Strains of Soybean Mosaic Virus: Classification Based on Virulence in Resistant Soybean Cultivars

Abstract

Isolates (98) of soybean mosaic virus (SMV) from seeds in the USDA [United States Department of Agriculture] soybean germ plasm collections were classified into 7 strains based on disease reactions of inoculated differential soybean cultivars. Two susceptible soybean cultivars (Clark and Rampage) and 6 putatively resistant cultivars (Buffalo, Davis, Kwanggyo, Marshall, Ogden and York) were used. The results showed differences in virulence among SMV strains and in the susceptibility and reactions of soybean cultivars to these strains. Cultivars resistant to less virulent strains in most cases exhibited severe necrotic symptoms when inoculated with more virulent strains. All SMV strains tested caused infection and typical mosaic symptoms in cultivars Clark and Rampage. Strain G1 (including ATCC PV-94) did not infect any of the resistant cultivars. Strain G2 caused local and systemic necrosis in ''Marshall'' but did not infect other resistant cultivars. Strain G3 and strain G4 caused local and systemic necrosis in both ''Ogden'' and ''Marshall''; strain G4 also infected ''Davis'' and ''York'', causing either local and systemic necrosis or mosaic symptoms. Strains G5, G6 and G7 caused mosaic symptoms in ''Davis'' and ''York''; strain G5 also caused necrosis in ''Kwanggyo'', strain G6 caused necrosis in both ''Kwanggyo'' and ''Marshall'', and strain G7, which infected all cultivars tested, caused necrosis in ''Marshall'', ''Odgen'', ''Kwanggyo'' and ''Buffalo''. The incidence of SMV and the presence of highly virulent strains in germplasm collections call for use of a range of SMV strains in soybean breeding programs in which SMV resistance is an objective.