| In recent years,the dwarfing rootstock and high density orchard systems have been used and developed in the new established apple orchards in China.Xinjiang is one of the most famous apple productions areas in China and now there are more new orchards are planting with dwarfing rootstock rather than vigorous rootstock.However,the performance of apple trees grafted on dwarfing rootstock highly depends on geographical conditions,and related cultivation technologies are rare in Xinjiang.Fruit load control is one of the key technologies for efficient apple tree cultivation.Clarifying the impacts of fruit load on apple canopy morphogenesis,leaf photosynthesis and soluble sugar metabolism is of great significance for the development of efficient dwarfing cultivation technology in southern Xinjiang.Therefore,the’Royal Gala’/M9-T337 apple trees with various fruit load were choose as materials in southern Xinjiang.Then,impacts of various fruit load on apple canopy morphogenesis,leaf photosynthetic capacity and soluble sugar were studied.The result of this study will be helpful for fruit load control and development of dwarfing rootstock in southern Xinjiang.The main results are as follows:1.The range of fruit load in current study is between 0.3 and 8.2 fruits per trunk cross-sectional area(cm~2).The increase of fruit load significantly reduced the cross-sectional areas of trunk and branches and crown width,reducing the numbers and proportions of medium and long shoots and increasing the proportion and number of short shoots.Consequently,increased fruit load significantly increased the total number of shoots and reduced the leaf area index.Except the growth of long shoots was not inhibited when fruit load at extremely low level(0.3 in current study).the length and diameter of leafy shoots under other fruit loads stopped increase after a certain time.The long,medium and short shoots stopped growth at 60,45 and 30 days after full flowering respectively,and the smaller the load,the greater the length and diameter of medium and long shoots.For the annual changes of leaf photosynthesis,the fruit loads at 2.3,4.4,6.1 and 8.2 PCS/cm~2maintained photosynthetic capacity throughout the year,and reached the maximum 90 days after flowering.For the leaf diurnal dynamics of leaf photosynthesis,the leaf photosynthesis peaked at 11:30,and rested at 13:30,irrespectively.The increased fruit load significantly improved the photosynthetic capacity and water use efficiency of leaves.Higher fruit load significantly reduced single fruit fresh weight,fruit shape index,coloring index and soluble solids.the tree with fruit load at 4.4 PCS/cm~2had the best fruit quality,yield(44.38 t/hm~2)and economic income(201900 yuan/hm~2)2.By comparing the three load treatments of 0.3,4.4 and 8.2(fruit/trunk cross-sectional area(cm~2)),the load directly affected the distribution of soluble sugar in new shoots and annual branches.15 days after flowering,the contents of sucrose,glucose and fructose in shoots and leaves loaded with 8.2 PCS/cm~2were significantly higher than those loaded with 0.3 and 4.4 PCS/cm~2.Reducing the load can increase the soluble sugar content of branches and leaves with small leaf fruit distance(fruit platform,fruit platform leaves,fruit platform auxiliary shoots,fruit platform auxiliary shoots and annual vegetative branches)at 15 and120 days after full flowering.In addition,compared with 15 days after flowering,reducing the load at 120days after flowering can effectively accumulate the soluble sugar content of all kinds of branches and leaves(except the sucrose and glucose content of the secondary shoots of the fruit platform and the sucrose content of the secondary shoots and leaves of the fruit platform).3.After comparing the two fruit load treatments of 4.4 and 8.2(fruit/trunk cross-sectional area(cm~2)),the contents of soluble sugar(except raffinose),citric acid,maltitol and L-aspartic acid in fruit increased gradually with the development of fruit and increased with the decrease of fruit load.The contents of organic acids,such as quinic acid and shikimic acid,amino acids such as L-phenylalanine,D-tryptophan,L-proline and L-threonine,decreased gradually with the development of fruit,and decreased with the decrease of fruit load.In addition,the content of malic acid increased first and then decreased with the development of fruit,and reduced the fruit load accelerated the accumulation of malic acid.4.In conclusion,under extremely high source/sink ratio condition,the shoot growth was not affected by temperature-regulated growth rhythm,and the shoot growth dynamics was not affected by source/sink ratios when the fruit load was larger than 2.3 PCS/cm~2in current study.In southern Xinjiang.the optimum fruit load for’Royal Gala’/M9-T337 apple tree is 4.4 fruits per trunk cross-sectional area.This fruit load benefits the formation of canopy morphology,fruit yield and quality,and the accumulation of soluble sugar. |
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