Effect Of Different Fruit Thinning Agents On The Thinning Of Young Fruits Of ’Changfu 2’

’Changfu 2’is a high-quality,storable and late-maturing variety of Fuji apples,which is prone to small and large years,and good flower and fruit thinning can slow down the occurrence of small and large years.In recent years,the occurrence of spring chill in apple producing areas in China has become more and more frequent,which has an important negative impact on the chemical thinning of apples.In order to clarify the thinning effect of different thinning agents on’Changfu 2’apples,we investigated the thinning effect of several thinning agents and their physiological and biochemical effects on the tree,with the aim of screening out the thinning agents with good thinning effect on’Changfu 2’and no negative effects on the tree and fruit quality.In this study,the 8-year-old’Changfu 2’with Xinjiang wild apple as the base anvil and M₂₆ as the intermediate anvil was used as the test material.In 2021,naphthalene acetic acid（NAA）,ethephon（ETH）and trichlorfon were used respectively.Three concentration layers were set up in a single spray and superimposed spray when the diameter of the central fruit was about 5 mm and 10 mm.Water and artificial fruit thinning were used as controls.Through the statistics of the fruit thinning rate,it is concluded that the thinning effect of superimposed spraying is significantly higher than that of single spraying,and the fruit thinning rate of spraying with a center fruit diameter of 5mm is generally higher than that of spraying with a center fruit diameter of 10mm.The antioxidant enzymes,sorbitol metabolizing enzymes,soluble sugars and fruit quality of the stacked spray treatments were determined,and NAA（10 mg/L）,ETH（500 mg/L）and trichlorfon（1400 mg/L）were screened for better thinning effect.In 2022,these three concentrations of fruit thinning agents were sprayed superimposed when the center fruit reached 5mm and 10mm,respectively,with water as the control.The fruit thinning rate was counted after physiological fruit drop,and the basal leaves of fruit moss parapodia were collected at 7,17,27,37 and 47 d after spraying to determine the soluble sugar content in leaves,fruit quality of mature fruits,sugar metabolizing enzymes,hormone content and related coding genes Md SPS5、Md S6PDH、Md SDH1、Md SOT1、Md FK1、Md HXK1、Md ARF5、Md GA20ox1 and Md ABF3 in terms of their relative expression.The results of the study showed that:1.1.The 2021 fruit thinning agent screening trial showed that the rate of fruit thinning by superimposed spraying of fruit thinning agent was better than that by single spraying;the fruit thinning effect of fruit thinning agent spraying when the fruit diameter reached 5 mm was better than that of spraying when the fruit diameter reached 10 mm.2.The results of the 2022 trial showed that the fruit thinning rate of 1400 mg/L trichlorfon reached 69%,which was better and could increase the orchard management efficiency.3.Different fruit thinning agent treatments all increased the accumulation of soluble sugars in the basal leaves of the fruit moss parapodia,with NAA treatment being the most significant in accumulating soluble sugars.The sugar-related genes Md SPS5,Md S6PDH,Md SDH1,Md SOT1,Md FK1 were more consistent with the changes of each soluble sugar content.4.After different fruit thinning agent treatments,all of them could up-regulate the contents of IAA,GA₃ and ZR in the basal leaves of fruit moss parapetals in the early stage of treatment,and the changes of ZR were the most obvious,and the contents of ABA increased significantly after 27 d of treatment,and the changes of trichlorfon treatment were the most significant,and the expression of related genes Md ARF5,Md GA20ox1 and Md ABF3 changed with endogenous hormones,which indicated that fruit thinning agents could accelerate fruit abscission from the perspective of hormone The experiment indicated that fruit thinning agents could accelerate fruit abscission from the perspective of hormone regulation.5.Trichlorfon treatment significantly reduced titratable acid and increased single fruit weight and soluble solids compared with the control,and the solid to acid ratio was significantly higher than the other treatments and the control,NAA treatment significantly increased fruit hardness and soluble solids and reduced titratable acid,and ETH treatment significantly increased fruit hardness and reduced titratable acid.To sum up,1400mg/L trichlorfon has the best thinning effect.The thinning rate of two consecutive years of trials exceeds 60%,and it has no negative effect on the tree itself,increases the accumulation of soluble sugar content in the leaves,and affects the leaves compared with the control.Hormone content,reducing GA₃ content and increasing ABA content,synergistically with various hormones,promotes young fruit shedding,and has a more positive impact on the quality of mature fruit.It not only upregulates soluble solids and reduces titratable acids,but also makes the solid acid ratio larger.It can also significantly increase the weight of single fruit and increase the commercial value of fruit.