Molecular and Biochemical Characterization of Pydiflumetofen-Resistant Mutants of .

Gummy stem blight (GSB), caused by , is a devastating disease on watermelon. Pydiflumetofen belongs to succinate dehydrogenase inhibitor (SDHI) fungicide, which is effective in controlling many plant diseases. The EC values of 69 isolates to pydiflumetofen ranged from 0.0018 to 0.0071 μg/mL, and the minimal inhibitory concentration (MIC) value of all strains to pydiflumetofen was <0.05 μg/mL. Eight pydiflumetofen-resistant mutants were obtained, and the level of resistance was stable. The mycelial growth, dry weight of mycelia, hyphal morphology, and pathogenicity of most resistant mutants did not change significantly compared with their parental strains, which indicated that the resistance risk of to pydiflumetofen would be medium to high. Sequencing alignment showed that five resistant mutants presented a mutation at codon 277 (H277Y) in the gene. The point mutants exhibited decreased sensitivity to pydiflumetofen in , which indicated that the point mutants of could reduce sensitivity to pydiflumetofen. These results further increase our understanding about the mode of action and the resistance mechanism of pydiflumetofen.