Effects of pre-harvest GA3 spraying on yield, quality and storability of mango fruit

【Objective】To test the suitable concentration and timing of gibberellin (GA₃) application on mango trees (Mangifera indica L.‘Guifei', an early-maturing cultivar) at fruit growth and development period, we compared the effects of GA₃ spraying at different concentrations on yield, quality and postharvest storage characteristics of the mango fruits. GA₃ is used by fruit growers to increase production due to its effects on promoting fruit enlargement and enhancing coloration. However, with abuse usage of GA₃, many farms produced quite a lot of stay-green fruits at ripening in 2011. Our previous studies on the effects of multiple plant growth regulators using in fruits production by farmers on postharvest ripening of mangofruits indicated that high concentration of GA₃ spraying could induce stay-green at ripening and reduction of fruit quality in‘Guifei'mango.【Methods】Health‘Guifei'mango trees with consistent size and vigor were selected from a commercial orchard located in Dongfang city, Hainan province of China. The age of the trees was about 12 years old. GA₃ at concentrations of 50 mg·L^-1, 100 mg·L^-1and 250 mg·L^-1were sprayed each one time at 15 d, 25 d and 35 d after flowering with clean water serve as the control. Three trees were selected for one treatment (3 repetitions) . Random group was arranged. The fruits were harvested at 113 d after anthesis when reached commercial value (physiological maturity) , then loaded in corrugated carton box, each layer of fruits were placed soft paper to avoid damage. After that the fruits were taken back to laboratory immediately, storaged in a room under 25±1 ℃ and 85%±5% relative humidity (RH) . Fruit color parameters of fruit peel such as L value, a value and b value, the contents of total chlorophylls, anthocyanins, and carotenoids were measured at harvest and during storage to estimate the effect of GA₃ on mango postharvest color changing. Fruit firmness, soluble solid content (TSS) content, titration acid (TA) content, and vitamin C content were measured to estimate the effect of GA₃ on inner quality of mango. The yield, fruit weight (fruit with seed and fruit without seed) , fruit shape index, the fruit number per tree and the disease incidence induced by fungi were tested.【Results】The yield, the number of fruits every tree, fruit enlargement and fruit shape index were increased by GA₃spraying. The yield per tree increased by 23.48%, 19.85% and 11.42%, respectively by using 50 mg·L^-1, 100 mg·L^-1and 250 mg·L^-1GA₃. The number of fruits every tree improved by 9.24% and 20.13%, respectively by 50 mg·L^-1and 100mg·L^-1GA₃ treatment. Reverse effect was induced by 250 mg·L^-1GA₃ which was decrease the number of fruit by 4.62%. The weight of fruit increased effect was obviously higher on the fruit without seed than on the fruit with seed. The weight of seedless fruit were increased by 23.48%, 19.85% and 11.42%, respectively after spraying 50 mg·L^-1, 100 mg·L^-1and 250 mg·L^-1GA₃ compared with the control, and the weight of seed fruit were increased by 2.35%, 5.26% and 6.20%, respectively. The effect on fruit shape index by GA₃ was noticeable on the fruit without seed compared with the fruit with seed. GA₃250 mg·L^-1spraying induced the shape index of fruit with seed increased by 3.15% and fruit without seed increased by 6.20%. GA₃ spraying during fruit growth affected the content of pigments on mango peel and the fruit color development during maturation and ripening. At harvest, the L value, a value and b value were no obvious difference between the treatments (GA₃: 50 mg·L^-1, 100 mg·L^-1and 250 mg·L^-1) and the control, but at ripening their values of the treatments were all lower than the control. At harvest (physiological maturity) , the content of chlorophylls and carotenoids on peel were reduced by GA₃, and the content of anthocyanins was increased. The effect on fruits treated by GA₃250 mg·L^-1was more obvious and the content of chlorophylls and carotenoids were decreased by 4.87% and 5.46 %, respectively. The content of anthocyanins treated by GA₃250 mg·L^-1was improved by 19.24% and the fruit color was more bright red. At ripening, the contents of chlorophylls and carotenoids on peel were improved by GA₃, and the increase of treatment GA₃250 mg·L^-1were by 136.37% and 9.88% respectively. The content of carotenoids by GA₃250mg·L^-1was decreased by 3.78%. The color changing from green to yellow was inhibited by GA₃ during storage. The effect on fruit quality was not evident by GA₃50 mg·L^-1, while the fruit quality treated by GA₃250 mg·L^-1was reduced. The fruit firmness and TSS content of treatment 250 mg·L^-1GA₃ decreased by11.76% and 5.07% respectively compared with the control, and the acid content increased by 18.85%.The postharvest disease incidence rate was enhanced by GA₃, and the incidence of anthrax and stalk rot of fruits treated by GA₃250 mg·L^-1were increased by 327.55% and 95.45%, respectively.【Conclusion】GA₃ (50 mg·L^-1and 100 mg·L^-1) spraying during fruit development increased the yield of‘Guifei'mango, pro- moted fruit enlargement, improved fruit shape index, but declined fruit quality reflecting by decreasing TSS content and fruit firmness while increasing TA content and disease incidence.High concentration of GA₃ (250 mg·L^-1) induced stay-green fruit with no obvious effect on yield.These results suggest that the suitable concentration of GA₃ spraying at fruit growth and development time is 50mg·L^-1, which could increase the fruit weight and yield without decrease fruit quality.