Identification, anastomosis grouping and pathogenicity analyses of tobacco target spot pathogen in Hunan

To clarify the species and pathogenicity of tobacco target spot pathogen and the resistance of tobacco cultivars to this disease, pathogens from tobacco leaves suspected of being infected with target spot in Hunan tobacco-growing areas were isolated and cultured, and morphological and molecular identifications were conducted. Meanwhile, the slide confrontation method was employed for anastomosis grouping analysis. The pathogenicity of strains was determined with disease index as the resistance evaluation index and the resistance and susceptibility of 11 tobacco cultivars were identified with average diameter(AD)of spots as the criterion. The results showed that all 36 isolated pathogens were Rhizoctonia solani AG3. Pathogenicity differentiation existed among the pathogens. Strains with intermediate pathogenicity were the dominant group, and strains from different geographical sources displayed varying pathogenicity. All 11 main tobacco cultivars showed high susceptibility to tobacco target spots, and there were differences in spot diameters among different infected cultivars.