Rsv1-mediated resistance against Soybean mosaic virus-N is hypersensitive response-independent at inoculation site, but has the potential to initiatea hypersensitive response-like mechanism

Rsv1, a single dominant gene in soybean PI 96983, confers resistance to mos t strains of Soybean mosaic virus (SMV), including strain G2. The phenotypi c response includes the lack of symptoms and virus recovery from mechanical ly inoculated leaves. To study the resistance mechanism, SMV-N (an isolate of strain G2) was introduced into PI 96983 by grafting. Hypersensitive resp onse (HR)-like lesions occurred on the stems, petioles, and leaf veins, and virus was recovered from these lesions, The response demonstrated the cyto logical and histological characteristics of HR as well as elevated transcri ption of a soybean salicylic acid-inducible, pathogenesis-related (PR-1) pr otein gene. Mechanical inoculation of PI 96983 primary leaves with a high l evel of SMV-N virions caused no symptoms or up regulation of the PR-1 prote in gene transcript. Furthermore, inoculation with infectious viral RNA did not alter the resistance phenotype. The data suggest that interaction of SM V-N with Rsv1 has the potential to induce an HR-like defense reaction, Rsv1 -mediated resistance in the inoculated leaf, however, is HR-independent and operates after virion disassembly.