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.