EFFECT OF GIBBERELLIN AND SOME ANTIOXIDANTS PRE-HARVEST FOLIAR APPLICATION ON YIELD, FRUIT QUALITY AND SHELF LIFE OF WASHINGTON NAVEL ORANGE

The present study was conducted during 2015and 2016 seasons on ten years old Washington navel orange trees grown in clay soil. Trees were sprayed three times in July, September and November with gibberellic  acid  at 30 ppm as well as  ascorbic acid, citric acid  and salicylic acid each at 400ppm (for the three doses) in order to investigate their effect on tree yield and fruit quality characteristics at harvest and during shelf life (7-14 days). Trees were harvested on the end of February (late season). All sprayed substances delayed fruit peel ageing, fruit color break and decreased pre-harvest fruit drop. Also, results indicated that gibberellic acid treatment increased canopy volume index, shoot length, fruit peel thickness, leaf calcium and fruit peel resistance. Moreover ascorbic acid sprays led to an access in fruit length, fruit diameter, leaf nitrogen, potassium and calcium, Vitam. C, TSS, TSS/acid ratio, leaf area and chlorophyll a and b contents. Ascorbic and citric acid treatments gave higher trunk across, total and reducing sugars. Salicylic acid application enhanced, yield, fruit peel thickness, acidity and fruit peel resistance. Applying previous antioxidants then storaging at room temperature for a week and two weeks revealed that ascorbic acid application increased, Vitam. C, TSS, TSS/acid ratio and total sugars of fruits during shelf life after 1-2 weeks. Also, ascorbic and citric acid treatments increased reduced and unreduced sugars. Citric acid spraying led to an increase of weight loss than all other treatments. Gibberellic and salicylic acid application enhanced fruit peel resistance.  All antioxidants treatments reduced decay during shelf life as compared with control. The TSS, TSS/acid ratio, total and non reducing sugars, fruit weight loss percentage and decay of citrus fruits were increased, whereas acidity, reduced sugar and fruit peel resistance were gradually and significantly decreased by increasing storage periods.