Reactions of Commercial Soybean Cultivars from the Mid South to Soybean Mosaic Virus.

Soybean mosaic virus (SMV) is one of the most important viral diseases, causing drastic reductions in seed yield and quality. Seven SMV strains, G1 through G7, have been identified, and three resistance loci, Rsv1, Rsv3, and Rsv4, have been reported in the United States. The objectives of this study were to evaluate the reactions of a set of modern soybean [Glycine max (L.) Merr.] cultivars to SMV and to deduce which previously reported genes were involved in resistance. A total of 303 cultivars currently grown in the mid-southern United States were screened in the greenhouse with six SMV strains (G1, G2, G3, G5, G6, and G7). The results demonstrated that 189 cultivars were susceptible to all six SMV strains. Three cultivars were resistant to G1, G2, G3, G5, and G6 but developed stem-tip necrosis after infection with G7, so these were presumed to carry the Rsv1 allele. Sixty-six cultivars were resistant to G1 through G3 but susceptible to G5 through G7 and presumably carry Rsv1-y. One cultivar was resistant to G1 through G3 but necrotic to G5 through G7 and may carry Rsv1-k. Two cultivars probably carry Rsv1-t because they were resistant to G1, G2, G5, and G6 but necrotic to G3 and G7, and another two cultivars may carry Rsv1-n because they were necrotic to G1, G2, G5, and G6 but susceptible to G2 and G7. Four cultivars were susceptible to G1 through G3 but resistant to G5 through G7, and therefore they may carry Rsv3. Two cultivars were resistant to all six SMV strains, and therefore they may carry Rsv4, Rsv1-h, or two-gene combinations. There were 34 cultivars exhibiting unique SMV reaction patterns that may carry novel genes or alleles, including 23 cultivars that may carry novel alleles at the Rsv1 locus and 11 that may carry novel alleles at the Rsv3 locus. The results from this study can be used by breeders to choose resistant cultivars as parents in soybean breeding programs and by producers to select resistant cultivars in areas where SMV is a disease of concern for soybean production. [ABSTRACT FROM AUTHOR]