Increased Soybean Pubescence Density: Yield and Soybean mosaic virus Resistance Effects

Soybean mosaic virus (SMV) infection of double-cropped soybean [Glycine max (L.) Merr.] is likely to reduce yield due to soybean flowering date occurring after the start of aphid (Aphis spp.) movement that spreads the virus. Increased pubescence density provides a mechanical barrier to aphid probing that may delay SMV infection until after flowering, a strain-nonspecific resistance mechanism. The objectives of this study were to (i) evaluate the resistance benefit derived from increased pubescence density and the resulting reduction in incidence of SMV infection in soybean double-cropping systems, and (ii) compare the yield of soybean having increased pubescence density with the yield of genetically resistant genotypes of normal pubescence. Thirty soybean lines in three maturity sets with combinations of normal, dense, and extra-dense pubescence and SMV-resistant and -susceptible alleles were grown for 3 yr in late-planted tests at Lexington, KY. Inoculated border rows provided the virus source for natural aphid transmission of SMV. Extra-dense pubescence significantly reduced the incidence of SMV infection at R1 and R6 and produced a delay parameter on disease progress curves where the maximum disease increase was after flowering. In the late maturity set where the incidence of SMV infection on normal-pubescence SMV-susceptible genotypes was greater than 20%, extra-dense pubescence provided the same SMV resistance yield benefit as the Rsv₁^y resistance allele. The mean yield of extra-dense pubescence genotypes, however, was less than that of normal- and dense-pubescence genotypes.