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) brings increasing losses in the cultivation of tobacco. 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 showed susceptibility (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°C. At a temperature above 28°C, all the cultivars showed mosaic discolorations or extensive necrosis. The reaction of the Nicotiana species was dependent on growth conditions. At 22°C, the reactions of sensitivity, tolerance and hypersensitivity to TMV were all observed, whereas above 28°C the species showed systemic necrotic symptoms. N. gossei was an exception because 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.