Soybean mosaic virus resistance improves productivity of double-cropped soybean

Double-cropped soybean [Glycine max (L.) Merr.], an important production system in the upper south and southeastern USA, has lower productivity than full season soybean. Soybean mosaic virus (SMV) appears to be prevalent in soybean in the upper south of the USA. Yield losses due to SMV infection are greater the earlier infection occurs in relation to soybean developmental stages. Soybean may be infected by SMV at earlier developmental stages when planted late than when planted early, thus double-cropped soybeans my be more susceptible to yield reduction caused by SMV infection. The objectives of this study were to determine whether SMV resistance provided an average yield benefit in late planting and whether the expression of this benefit was dependent on background genotypes. In 18 resistant/susceptible genotype pairs the resistant genotypes, overall, provided 283 kg ha^-1 (12%) resistance benefit for yield over susceptible genotypes in late plantings. This benefit was independent of background genotype and significantly correlated with the difference between early plantings and late plantings in the incidence of SMV infection at growth stage R₁ (r = 0.72, P < 0.01). In late planting environments resistance also provided benefits for seed quality traits, i.e, no seed transmission of SMV and low seed coat mottling. We recommend that resistance to SMV should be incorporated into soybean cultivars which will be used in the double-cropping production system.