EFFECT OF PREHARVEST GIBBERELLIC ACID AND CALCIUM APPLICATIONS ON ON-TREE STORAGE OF SATSUMA MANDARINS

Late harvest of ‘Satsuma’ mandarin fruit may affect the quality and promote fruit drop. This study carried out for two years was aimed at determining the effect of preharvest gibberellic acid (GA₃) and calcium applications on on-tree storage of Satsuma fruit. Gibberellic acid (GA₃, 10 ppm) and Ca (CaCl₂.2H₂O, 2%), their combined application and GA₃ application repeated twice were tested on Satsuma mandarin (Citrus unshiu Mar. ‘Owari’) budded onto trifoliate orange rootstock. GA₃ was applied two weeks before the color break and at color break whereas Ca was applied at color break stage. Control trees were sprayed with surfactant added water. The first harvest was performed at the usual harvest period for the region, and additional two harvests were made at monthly intervals. At each harvest, fruit samples were analyzed for specific gravity, peel color, chemical composition of fruit juice and electrolytic leakage of peel. Starting from the second harvest, fruit number was determined, and fruit drop rate was calculated. Some of the significant quality losses including puffiness were reduced on trees treated with GA₃ twice. Fruit drop could also be prevented with GA₃ treatments. Fruit skin color advanced rather slowly in GA₃ applied trees however this effect became non-significant towards the end of the storage period. Ca applications alone did not exert major effects. On the other hand, all treatments with GA₃ had positive effects in terms of on-tree storage.