Antifungal Mechanism of Biphenyl Phytoalexin Derivative Sorbauphylin A against <i>Botrytis cinerea</i> in Grapes

<i>Botrytis cinerea</i> causes significant losses in crops, especially in grapes. The biphenyl derivative sorbauphylin A (4'-<i>n</i>-pentyl-[1,1'-biphenyl]-3,5-diol), derived from plant phytoalexins, exerts potent antifungal effects with low toxicity. This study demonstrated that sorbauphylin A significantly inhibited the growth of <i>B. cinerea</i> (EC₅₀ = 15 μg mL^-1), suppressed spore germination, and markedly reduced infection in grapes and leaves. The results of fluorescence staining and enzyme activity detection indicated that sorbauphylin A damaged cell membranes and walls and triggered a reactive oxygen species burst. Transcriptome analysis revealed that sorbauphylin A inhibited the thiamine biosynthesis pathway by downregulating key genes <i>Bcthi4</i> and <i>Bcnmt1</i>, which molecular docking confirmed, thereby reducing thiamine pyrophosphate (TPP) production. This suppression of TPP disrupted pyruvate metabolism and the tricarboxylic acid cycle, leading to mitochondrial energy deficiency and consequently inducing oxidative stress and fungal cell death. Sorbauphylin A represents a promising new fungicide for controlling grape gray molds with broad application prospects.