Study On Rapid Formation And Axillary Bud Germination Of Apple Trees Grafted On Dwarfing Rootstock

High density planting of apple trees with dwarfing rootstocks is the developing direction of apple industry in China.Compared with the advanced countries of the cultivation,the production of apple with dwarfing rootstocks in China lacks high-quality grown seedlings with shoots.In addition,the axillary buds currently formed on newly planted young trees are late-mature buds,which are difficult to germinate and form the shoots.Therefore,promoting axillary bud germination of young apple trees with dwarfing rootstocks to accelerate the rapid production of young trees is the key way to achieve early fruiting and high-yield in China.It is of great practical value and theoretical significance to study the effect of applying exogenous chemicals on the rapid formation of young apple trees grafted on dwarfing rootstocks and axillary bud germination.In this study,1～2-year-old Red Fuji young trees with dwarfing rootstocks were used as test materials to study the effect of applying Chouzhibao on the rapid formation of young trees under different central trunk length and lateral branchs length.The differences of endogenous hormone content in the process of promoting the germination of axillary buds between Chouzhibao and the control were analyzed.The transcriptome sequencing and different genes expression were carried out during the germination of axillary buds after applied Chouzhibao.The main results are as follows:1.The 2-year-old Red Fuji seedlings were used as the test material.Chouzhibao was applied after the extended shoots length of the central trunk reached 40～60cm long,the result showed that the ratio of shoots to trunk was the smallest,the total shoots amount was the most,and the main shoots was the medium short shoots.The number of the third shoots was 11.6,which was 2.42 times higher than that of the extended shoots length of the central trunk to 60～80cm,and the difference between the two treatments was significant(p<0.05).When applying after the length of lateral branchs reached 20～30 cm,the number of short shoots in the second and third shoots were significantly more than that of lateral branchs when applying after the length of lateral branchs reached 30～40 cm and 40～50 cm.The ratio of shoots diameter to trunk diameter was smaller than that of the other two treatments,and there was no significant difference in tree height and trunk diameter among the three treatments.2.The 1-year-old Red Fuji seedlings were used as the test material.When applying after the length of the extended shoots of the central trunk reached 70～80cm,the amount of newly formed shoots was the highest with lower ratio of medium to long shoots,and the amount of the secondary shoots was 4.75 times higher than applying when the shoots were 90～100cm.Trees applied with Chouzhibao when lateral branchs reached 40～50cm showed the best growth potential.,with the tree height of 183cm and the trunk diameter of 22.32mm,the ratio of shoots diameter to trunk diameter was 0.61.The length of the secondary shoots and the tertiary shoots and the ratio of middle to long shoots were better than the other two treatments.3.The transcriptome sequencings of apple axillary buds of control and Chouzhibao applied on the 2th and 6th day were carried out Chouzhibao,463165116 pairs of clean reads were obtained.The number of high abundance genes was the most in the axillary buds of 2 days after applying Chouzhibao,Specially expressed genes were the most in the axillary buds 6 days after applying Chouzhibao,at the amount of 656.The results of COG database comparison showed that the differentially expressed genes were partially enriched in signal transduction mechanisms,carbohydrate transportation and metabolism.GO analysis showed that metabolism and cell processes played an important role in response of apple axillary buds to the stimulation of chuchibao.The results of KEGG classification showed that the differential genes involved in plant hormone signal transduction pathway,phenylpropane biosynthesis pathway,starch and sucrose metabolism pathway and carbon metabolism pathway.The results of qRT-PCR verification of 9 randomly selected genes show that the transcriptome sequencing results are reliable.4.The germination of apple axillary buds is related to the variation of endogenous hormones.The content of IAA in axillary buds of apple increased slowly from 3 to 48h after treated with Chouzhibao,which was significantly lower than that of CK(p<0.05).The content of IAA increased to the highest level 96h after treatment,and there was no significant difference with CK.The content of endogenous iP increased from 0 to 12h,and peaked at 12h,which was significantly higher than CK(p<0.05).There was no significant difference in the content of endogenous DHZ between the two treatments in the process of axillary bud germination.The content of ZT in the axillary bud increased significantly from 48 h to 96 h(p<0.05).The IAA/ZT value of Apple axillary buds treated with Chouzhibao decreased significantly during 12～96h,and the IAA/ZT value of apple axillary buds treated with Chouzhibao was constantly lower than that of CK.5.The relative expressions of auxin signal transduction related genes(IAA4、GH3.1-1、GH3.1-2)and cytokinin signal transduction related genes(ARR5、ARR17、ORR9、ORR10)were measured.The results showed that the relative expressions of auxin signal transduction related genes was up-regulated to the highest level 3h after treated with Chouzhibao,and then down regulated.The relative expression of cytokinin signal transduction related genes was up-regulated to the highest level 12h after treatment,then down regulated,and up regulated at 144h after treatment.The results showed that auxin signal transduction related genes played an important role in the activation of apple axillary bud germination.The germination of apple axillary buds is related to the up-regulated expression of the cytokinin signal transduction related gene of A types ARR.