Study on Mechanisms of Resistance to SDHI Fungicide Pydiflumetofen in .

Rice bakaenii disease (RBD) is a widespread and devastating disease mainly caused by . Pydiflumetofen (Pyd) is a novel succinate dehydrogenase inhibitor (SDHI) with strong inhibitory activity against , but the mechanism of resistance to Pyd has not been well studied for this pathogen. Through fungicide adaption, a total of 12 Pyd-resistant mutants were obtained and the resistance level could be divided into three categories of high resistance (HR), moderate resistance (MR), and low resistance (LR) with resistance factors (RF) of 184.04-672.90, 12.63-42.49, and <10, respectively. Seven genotypes of point mutations in genes (FfSdhB, FfSdhB, FfSdhB, FfSdhC, FfSdhC, FfSdhD, and FfSdhD) were found in these mutants, among which genotype FfSdhB and FfSdhC mutants showed HR, genotype FfSdhB, FfSdhB, FfSdhC, and FfSdhD mutants showed MR, and genotype FfSdhD mutants showed LR. Moreover, all the substitutions of amino acid point mutations including FfSdhB, FfSdhC, and FfSdhD conferring resistance to Pyd in were verified by protoplast transformation. Additionally, a positive cross-resistance was detected between Pyd and another SDHI fungicide penflufen, while no cross-resistance was detected between Pyd and phenamacril, prochloraz, azoxystrobin, carbendazim, or fludioxonil. Although pathogenicity of the mutants was increased compared with that of the wild-type parental strains, the mycelial growth rate and spore production levels of the resistant mutants were significantly decreased ( < 0.05), indicating significant fitness cost of resistance to Pyd in . Taken together, the risk of resistance to Pyd in might be moderate, and appropriate precautions against resistance development in natural populations should be taken into account when Pyd is used for the control of RBD.