9-Methylstreptimidone: A novel promising fungicide disrupting material metabolism and energy synthesis in Colletotrichum orbiculare

Cucumber anthracnose caused by Colletotrichum orbiculare is one of the most critical diseases affecting cucurbit crops. Traditional chemical controls mitigate the disease but raise environmental and residue concerns, highlighting the need for eco-friendly alternatives. In this study, three glutarimide compounds were isolated from strain NEAU-S77, identified as a member of the genus Streptomyces, including the active compound 9-methylstreptimidone and two known analogs. 9-Methylstreptimidone exhibited strong antifungal activity against C. orbiculare, with an EC₅₀ of 1.09 μg/mL, outperforming the commercial fungicide Duofu (EC₅₀ = 4.12 μg/mL). Microscopic and biochemical analyses revealed that treatment with 9-methylstreptimidone caused abnormalities in mycelial and cellular structures, compromised cell wall integrity, and disrupted cellular redox equilibrium. Pot experiments showed higher control efficacy against cucumber anthracnose at 2 × and 4 × EC₅₀ (76.9 % and 87.6 %) than Duofu (70.2 % and 80.0 %). Transcriptomic analysis revealed that 9-methylstreptimidone predominantly interfered with the citrate cycle, oxidative phosphorylation, and peroxisome biogenesis. These findings elucidate the antifungal mechanism of 9-methylstreptomycin and underscore its potential as a sustainable fungicidal agent for managing cucumber anthracnose.