Resistance risk assessment for Fusarium graminearum to pydiflumetofen, a new succinate dehydrogenase inhibitor

Background Pydiflumetofen is a new generation succinate dehydrogenase inhibitor currently undergoing the process of registration in China for the control of Fusarium head blight in wheat. A resistance risk assessment of Fusarium graminearum to pydiflumetofen was undertaken in this study. Results A total of 75 pydiflumetofen-resistant mutants were generated through spontaneous selection and displayed high resistance with an average resistance factor (RF) value of 78. Four mutants were generated through UV mutagenesis and displayed very high resistance with an RF value >1000. The sequence analysis results for Sdh genes and fitness studies revealed the existence of four types of mutations. In particular, 32 spontaneous selection mutants (SP mutants) had an arginine (R) to histidine (H) transition at position 86 in FGSdhC, resulting in seriously reduced fitness. Seven SP mutants had an R to cysteine (C) transition at position 86 in FGSdhC, resulting in reduced fitness. Thirty-six SP mutants had an alanine (A) to valine (V) transition at position 83 in FGSdhC and had no fitness penalties. The efficacy of pydiflumetofen towards a mutant carrying A83V in FGSdhC in vivo was significantly decreased at 42.7%. Four UV mutants had no mutations on all Sdh genes and no fitness penalties. Cross-resistance among boscalid, fluopyram and pydiflumetofen was observed. Conclusion Sdhc mutations were found and other target site resistance may be present in laboratory PR mutants of F. graminearum. An overall moderate risk of resistance development in F. graminearum was recommended for pydiflumetofen. (c) 2019 Society of Chemical Industry