Multi-Target Antifungal Mechanism of Vapor-Phase Cymbopogon citratus Essential Oil: Effective Control of Postharvest Botrytis cinerea and Powdery Mildew

Botrytis cinerea poses severe postharvest losses in horticultural products, while synthetic fungicides raise food safety concerns. This study developed a GRAS-compliant antifungal strategy using vapor-phase Cymbopogon citratus essential oil (EO). GC-MS revealed citronellal (17.06%) as the dominant bioactive compound. The EO exhibited superior vapor-phase activity against B. cinerea, with EC50 of 14.69 µg/mL (mycelial growth) and MIC of 7.81 µg/mL (spore germination), significantly lower than direct-contact efficacy (p < 0.05). Mechanistic analysis revealed a tripartite mode of action—rapid membrane disintegration (48% electrolyte leakage within 4 h), suppression of ROS defense enzymes (SOD/CAT/POD inhibition > 50%), and disruption of mitochondrial energetics (SDH activity reduced by 58.1%)—which induced irreversible cellular collapse. This multi-target strategy mitigates resistance development, a key limitation of single-mode fungicides. In commercial-scale trials, EO fumigation (125 µg/mL) reduced cherry tomato decay by 81.9–92.6% during 28-day storage, while maintaining firmness (15.9% higher than control) and nutritional quality (titratable acidity (TA) and total sugar content (TSC)). Notably, the vapor-phase EO also exhibited potent inhibitory activity against the spore germination of rubber tree powdery mildew (EC50: 3.19 µg/mL), demonstrating its broad-spectrum antifungal potential. This finding significantly expands the application scope of C. citratus EO from postharvest preservation to preharvest crop protection. This work provides a scalable, residue-free alternative to synthetic fungicides for industrial postharvest applications.