In Vitro Determination of the Sensitivity of Fusarium graminearum to Fungicide Fluopyram and Investigation of the Resistance Mechanism

Fusarium head blight (FHB), caused by Fusarium graminearum, is a significant disease of wheat. In this study, the sensitivity of 102 F. graminearum isolates to fluopyram was determined based on inhibition of conidia germination and mycelial growth. The EC50 value ranged from 0.0952 to 0.2717 μg/mL and1.0326 to 4.8512 μg/mL, with the mean EC50 value of 0.1631 ± 0.0383 and 2.5638 ± 0.7500 μg/mL, respectively. The resistance of the fluopyram-resistant mutants could be stably inherited, and the survival fitness of the mutants was higher than that of the parental isolates. Positive cross-resistance was observed between fluopyram and pydiflumetofen, but no cross-resistance was observed between fluopyram and epoxiconazole, phenamacril, metconazole, carbendazim, or fludioxonil. Amino acid substitution A73 V was detected on the FgSDHC1 subunit, and the FgSdhC1 gene was significantly upregulated after exposure to fluopyram. These results indicate that fluopyram exerts its inhibitory activity by targeting the FgSdhC1 gene of F. graminearum.