Integrated melatonin, calcium, and nitric oxide treatment strengthens mango chilling tolerance through enhanced stress responses and upregulation of key protective genes

• MT+CaCl₂+SNP enhanced chilling tolerance in mango • Treatment reduced chilling injury, respiration, ethylene, and weight loss • Firmness and color retention improved under MT–Ca–NO treatment • ROS accumulation decreased with higher POD and lower MDA levels • Cold-responsive and ethylene-related genes were effectively regulated Chilling injury (CI) severely limits the postharvest quality, storability, and marketability of mango fruit. This study evaluated the combined effects of MT (100 μM), CaCl₂ (0.01 M), and sodium nitroprusside (SNP; 0.01 M) on ‘Langra’ mango stored at 4 ± 1°C for 28 days. The integrated MT + CaCl₂ + SNP treatment substantially mitigated CI, reducing the CI index by 77.62 % relative to control, while improving fruit quality, including 55.24 % lower weight loss, 50.10 % higher firmness, 9.56 % reduced respiration rate, 50.00 % lower ethylene production, and better retention of ascorbic acid. Oxidative stress was effectively controlled, evidenced by a 45.96 % reduction in malondialdehyde (MDA) and increased endogenous MT in both peel and pulp. Biochemical defenses were strengthened, with peel and pulp showing elevated total phenolics, total flavonoids, enhanced H₂O₂ and O₂•⁻ scavenging, and increased activities of phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL), supporting structural and oxidative protection under chilling stress. At the molecular level, MT + CaCl₂ + SNP upregulated cold- and stress-responsive genes ( MiCBF1, MiPOD, MiPAL ) and MT biosynthesis genes ( MiASMT, MiSNAT ), while modulating ethylene signaling genes ( MiETR1, MiERS1 ) consistent with reduced ethylene production. These results demonstrate that the interplay of MT, Ca²⁺, and NO enhances physiological stability, antioxidant capacity, and gene-mediated defense, providing an effective postharvest strategy to mitigate CI in ‘Langra’ mango and offering a foundation for future integrative approaches to improve cold tolerance in tropical fruits.