Nature of Resistance of a Tobacco Cultivar to Tobacco Vein Mottling Virus. Karen S. Gibb. Department of Plant Pathology, University of Kentucky, Lexington 40546 U.S.A. Gary M. Hellmann, and Thomas P. Pirone. Department of Plant Pathology, University of Kentucky, Lexington 40546 U.S.A. MPMI 2:332-339. Accepted 7 July 1989. Copyright 1989 The American Phytopathological Society.

Comparative studies were done on the reaction of a “resistant” (Tennessee 86) cultivar and a susceptible (Kentucky 14) cultivar of tobacco to tobacco vein mottling virus (TVMV). In Tennessee 86 (Tn 86), TVMV did not spread to uninoculated leaves but could be recovered from inoculated leaves as determined by infectivity assay. In tests to determine the extent of virus spread, cylindrical inclusion (CI) protein and coat protein (CP) could be detected by immunostaining strips of epidermal cells taken from inoculated Kentucky 14 (Ky 14) leaves as early as 5 days postinoculation, and by 15 days numerous epidermal cells were stained. In the epidermis of Tn 86, CI and CP were confined to a few isolated cells or groups of cells for at least 15 days postinoculation. CI was detected in Ky 14 mesophyll cells within 5 days after mechanical inoculation but was not detected in Tn 86 mesophyll cells up to 15 days postinoculation. The spread and distribution in Tn 86 of TVMV-S, an isolate of TVMV which infects Tn 86 systemically, were similar to that of TVMV in Ky 14. Electroporated protoplasts from both Ky 14 and Tn 86 supported the accumulation of TVMV, although the final amount of virus accumulated was lower in the Tn 86 protoplasts. The results suggest that resistance of Tn 86 is primarily due to restricted virus movement, although a reduction in the number of initial infection sites and in the rate of virus accumulation may also play a role.