Resistance risk assessment for a novel succinate dehydrogenase inhibitor pydiflumetofen in Fusarium asiaticum

Abstract BACKGROUND Fusarium asiaticum is one of predominant pathogens of Fusarium head blight (FHB) in China. Pydiflumetofen (Pyd) is a novel succinate dehydrogenase inhibitor (SDHI) which has been commercialized in China for the controlling of wheat FHB since 2019. In the current study, a risk assessment of the pydiflumetofen‐resistance selected in Fusarium asiaticum was investigated. RESULTS One Pyd MR mutant [resistance factor (RF) < 80] and four Pyd HR mutants (RF > 3000) were generated by fungicide‐taming from 1000 mycelial discs of the wild‐type strain 2021. Nucleotide sequences alignment results of FaSdh from the wild‐type strain and resistant mutants showed that all the mutations were categorized into three genotypes, i.e. FaSdhB H248Y from Pyd MR mutant, both FaSdhC 1 A64V and FaSdhC 1 R67K from Pyd HR mutants. All the resistant mutants possessed no fitness penalty based on the data of mycelial linear growth, conidiation and virulence. In addition, the FaSdhC 1 A64V mutants showed positive cross‐resistance between pydiflumetofen and boscalid or thifluzamide, but no cross‐resistance between pydiflumetofen and Y13149 or Y12196, while the FaSdhC 1 R67K mutants exhibited positive cross‐resistance between pydiflumetofen and boscalid, thifluzamide or Y12196, and no cross‐resistance between pydiflumetofen and Y13149. Furthermore, positive cross‐resistance between the five tested SDHIs was detected in the FaSdhB H248Y mutants. CONCLUSION The results suggest a moderate to high resistance risk of F. asiaticum to pydiflumetofen, and provide essential data for monitoring the emergence of resistance and resistance management strategies for pydiflumetofen, which will be useful for scientific application of this fungicide in China.