Study On Branching Characteristics And 6-BA Regulation Effect Of Different Apple Varieties

Rational and effective branching can promote early fruiting as well as high yield and quality in apple orchards.Branching status is one of the most important criteria for evaluating quality seedlings.Different varieties and stages of development have an vital influence on the branching characteristics of seedlings,but there is still limited research on this.In view of this,this study investigated the branching characteristics of new and superior varieties in their natural state and the effects of 6-BA treatment on the branching characteristics of different varieties,periods and nodes,with a view to providing a theoretical and technical support basis for the establishment and optimization of new techniques for apple branching control in different varieties and growth states.1.The branching characteristics of six new excellent varieties,‘Huashuo’,‘Ruixianghong’,‘Ruixue’,‘Qincui’,‘Venus Golden’and‘Luli’,were investigated in their natural state.The results showed that the effective number of branches（≥15 cm）ranged from 0.8（Luli）to 3.6（Ruixianghong）.The branching angle ranged from 29°（Huashuo）to61.3°（Ruixianghong）,indicating that they differed significantly.In the natural state,the IAA content in the axillary buds of‘Ruixianghong’was dramatically higher than that of‘Huashuo’,at the same time,Me JA and GA₃content were significantly lower than that of‘Huashuo’,while ABA and ZR content were not significantly different.Therefore,it is speculated that the differences in IAA,Me JA and GA₃contents may be related to the branching characteristics of different varieties.2.The treatment of different varieties with different concentrations of 6-BA revealed that the six new superior varieties were unbranched at 1mmol/L,while in the 5mmol/L and2.5 mmol/L treatments,After germination 56 d treatment of’Huashuo’produced branches of1.42 and 0.27,’Qincui’produced 1 branch,’Luli’and’Venus Golden’produced no branches;’Ruixianghong’treated after germination 114 days produced 3.73 and 3.11 branches,and’Ruixue’produced 0.27 and 0.13 branches.Therefore,’Ruixianghong’is a 6-BA sensitive variety,’Huoshuo’and’Qincui’are 6-BA more sensitive varieties,and’Luli’,’Venus Golden’and’Ruixue’are 6-BA insensitive varieties.3.The results of 6-BA treatment on branching at different nodes（with different levels of maturity）suggested that the number of branches at the upper nodes（1～6 nodes）and middle nodes（7～13 nodes）was 5.67 and 2.42,respectively,with their branching rate decreasing from 94.5%to 40.33%,while no effective branches were found at the lower nodes（15～20 nodes）.This indicates that the branching rate,branch length,branch thickness and number of branches all implied a decreasing trend with increasing node position.Compared to the control,in the axillary buds of the upper nodes,IAA and ZR together with ABA contents increased and decreased apparently at 48 h and 96 h,respectively,while Me JA and GA₃contents increased signally at 96 h.In the axillary buds of the middle nodes,the contents of IAA and ZR as well as GA₃decreased at 96 h and 48 h,respectively,meanwhile,the content of ABA decreased observably at both 48 h and 96 h,while the content of Me JA did not differ markedly at 48 h and 96 h.In the axillary buds of the lower nodes,IAA and ABA contents were memorably reduced at 48 h and ZR contents were notably increased at48 h and 96 h,while Me JA and GA₃contents were not prominently different.These results suggest that branch maturity may regulate axillary bud germination by influencing endogenous IAA,ZR and other hormone contents.4.After the treatment of Fuji/M26/Malus×robusta（Carri?re）Rehder,the number of effective branches gradually decreased with increasing treatment time（78 d（B-1）,88 d（B-2）,111 d（B-3）and 129 d（B-4）after sprouting）,in the order of 4,4,3.9 and 0.The results of endogenous hormone measurements in axillary buds reveal no prominent difference in ZR content among the four treatment periods,in addition,IAA and ABA contents were memorably higher in B-2 and B-3 periods than in B-1 and B-4 periods,while IAA,Me JA and ABA contents were higher in B-2 period than in B-3 period with no significant differences.This indicates that the vigorous branch growth period of 78～111 d after budding is an effective period for branch promotion.5.The statistical results of the five different combinations of 6-BA treatments displayed that all combinations promoted branching,while the branching rate was above87%.6-BA（5mmol/L）+GA₄₊₇（3mmol/L）+SL1（0.02mmol/L）treatment showed a difference of only 0.1°in branching angle from 6-BA（5mmol/L）+GA₄₊₇（3mmol/L）+SL2（0.002mmol/L）,even so,seedling height,branch length and branch thickness were superior at 197cm,11.4mm,10.58cm and 3.03mm,respectively,making it the best combination of branching promotion treatment in this study.