Anti-fungal activity of a novel succinate dehydrogenase inhibitor pydiflumetofen against Bipolaris maydis

Southern corn leaf blight (SCLB) is a disease caused by Bipolaris maydis. Pydiflumetofen is a novel succinate dehydrogenase inhibitor (SDHI) fungicide. However, its inhibitory activity against B. maydis has not been investigated in depth. In this study, mycelial growth rate and spore germination methods were used to establish a baseline for the sensitivity of 102 B. maydis strains collected from five regions of China to pydiflumetofen. The results showed that pydiflumetofen exhibited strong inhibitory activity against B. maydis. The EC50 values ranged from 0.0292 to 0.5207 mu g/mL and from 0.0115 to 0.4883 mu g/mL, with the average EC50 values of 0.2050 +/- 0.1779 mu g/mL and 0.1858 +/- 0.0994 mu g/mL for inhibition of mycelial growth and spore germination, respectively. After treatment with pydiflumetofen, the apical branching of mycelia increased significantly, and morphological changes such as twisting, deformation, rupture, and shriveling of mycelia and spores were observed. In addition, it significantly increased cell membrane permeability and decreased succinate dehydrogenase (SDH) activity and adenosine triphosphate (ATP) content. Moreover, the SDH gene expressions were changed, in which MbSdhB, MbSdhC and MbSdhD expressions were significantly upregulated, except for MbSdhA expression, which was significantly downregulated. In detached leaf experiments, pydiflumetofen showed strong protective and curative effects against B. maydis, superior to the same concentration of prochloraz and pyraclostrobin, and its protective effect was better than its curative effect. The field trials showed that the control efficacy of pydiflumetofen at 225 g/hm(2) was >70% and its control efficacy at 300 g/hm2 reached 81.77%, which was significantly higher than that of pyraclostrobin and epoxiconazole at the same dosage. After 1:1 mixing of pydiflumetofen with the above control agents, the control efficacies of these mixtures at the same dosage increased compared to the use of a single agent. All the above results demonstrated that pydiflumetofen exhibits excellent inhibitory activity against B. maydis and good control of SCLB, suggesting that it could be used as an alternative fungicide for the control of SCLB.