Soybean mosaic virus (SMV) is distributed worldwide. The primary mode of transmission is through seed (Goodman and Oard, 1980), although the virus is also nonpersistently transmitted by aphids (Irwin and Goodman, 1981). Cul-tivars have been identified which combine tolerance to SMV infection and low incidence of transmission through seed (Goodman and Oard, 1980).