1Department of Virology, DLO Research Institute for Plant Protection (IPO-DLO), P. O. Box 9060, 6700 GW Wageningen, The Netherlands; 2Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843, U.S.A.; 3Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, U.S.A.
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Accepted 28 October 2000.
A viral genetic system was used to map the determinants of the ability of Tomato spotted wilt virus (TSWV) to overcome the R gene (Sw-5) in tomato and the resistance conferred by the nucleocapsid gene of TSWV (N gene) in tobacco. A complete set of reassortant genotypes was generated from TSWV isolates A and D. TSWV-A was able to overcome the Sw-5 gene in tomato and the TSWV N gene in tobacco, whereas TSWV-D was repressed by both forms of resistance. The ability to overcome both forms of resistance was associated with the M RNA segment of TSWV-A (MA). Overcoming the Sw-5 gene was linked solely to the presence of MA, to overcome the TSWV N gene was modified by the L RNA and the S RNA of TSWV-A, which is consistent with previous reports that suggest that the nucleocapsid gene is not the primary determinant for overcoming the nucleocapsid-mediated resistance. Sequence analysis of the M RNA segment of TSWV-A, -D, and the type isolate BR-01 revealed multiple differences in the coding and noncoding regions, which prevented identification of the resistance-breaking nucleotide sequences.
© 2001 The American Phytopathological Society