Reaction of Nicotiana Species and Cultivars of Tobacco to Tobacco mosaic virus and Detection of the N Gene that Confers Hypersensitive Resistance

Tobacco mosaic virus (TMV) causes large losses in tobacco cultivation. Sixty-two cultivars of tobacco and eleven species of Nicotiana were evaluated for resistance to TMV. Biological tests at two temperature ranges, DAS-ELISA and molecular markers were applied to assess the resistance to TMV. Most cultivars of tobacco were susceptible (S) to TMV, two were tolerant (T), while others revealed a hypersensitive response (HR). Hypersensitivity, determined by the N gene, occurred only at a temperature below 22 degrees C. At a temperature above 28 degrees C, all the cultivars showed mosaic discolorations or extensive necrosis. The reaction of the Nicotiana species was dependent on growth conditions. At 22 degrees C, the reactions of susceptibility, tolerance and hypersensitivity to TMV were all observed, whereas above 28 degrees C the species showed systemic necrotic symptoms. N. gossei was an exception in that hypersensitivity occurred regardless of the thermal conditions. The resistance of this species was not conditioned by the N gene, which suggests that N. gossei could be an additional genetic resource for tobacco breeding.