Characterization of Mating Types, Genetic Diversity, Pathogenicity, and Sensitivity to Tebuconazole in Bipolaris maydis Isolates from Henan Province, China

To clarify mating type distribution, genetic structure, and sensitivity to tebuconazole in Bipolaris maydis (Nisikado et Miyake) Shoem from Henan Province, 146 isolates were assessed for mating type using multiplex PCR， and their genetic diversity was analyzed using ISSR markers. Pathogenicity of 107 isolates on resistant and susceptible maize cultivars was evaluated by field inoculation. The sensitivity of 167 isolates to tebuconazole was determined using the mycelial growth rate method. The ratio of MAT1-1 to MAT1-2 isolates was 1.15：1, which conformed to the theoretical 1：1 expectation (χ² = 0.6849, P = 0.41) with no significant deviation. These populations exhibited a high level of genetic diversity (polymorphic loci, PPL = 98.7%). All geographical populations were closely related (genetic similarity coefficient, GS > 0.94) but displayed discernible phylogenetic differences; northern Henan and eastern Henan populations were the most closely related, whereas the Jiangsu and Shandong populations were the most distantly related. All isolates infected both resistant and susceptible maize cultivars, with disease indices from 33.33 to 100.00. Pathogenicity of regional isolates differed obviously. The EC 50 values of tebuconazole for the 167 isolates ranged from 0.0191 to 1.0411 μg·mL⁻¹, with a mean of 0.3665 ± 0.2254 μg·mL⁻¹. The frequency distribution of sensitivity showed a unimodal curve, establishing a baseline sensitivity of B. maydis to tebuconazole. This study elucidates the population genetic structure and pathogenic differentiation of B. maydis and provides a baseline sensitivity to tebuconazole, which provides a theoretical basis for integrated disease management.