Effects of Preharvest and Postharvest Salicylic Acid and Oxalic Acid Treatment on the Long Cold Storage Quality of ‘Lane Late’ Navel Oranges and ‘Summerina’ Mandarins

Preharvest and postharvest treatments are widely used to maintain citrus fruit quality during extended cold storage. This study evaluated the effects of pre- and postharvest applications of salicylic acid (SA) and oxalic acid (OA), applied separately and in combination, on the quality of ‘Lane Late’ navel oranges and ‘Summerina’ mandarins at harvest and stored at 1 °C for 10 weeks followed by 1 week at 20 °C. Fruit quality attributes, including weight loss, fungal decay, firmness, total soluble solids (TSS), titratable acidity (TA), electrolyte leakage, and biochemical markers, were assessed. Overall, treatments had limited and inconsistent effects on most quality parameters, with no significant differences observed in chilling injury, respiration rate, ethylene production, ethanol content, vitamin C content, malondialdehyde content, or colour. At harvest, oranges subjected to preharvest OA treatments had lower TSS and TA, while peel antioxidant capacity (AOC) was lower for oranges treated with preharvest SA or OA. After storage, postharvest SA reduced calyx stem-end rot by 30% in mandarins. Electrolyte leakage was reduced by preharvest SA in oranges and postharvest OA in mandarins, indicating improved membrane stability. No consistent synergistic effects were observed for combined treatments, and responses varied between cultivars, highlighting the importance of cultivar-specific optimisation. These findings indicate that SA and OA provide limited but targeted benefits under extended cold storage conditions.