Disrupting cytomembrane function mediates the antifungal activity of carvacrol against Sclerotium rolfsii.

Peanut stem rot (PSR), caused by the fungus Sclerotium rolfsii, is a devastating plant disease that causes severe yield losses and substantial economic impacts in agriculture worldwide. Carvacrol, a natural compound with broad-spectrum antifungal properties, shows significant inhibitory effects on various pathogens. In this study, carvacrol and nano-carvacrol demonstrated strong antifungal activity against S. rolfsii, with 50 % effective concentration (EC50) values of 39.46 mg/L and 19.20 mg/L, respectively. Carvacrol and nano-carvacrol can reduce mycelial growth and suppress the formation and germination of sclerotia. Scanning and transmission electron microscopy revealed carvacrol-induced mycelial deformation and ultrastructural damage. Carvacrol also increases membrane permeability, leading to cell death. Transcriptome analysis with GO/KEGG enrichment revealed that carvacrol disrupted cell membrane biosynthesis, inhibited ergosterol biosynthesis, and interfered with the endoplasmic reticulum pathway. The results of propidium iodide staining of fungal mycelium treated with carvacrol exhibited pronounced PI fluorescence, indicating a general loss of membrane integrity, complete loss of viability, and irreversible membrane damage. qPCR results revealed downregulation of key genes involved in ergosterol biosynthesis and those of cytochrome P450. Both greenhouse and field trials have confirmed that carvacrol and nano-carvacrol have a high control efficacy against PSR, with protective effects superior to those of curative treatments. These findings highlight carvacrol's potential as an eco-friendly fungicide with a novel mode of action.