Efficacy of a novel succinate dehydrogenase inhibitor pydiflumetofen to control rice bakanae disease caused by Fusarium fujikuroi

Fusarium fujikuroi is the main pathogen causing rice bakanae disease. The fungicide pydiflumetofen is a novel succinate dehydrogenase inhibitor (SDHI). The activity of pydiflumetofen against F. fujikuroi and its efficacy of controlling rice bakanae disease is obscure. In this study, 100 strains of F. fujikuroi were isolated from different regions of Jiangsu and Zhejiang Province in China. The baseline sensitivity of F. fujikuroi to pydiflumetofen was established by mycelial growth assay and spore germination assay respectively, and physiological effect of the fungicide against F. fujikuroi and its control efficacy were investagated. The EC₅₀ (half effective concentration) values of pydiflumetofen on restraining mycelial growth against F. fujikuroi population (n = 100) ranged from 0.0125 μg/mL to 0.1118 μg/mL and the mean value was 0.0503 (± 0.0029) μg/mL. The EC₅₀ values of pydiflumetofen on inhibiting spore germination distributed from 0.0001 μg/mL to 0.0245 μg/mL and the mean value was 0.0038 (± 0.0005) μg/mL. Treated with 0.05 μg/mL (EC₅₀ value) or 1.3 μg/mL (EC₉₀ value) pydiflumetofen, the offshoot of top mycelia of F. fujikuroi increased while sporulation production descreased. The membrane structure and organelles (eg. mitochondria) were damaged and the intracellular plasma leakage increased through imperfect membrane. There was no significant difference in the exopolysaccharides production while peroxidase activity declined after treated with pydiflumetofen. Control efficacy of 10, 15 and 20 g a.i./100 kg seeds of pydiflumetofen against rice bakanae disease by seed dressing is 94.77%, 98.60 % and 100% respectively. Above results indicate that pydiflumetofen has very high activity against F. fujikuroi and is a nice fungicide for controlling rice bakanae disease caused by F. fujikuroi.