Effect Of Exogenous Myo-inositol On Apple Fruit Quality And Drought Resistance

China is a large apple（Malus×domestica）producing country,with apple planting area and output accounting for about 50%of the world.Many areas regard apple production as an important starting point and measure for local rural economic development and rural revitalization.However,due to the low preferential fruit rate in China,apple is always in a passive position in the market transaction.In addition,because of the low annual precipitation and unbalanced periodic distribution in the Loess Plateau region,the main apple producing area in China,water deficit has also become an important factor that seriously restricts the quality of local apple production.Myo-inositol is a bioactive substance that exists widely in plants.Studies have shown that myo-inositol and its derivatives play an important role in plant signal transduction,stress response,maintenance of cell wall and cell membrane functions,and mediation of auxin transport,and myo-inositol is simple to prepare,inexpensive,so it can be widely used in apple production economically.Therefore,in this study,adult apple trees of Fuji,Honeycrisp and annual seedlings of Malus hupehensis Rehd.were used as experimental materials respectively.Through exogenous myo-inositol treatment,the effects of myo-inositol on improving apple fruit quality,calcium ion absorption and utilization and drought resistance of seedlings were explored,providing theoretical basis for the application of myo-inositol in apple production.Specific research results are as follows:1.Exogenous myo-inositol can improve the fruit quality of Fuji apple.The results showed that 500μM exogenous myo-inositol treatment had the best effect on improving apple fruit quality,and the fresh fruit weight,vertical and horizontal diameter,fruit coloring,fruit hardness,partial soluble solids and ascorbic acid content of apple fruit were improved to a certain extent after treatment.In addition,two myo-inositol treatments were compared:1)once a month treatment from young fruit stage until harvest;2)The fruit was treated three times every 10 days one month before harvest.The latter had more significant effects on ascorbic acid content,while the former had more significant effects on fruit fresh weight,vertical and horizontal diameter,fruit coloring,fruit hardness and partial soluble sugar.2.The combined treatment of myo-inositol and 0.5%Ca（NO₃）₂ at young fruit stage could enhance the absorption and utilization of calcium ions in Honeycrisp apple.It was found that the combination of 500μM myo-inositol and 0.5%Ca（NO₃）₂ had the best promoting effect on calcium ion absorption and utilization.The treatment significantly increased the calcium content of Honeycrisp apple fruit,and increased the single fruit fresh weight,vertical and horizontal diameter,fruit coloring,fruit hardness,total soluble solids,glucose,galactose and sorbitol contents to varying degrees,decreased the titratable acidity content,ultimately enhanced the fruit quality.3.Under short-term drought stress,50μM exogenous myo-inositol pretreatment could enhance the drought resistance of Malus hupehensis Rehd.seedlings.Compared with the apple plants without myo-inositol pretreatment,the plants pretreated with myo-inositol had a lighter degree of wilting,higher relative water content（RWC）,lower relative electrolyte leakage and malondialdehyde（MDA）content.In addition,the exogenous myo-inositol also reduces the chlorophyll content decrease,alleviate the harm of drought stress on photosynthetic ability,and it could enhance the activity of antioxidant enzymes,accumulate more osmotic regulators such as sucrose,glucose,galactose,and proline,thereby alleviating the oxidative stress and osmotic stress suffered by plants under drought stress.