Exogenous salicylic acid induces endogenous SA biosynthesis, enhances osmolyte accumulation, antioxidant defense, and free radical scavenging to alleviate chilling injury in red bell pepper fruit

Chilling injury (CI) is a major postharvest limitation for tropical and subtropical crops such as bell pepper (Capsicum annuum L.), reducing marketability and shelf life under low-temperature storage. This study assessed the effects of preharvest foliar application of salicylic acid (SA) at concentrations of 0, 1, 5, 10, and 15 mM on reducing CI and maintaining the postharvest quality of red bell pepper fruit (cv. ‘Westland, 2090’) stored at 4 °C. Results showed that CI symptoms progressively worsened during storage in untreated fruit, whereas SA treatments, at 5 mM, reduced CI index incidence and preserved superior visual and physicochemical quality. The 5 mM SA treatment lowered the CI index by 76 % (The CI index decreased from 4.60 to 3.06) after 24 d and extended shelf life by 9 d compared to controls. This concentration also reduced weight loss, electrolyte leakage, and the accumulation of reactive oxygen species (hydrogen peroxide and superoxide radicals) and malondialdehyde, indicating improved membrane integrity and reduced oxidative damage. Additionally, 5 mM SA-treated fruit maintained higher firmness, titratable acidity, total soluble solids, vitamin C, antioxidant capacity, and total phenolic content. These benefits correlated with enhanced activities of key antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase, and suppression of lipid-degrading enzymes such as lipoxygenase, phospholipase D, and polyphenol oxidase. Notably, SA treatment stimulated an increase in phenylalanine ammonia-lyase activity and endogenous SA levels, amplifying defense signaling pathways. Increased accumulation of osmoprotectants γ-aminobutyric acid and proline further supported improved cold stress tolerance. Together, these findings demonstrate that preharvest application of 5 mM SA is a practical and effective strategy to mitigate CI and preserve postharvest quality in red bell pepper during cold storage.