https://doi.org/10.37229/fsa.fja.2026.10.12

This study evaluated the postharvest application of salicylic acid (SA; 4, 8, and 16 mM) and chitosan (CS; 12.4, 31, and 62 mM) for controlling green mold (Penicillium digitatum) and maintaining the quality of Navel oranges during cold storage and subsequent shelf-life. In vitro assays demonstrated concentration-dependent inhibition of P. digitatum mycelial growth, with 16 mM SA and 62 mM CS reducing colony growth by 84.4% and 78.9%, respectively. Scanning electron microscopy confirmed structural damage to fungal hyphae, including deformation, shrinkage, and collapse, particularly following chitosan treatment. On fruit, postharvest dips at the highest concentrations significantly reduced disease incidence and lesion expansion under both natural infection and artificial inoculation conditions. Specifically, 16 mM SA maintained natural disease incidence at 1.67% after 30 days of cold storage plus 5 days of shelf-life, whereas control fruit experienced severe infection approaching 100% under artificial inoculation. Mechanistically, SA and CS treatments induced biochemical host defenses in the fruit flavedo by increasing total phenolic content and elevating the activity of defense-related enzymes, peroxidase (POD) and polyphenol oxidase (PPO). Furthermore, treatment with 16 mM SA and 62 mM CS effectively maintained fruit physical quality by reducing weight loss (3.44–4.23% vs. 9.82% in control after 30 days) and delaying loss of firmness (up to 5.49 kgf vs. 2.79 kgf in control). Physicochemical analysis after 30 days showed higher titratable acidity and improved retention of ascorbic acid (up to 53.90 mg/100 g FW with 16 mM SA), alongside lower TSS/TA ratios compared to untreated controls. Overall, high-concentration postharvest applications of SA (16 mM) and CS (62 mM) represent effective elicitor-based strategies for suppressing green mold, enhancing biochemical defenses, and preserving the physical and nutritional quality of Navel oranges during prolonged storage.