Isolation of a cultivar-specific gene to soybean stunt virus

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Host resistance to plant viruses is specifically observed depending on host-virus combination. Using Cucumber mosaic virus(CMV) and its soybean starain (SSV), we analyzed the resistant phenotype that a virus does not systemicaily spread but it it is localized in the inoculated leaves in two host-virus combinations (host species-CMVs and soybean cultivars-SSVs). In the latter combination, we determined where the resistance mechanism operates and suggested existence of two complementary dominant host factors to control the sobybean cultivar resistance to SSV. Both in cucumber-CMV and in soybean-SSV combinations, the primary determinant for systemic infection is the domain including the 3a gene and depending on cultivars, an additional viral gene (the CP gene) was required in the cultivar resistance to SSV, the S region of RNA3 (mainly the 5' non-translated region) and the region including the entire 2b gene were together necessary for the systemic movement. It is therefore consistant with the observation that there are two host factors to affect the viral sysmtemic infection.