Effect Of Different Concentration Of Gibberellin（GA₃） On Fruit Shape Of‘Gala’ Apple

With the increasing demand for high quality and high grade fruits in the market,people pay more and more attention to the appearance quality of fruits.High-quality and high-grade apples are favored by people.Fruit shape,as an important appearance character of apple,largely determines its market economic value and fruit farmers’income.In order to explore the internal mechanism of regulating apple fruit shape index,a large number of long fruit and flat fruit were collected from the offspring populations of’Zihong No.1’and’Gala’apple hybrids,and the contents of the main endogenous hormones CTK,IAA and GA in long and flat fruit were measured during the development period.The results showed that the content of endogenous GA in long and flat fruit was the largest difference,and the main component of gibberellin was GA₃.Therefore,GA₃ with different concentrations of 50 mg·L^-1,250 mg·L^-1 and 500 mg·L^-1was sprayed on’Gala’apple at flowering stage.By measured the changes of fruit shape index at the development stage and fruit hardness,peel flavonoids,anthocyanin,soluble sugar and titratable acid after ripening,the optimal concentration of exogenous gibberellin GA₃ to improve fruit shape index without reducing the comprehensive quality of fruit was investigated,and the gene expression of key enzymes in the endogenous GA synthesis pathway was measured by real-time fluorescence quantitative technology.The internal reasons for the improvement of fruit form index are analyzed.The main analysis results showed that:1.Exogenous GA₃ spraying at different concentrations promoted the elongation of pulp cells and increased the fruit shape index,and T2 treatment had the largest fruit shape index at all stages,that is,250 mg·L^-1 treatment had the best effect.Fruit hardness T1>T2>CK>T3,fruit anthocyanin content T2>T3>T1>CK,fruit flavonol content T2>T3>T1>CK,fruit titratable acid content T1>T3>T2>CK,fruit soluble sugar content T2>CK>T3>T1.In conclusion,spraying 250 mg·L^-1 exogenous GA₃ was beneficial to improve fruit shape index and fruit comprehensive quality.2.The expression levels of CPS,KO,KAO and GA3ox in the endogenous GA synthesis pathway could be increased by spraying exogenous GA₃ at different concentrations.As the key enzyme synthesized by endogenous GA in protoplasts,the expression level of CPS was T2>T3>CK>T1,and the difference between T2 treatment and other treatments was significant.KO and KAO are the key enzymes synthesized by endogenous GA in the endoplasmic reticulum The expression level of KO is T2>T3>CK>T1,and the expression level of KAO is T1>T2>T3>CK.T2 treatment is between other treatments but significantly different from CK.GA3ox is the key enzyme in the last step of endogenous GA synthesis.Its expression level is T2>T3>T1>CK,and the difference between T2 treatment and CK is very significant.In conclusion,T2 treatment could significantly increase the expression of endogenous GA synthetase gene in fruit,and thus improve the fruit shape index of’Gala’apple.