Citrus-leaf microemulsion controls postharvest mold through membrane disruption and host defense enhancement

Postharvest fungal decay causes substantial losses in the global citrus industry. To address fungicide resistance and waste management, this study developed a circular “from-tree-to-fruit” strategy, valorizing citrus leaf residues into a stable 7% microemulsion (7% ME). Optimized extraction yielded a Citrus Leaf Extract (CLE) enriched with the antifungal 2,4-di-tert-butylphenol (2,4-DTBP). At 5 × EC 50 , 7% ME controlled blue mold ( Penicillium italicum ) and green mold ( P. digitatum ) by 77.4% and 94.5%, respectively, compared with 71.0% and 81.3% for thiabendazole. Mechanistic analyses revealed a dual mode of action: direct disruption of fungal membrane integrity and induction of key host defense enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), thereby enhancing the fruit's innate resistance. Furthermore, ecotoxicological assessments confirmed the safety of the 7% ME for non-target organisms, including silkworms, zebrafish, and earthworms. This study presents a scalable, eco-friendly framework for transforming agricultural byproducts into high-performance biopesticides.