Pre and Postharvest Management to Improve Yield and Quality of "Kinnow" Mandarin

Abstract

Citrus is one of the most important fruit crops in Pakistan. Kinnow mandarin is the leading citrus cultivar of Pakistan. The yield is lower as compared to other advanced citrus producing countries. Poor tree health and nutritional deficiencies are the major causes of lower yield. Poor management practices before and after harvesting can cause serious problems regarding the yield and quality of Kinnow. To overcome these problems, different experiments were planned and executed. The study was divided into three subcategories such as study 1, study 2 (pre-harvest) and study 3 (postharvest). In 1st two studies foliar sprays of calcium chloride, zinc sulphate, gibberellic acid and salicylic acid were applied on the Kinnow trees, four months before fruit harvesting to check their effects on preharvest fruit drop and other fruit quality related parameters. In third study two experiments were conducted to optimize the doses of salicylic acid (2, 3 and 4 mM) and calcium chloride (2, 3 and 4%) as pre-storage treatments to increase the storage period and to minimize the quality deterioration when stored at 5ºC for long term storage. The results showed that 0.5% calcium chloride was found best to minimize the preharvest fruit drop (16.48%) as compared to control where preharvest fruit drop was 49.70%. Maximum yield of 110.03 kg per tree, fruit weight (264.29 g), juice weight (51.53%), TSS (13.13 ºbrix), ascorbic acid contents (43.84 mg100 g-1)), total sugars (16.98%), reducing sugars (6.23%), phenolic contents (341.82 mg GAE100g-1), total antioxidants (91.14% inhibition) were also noted from the fruit of same treatment. Among the zinc sulphate doses 0.6% zinc sulphate exhibited the lowest preharvest fruit drop (10.08%) and maximum yield (120.89 kg) with maximum juice weight (42.23%) and higher TSS (9.50 ºbrix), total sugars (17.37%), reducing sugars (5.99%), ascorbic acid contents (35.46 mg 100g-1), total antioxidants (53.25 %inhibition) and total phenolics (205.33 mg GAE100g-1). Gibberellic acid (30 mgL1) performed best to minimize the preharvest fruit drop (11.82%) and improve the yield up to 1015.77 kg with good eating quality parameters. Salicylic acid (4mM) dose exhibited best results to reduce the preharvest fruit drop (26.16%) and maximize the yield (195.26 kg), fruit weight (232.55 g) and juice weight (50.94%), TSS (13.47 ºbrix), total sugars (14.96%), reducing sugars (5.84%), ascorbic acid contents (47.66 mg 100g-1). The results of postharvest treatments (study 3) indicated that 3mM salicylic acid was performed best to minimize the weight loss from 15.46 to 8.52% and to reduce the fruit rot from 16.12 to 1.40% with higher values of juice weight (48.16%), ascorbic acid contents (42.19 mg 100/g), TPC (207.10 mg GAE 100/g), total antioxidants (64.95 % inhibition) after storage. The antioxidative enzyme such as Catalase (22.76 per mg), Peroxidase (0.63 per mg) and Superoxide dismutase (124.54 per mg) activity were greater at higher dose treatment (4mM SA) after 90 days storage. Moreover, 4% calcium chloride played a important role in reducing the weight loss from 14.59 to 7.39% and reducing the decay percentage from 11.68 to 1.33%. The maximum TSS (9.41 ºbrix), TA (1.66%), ascorbic acid contents (50.95 mg 100g-1), sugars [total sugars (14.90%) and reducing sugars (8.32%)] were also more at same treatment. However, 3% calcium chloride treatment showed best results in juice weight (53.24%), total phenolic (63.17 mg GAE 100/g), TAC (218.44 % inhibition), and fruit quality enzymes [(CAT (25.66 U/mg protein), POD (0.55 U/ mg protein) and SOD (128.26 U/ mg protein). It was concluded that preharvest fruit drop can be minimized with maximum quality related attributes by the foliar spray of 0.5% calcium chloride, 0.6% zinc sulphate, 30 mgL-1 gibberellic acid and 4 mM salicylic acid when applied on Kinnow trees four month before fruit harvest. Moreover, treatments of 3, 4 % calcium chloride and 3 mM salicylic acid before storage is best to retain the quality related parameters of Kinnow fruit during 90 days storage at 5ºC.