LAUSR

BACKGROUND Fusarium head blight (FHB) caused by Fusarium graminearum complex (Fg) is a devastating disease of cereal crops worldwide. The succinate dehydrogenase inhibitor (SDHI), pydiflumetofen, has been registered for management of FHB in China in 2019. Previously, laboratory induced pydiflumetofen-resistant (PyR) mutants of Fg have been characterized. However, resistance situation of Fg to pydiflumetofen in the field remains largely unknown. RESULTS After screening 6468 isolates of Fg from various regions of China, six PyR isolates were identified. All six resistant isolates exhibited no fitness penalties based on mycelial growth, conidiation and virulence. However, no cross-resistance between pydiflumetofen and azoxystrobin, tebuconazole or fludioxonil in Fg was detected. Genome-seq revealed that all six PyR isolates contained a point mutation A78V in FgSdhC1 (FgSdhC1A78V ). Genetic replacement assay further confirmed that FgSdhC1A78V conferred resistance of Fg to pydiflumetofen. Based on this, a mismatch allele-specific polymerase chain reaction (MAS-PCR) was developed for rapidly detecting the PyR isolates containing the FgSdhC1A78V mutation in Fg. CONCLUSION This is the first time that resistance of Fg to pydiflumetofen in the field was reported and point mutation FgSdhC1A78V conferring resistance of Fg to pydiflumetofen was confirmed. This study provides critical information for monitoring and managing pydiflumetofen resistance in Fg.