Camellia oleifera defatted-seed extract alleviates citrus postharvest decay by coordinating pathogen inhibition and host defense reprogramming

Postharvest fungal decay remains one of the major constraints limiting citrus storage and commercialization. Although plant-derived extracts have emerged as promising alternatives to synthetic fungicides, their biological mechanisms underlying postharvest protection remain poorly understood. Here, we investigated the postharvest preservation efficacy and underlying biological basis of Camellia oleifera Defatted-Seed Extract (CDSE) in citrus fruit through integrated physiological, microbiological, transcriptomic, and metabolomic analyses. CDSE treatment markedly reduced postharvest decay and delayed fruit softening without compromising fruit quality. In vitro and in vivo assays demonstrated that CDSE exhibited broad-spectrum antifungal activity against major citrus postharvest pathogens. Mechanistically, CDSE directly disrupted the plasma membrane integrity of Penicillium digitatum , resulting in severe hyphal damage and inhibited fungal growth. Meanwhile, CDSE maintained cell wall homeostasis by preserving lignin, cellulose, and protopectin contents while suppressing the activities and expression of cell wall-degrading enzymes. Transcriptome analysis further revealed that CDSE induced extensive defense-related transcriptional reprogramming, characterized by activation of plant–pathogen interaction pathways, phenylpropanoid biosynthesis, and immune-associated genes, including CERK , NPR , and multiple PR genes. Metabolomic profiling supported these transcriptional changes by demonstrating enhanced accumulation of phenolic acids, flavonoids, biogenic amines, and antioxidant-related metabolites involved in structural reinforcement and defense responses. Collectively, our results demonstrate that CDSE alleviates citrus postharvest decay through a dual mode of action by simultaneously suppressing pathogen growth and reinforcing host defense. This work reveals the biological basis underlying CDSE-mediated postharvest protection and provides a sustainable strategy for developing plant-derived preservatives to improve postharvest disease management and reduce food losses.