Effects Of Drought On Apple Quality And Its Relationship With Sugar Metabolism

Northwest Loess Plateau regionis the main apple production areainChina.Water is the key ecological factor in the area.And furthermore,sugar metabolism is the basis of apple yield and quality.Therefore,it is very important to study the effect of drought on the quality of apple and its relationship with sugar metabolism.Seven-year-old‘Gala'appletrees grafted on M.26 self-rooted rootstock which are growing in plastic pot were used in this study.The two drought treatments was settingrelative water content of soil as 50% ~60% and 60%~70% with 70% ~80% as a control.During the treatment period,the chlorophyll,leaf water potential,fruit quality,soluble sugar and related enzyme system were determined with the results as follows:1.Soil water content had a great influence on apple leaf water potential and chlorophyll content.During the treatment period,the water potential and chlorophyll content of apple leaves decreased significantly with the degree of drought deepening.2.Drought treatment affects the growth and development of fruit.The results of fruit shape index showed that there is no significant effects of drought on fruit shape index in young fruit period comparing with contrast.In addition,drought had an increased effect on fruit hardness and soluble solids from young fruit period had been turned out by determination,while the contents of titratable acid in fruit had a decreasing trend.Moreover,the weight of fruit reduced in young fruit period with drought treatment,nevertheless,no significant effect of mild drought stress on it had been found after fruit developing period.3.According to determination ofcontents of Sucrose,Glucose,Fructose and Sorbitol in apple fruit,mild drought significantly increased fructose and sorbitol contents.The drought stress increased the content of sucrose with no effect on the glucosefrom young fruit period.However,the sucrose content decreased and glucose increased due to drought stress after fruit developing period.4.The determination of enzymes related to sugar metabolism in apple fruit showed that mild and moderate droughthad increased the activities of sucrose synthase(SS)and sucrose phosphate synthase(SPS),meanwhile,the activity of acid invertase(AI)had been increased by moderate drought from young fruit period,in addition,increasing enzyme activity of neutral invertase(NI)and steady trend of sorbitol oxidase(SOX)had been found with mild and moderate drought after fruit developing period.Besides,if drought treatment began after fruit developing period,moderate drought would enhance the enzyme activity of AI,moreover,the enzyme activity of SOX would be increased by mild and moderate drought.These results indicate that appropriate drought can improve the hardness and soluble solids content,reduce acid content,but there is a certain influence on fruit size and yield.The drought treatment afterfruit development period had merely significant influence on yield while improving the quality of fruit.In that case,appropriate water control is recommended in laterfruit development period for producing.