Effects of Storage and Preservation of Postharvest Gonggan Mandarin (Citrus reticulata) Fruit Immersion in Salicylic Acid Combined with Calcium Chloride

[Objectives]To investigate the effects and mechanism of fruit immersion treatment with salicylic acid (SA), calcium chloride (CaCl2) solutions at different concentrations or their combinations on post-harvest preservation of Gonggan fruit.[Methods]13 experiments (2 storage temperatures, 3 control treatments, 3 concentrations of SA solution, 4 concentrations of CaCl2 solution and 3 combinations of SA + CaCl2 solution for fruit immersion treatment) were conducted for 90 d. Gonggan fruit weight loss rate, rotting rate, disease index, disease type, soluble solids and organic acids content, and the differences in the activity of six enzymes (APX, PPO, CHI, CAT, SOD, PAL) related to fruit disease resistance were detected regularly. [Results] With the increase of storage days, the weight loss rate, rotting rate and disease index increased, the content of soluble solids and organic acids decreased, the activity of APX, PPO, CHI and SOD increased, and the activity of CAT and PAL decreased. However, the increase or decrease of fruit loss at low temperature was the smallest, and the increase or decrease of fruit at natural room temperature was the largest. Gonggan fruit cleaning before storage is an effective preservation and fresh-keeping technology, but its preservation and fresh-keeping effect is far less than that of fruit immersion by SA, CaCl2 and SA + CaCl2 compound solution. The effect of fruit immersion by SA solution was greater than that of fruit immersion by CaCl2 solution; the best concentration of SA alone was 6.0 mmol/L, which was not significantly different from 3.0 mmol/L, but the effect of 9.0 mmol/L decreased; the best concentration of CaCl2 alone was 6.0 mmol/L, which was significantly better than 3.0 and 9.0 mmol/L; the optimal concentration combination of SA+CaCl2 compound solution for fruit immersion treatment was 6.0 mmol/L SA + 3.0 mmol/L CaCl2. [Conclusions]The fruit immersion by SA, CaCl2 and their compound solutions induced the increase of activity of six enzymes related to disease resistance in Gonggan fruit, and PPO and CHI were judged to be two key enzymes based on response intensity.