Pyridaben as a Novel Fungicide Against <i>Sphaerotheca fuliginea</i>, the Causal Agent of Cucumber Powdery Mildew

Pyridaben is a novel broad-spectrum insecticide and acaricide that is effective against thrips, mites, aphids, and leafhoppers. We accidentally discovered that pyridaben was able to prevent cucumber powdery mildew. In this study, we explored the inhibitory effects and underlying mechanisms of pyridaben against <i>Sphaerotheca fuliginea</i>. Pyridaben effectively inhibited the spore germination and mycelial growth of <i>S. fuliginea</i> with half-maximal inhibitory concentration (IC₅₀) of 10.83 mg/liter and 18.28 mg/liter, respectively. The spore germination, mycelial growth, and secondary spore formation of <i>S. fuliginea</i> was severely hindered on cucumber leaves treated with pyridaben at 20 mg/liter. Scanning electron microscopy revealed that the mycelia growing on pyridaben-treated cucumber leaves were much finer than those growing on untreated leaves. Transcriptomic analysis revealed that pyridaben had a significant impact on the ribosomal function and energy metabolism of the powdery mildew pathogen, restricting its normal physiological activities. In field experiments, the efficacies of pyridaben reached 76.48% in Zhejiang Province and 78.40% in Shandong Province at the rate of 225 g a.i./ha after two applications, which were comparable to the commercialized fungicides. These results suggest pyridaben is not only an insecticide but also an effective fungicide with the potential for further application in preventing and controlling cucumber powdery mildew.