The Physiological Mechanism Of PBO On Promoting Flower Bud Differentiation Of ’Fuji’ Apple Tree

The The apple（Malus domestica Borth.）cultivar‘Fuji Nagafu No.2’and‘GalaFuhongzaoga’were used to spraying PBO（2857mg/L、4000mg/L、6667mg/L）in10thApril,10th May,10th June（CK: Spraying water）, in order to compare the effects offlowering rate and branch of class in different treatments. Measuring the growth ofmorphological indicators of young apple tree; Weighing or calculating related leaf qualityindicators of young apple tree; counting bud broken of different parts of the branches andflower formation situation. The results showed that（1）when spraying PBO at4000mg/L twoto three times, the flowering rate of‘Fuji’and‘Gala’will increase Significantly and thenumber of short shoots will increase and ratio short shoots to long shoots will increasecompared to spraying water（.2）when spraying PBO at6667mg/L, the growth of plant heightand crownshaft per year in‘Fuji’and‘Gala’young apple tree was significantly inhibited,while the two varieties of diameter of cultivar trunk growth per year was a significant increase;Spraying PBO significantly inhibited the growth of the length of main branch in‘Fuji’and‘Gala’, significantly inhibited the growth of diameter of main branch in‘Fuji’, but thegrowth of diameter of main branch in‘Gala’was not inhibited significantly; PBO sprayingtreatment inhibited the growth of shoots of upper, middle and basal tiers in Fuji treesthroughout the growing season while its inhibitive influence on ‘Gala’was not significantbecause shoots growth of Gala trees stoped earlier by nature.（3）Compared to controltreatment, PBO spraying treatment at6667mg/L can significantly increase leaf fresh weightper100from July to October and leaf dry weight per100from J July to August in ‘Fuji’,For Gala varieties having the same result from June to September for both leaf fresh weightper100and leaf dry weight per100; Whether Fuji or Gala, leaf area per100that sprayingPBO treatment were significantly lower than the control from May to October; In contrast,specific leaf weight that PBO spraying treatment was significantly greater than the controlduring this period except June in Fuji varieties.（4）PBO spraying treatment significantlyimproved the flowering rates and bud broken rates of upper, middle and basal tiers in Fujitrees and in gala trees.The objective of this experiment is to study the effects of spraying PBO at6667mg/Lconcentration on flower formation and N, P and K element content, total sugar content, C/Nratio in leaf and bud of young apple tree, to explore the relationship between young apple tree flower formation and several element content, total sugarcontent, C/N ratio of leaves and buds.And study the effects of spraying PBO with different concentrations on carbohydrate contentchanges of leaf and bud in apple tree. The results showed that（1）The content of N, P and Kand content of total sugar and ratio of C/N of leaf and bud in ‘Fuji’ and ‘Gala’ are closelyrelated with flowering of apple tree. when spraying PBO at6667mg/L three times, thecontent of N, P and K and content of total sugar and ratio of C/N of leaf and bud in ‘Fuji’ and‘Gala’will increase Significantly compared to control during the key date of flower-buddifferentiation（May to mid-june）（.2）Compared with control, PBO spraying treatments withhigher concentrations (4000mg/L and6667mg/L) could increase the content of the sucrose,glucose, sorbitol, total soluble sugar in leaf in upper, middle and basal part of ‘Fuji’youngapple tree in the early growth stage (from May to July), but significantly reduced the starchcontent in leaf during this period. Similarly, given PBO spraying treatment with higherconcentration, the content of sorbitol and total soluble sugar in bud increased significantly inJune and Starch content in bud was significantly reduced in July.（3）Flower bud formation isclosely correlated to the translocation or conversion of carbohydrate between leaf and bud.PBO spraying treatment with highest concentration（6667mg/L）, lead to the significantpositive correlation of sorbitol and total soluble sugar content between leaf and bud; However,the corresponding correlation of starch content between leaf and bud was not significant.According to experiment results and taking production investment into consideration, wepropose that the PBO spraying treatment with4000mg/L is effective in promoting flower budformation of‘Fuji’apple tree in the period from May to July（the critical period forphysiological differentiation of apple flower buds）.