SOYBEAN MOSAIC-VIRUS RESISTANCE IMPROVES PRODUCTIVITY OF DOUBLE-CROPPED SOYBEAN

Double-cropped soybean [Glycine max (L.) Merr.], an important producti on system in the upper south and southeastern USA, has lower productiv ity 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 ear lier developmental stages when planted late than when planted early, t hus double-cropped soybeans may be more susceptible to yield reduction caused by SMV infection. The objectives of this study were to determi ne whether SMV resistance provided an average yield benefit in late pl anting and whether the expression of this benefit was dependent on bac kground genotypes. In 18 resistant/susceptible genotype pairs the resi stant genotypes, overall, provided 283 kg ha(-1) (12%) resistance bene fit for yield over susceptible genotypes in late plantings. This benef it 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 R-1 (r = 0.72, P < 0.01). In late planting environments resistance also provided benefits for se ed 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 produ ction system.