Resistance risk, resistance mechanism and the effect on DON production of a new SDHI fungicide cyclobutrifluram in Fusarium graminearum.

Fusarium head blight in wheat is caused by Fusarium graminearum, resulting in significant yield losses and grain contamination with deoxynivalenol (DON), which poses a potential threat to animal health. Cyclobutrifluram, a newly developed succinate dehydrogenase inhibitor, has shown excellent inhibition of Fusarium spp. However, the resistance risk of F. graminearum to cyclobutrifluram and the molecular mechanism of resistance have not been determined. In this study, we established the average EC of a range of F. graminearum isolates to cyclobutrifluram to be 0.0110 μg/mL. Six cyclobutrifluram-resistant mutants were obtained using fungicide adaptation. All mutants exhibited impaired fitness relative to their parental isolates. This was evident from measurements of mycelial growth, conidiation, conidial germination, virulence, and DON production. Interestingly, cyclobutrifluram did not seem to affect the DON production of either the sensitive isolates or the resistant mutants. Furthermore, a positive cross-resistance was observed between cyclobutrifluram and pydiflumetofen. These findings suggest that F. graminearum carries a moderate to high risk of developing resistance to cyclobutrifluram. Additionally, point mutations H248Y in FgSdhB and A73V in FgSdhC of F. graminearum were observed in the cyclobutrifluram-resistant mutants. Finally, an overexpression transformation assay and molecular docking indicated that FgSdhB or FgSdhC could confer resistance of F. graminearum to cyclobutrifluram.