker analysis further revealed that the resistance allele in PI 61944 is located at linkage group B2 (chromosome 14). Additionally, PI 61944 exhibited unique SMV reaction patterns when compared with the reported Rsv3 allele in L29. Therefore, we propose that the new allele, Rsv3-n, be assigned to the SMV resistance locus in PI 61944. The Rsv3 alleles are rare to find among the soybean germplasm, but can confer resistance to aggressive SMV strains; therefore, we expect PI 61944 to be useful in future breeding efforts.