Discovery of (+)-Methyl Nonactate as a Potential Fungicide against Gummy Stem Blight.

Gummy stem blight (GSB), which is caused by , threatens pumpkin yields and agriculture. Effective, safe antifungal agents are urgently needed. In this study, fermentation broth supernatant of sp. NEAU-T55 demonstrated considerable antifungal activity against . Activity-guided isolation identified 2 new and 14 known compounds, with (+)-methyl nonactate () determined as the main active ingredient. This compound exhibited strong antifungal activity (EC = 0.12 μg mL), outperforming difenoconazole (EC = 0.17 μg mL), and achieved 74.1% control efficacy in the pot experiments. Microscopy revealed that (+)-methyl nonactate impeded mycelial growth and induced morphological alterations. Transcriptomic analysis indicated that (+)-methyl nonactate may inhibit acetolactate synthase, thereby disrupting amino acid metabolism and diminishing precursor availability for the tricarboxylic acid cycle. This research represents the first application of (+)-methyl nonactate for GSB control and provides insights into its antifungal mechanisms, laying the groundwork for its potential development as a novel agricultural antibiotic.