Synergistic Postharvest Efficacy of Methyl Salicylate, Methyl Jasmonate, and Sodium Nitroprusside in Enhancing Chilling Tolerance of Tomato Fruit

Chilling injury (CI) is a major constraint to the postharvest shelf-life of tomato fruit (Solanum lycopersicum L.), leading to severe quality deterioration, which is closely linked to cell membrane damage. While individual postharvest treatments with the elicitors, such as methyl salicylate (MeSA), methyl jasmonate (MeJA), and the nitric oxide donor sodium nitroprusside (SNP), alleviate cold stress, their synergistic potential in combination has not been systematically explored. The present study evaluated the postharvest efficacy of 1 mM MeSA, MeJA, SNP, and their combinations (MeSA + MeJA, MeSA + SNP, MeJA + SNP) on ‘Vivalto RZ’ tomato fruits stored for 20 days at 2 °C, followed by a 2-day shelf-life period at 20 °C. All treatments effectively mitigated quality loss and CI incidence compared to the control. Notably, the MeSA + SNP and MeJA + SNP combinations demonstrated the highest efficacy, resulting in the lowest CI indices (1.2–1.4 vs. 3.4 in control) and the best preservation of firmness and titratable acidity. This enhanced tolerance was correlated with improved membrane integrity (lower malondialdehyde content and ion leakage) and the strongest upregulation of the antioxidant system, specifically achieving the highest ascorbate peroxidase (APX) activity. The combined application of MeSA or MeJA with SNP exerts a synergistic effect that provides superior chilling tolerance, representing a highly effective and commercially viable strategy to extend the postharvest shelf-life of tomato fruit.