Study On The Graft Compatibility Identification And Early Prediction Indexes Between ’3-45’ Interstock And ’Tianhong 2’ Apple Scion

The survival and growth vigor of apple trees are affected by the graft compatibility between the stock and scion.The consequence induced by incompatible in the later period of apple trees between the stock and scion is very serious,which greatly restricts the application of grafting in actual production and can cause huge economic losses.At present,there are few researches on incompatibility in the later stage of grafting combination and a complete set of measurement standards for grafting incompatibility in later stage has not been formed.Therefore,it is significant to further explore and discuss the early predictive indicators of incompatibility in later stage of grafting.In this experiment,we took two grafting combination(the rootstock was Baleng Crabapple as,the interstocks were ’3-45’and ’Jizhen 2’,respectively,and the scion was Tianhong 2’apple variety)as test materials.Physiological and biochemical indicators related to grafting compatibility were measured in the graft interface and leaves were measured,and the transcriptome of sampled leaves was detected to discover the differentially expressed genes related to grafting compatibility.The main results are as follows:1.The survey results of four rootstock combinations of Tianhong 1’ and Tianhong 2’were grafted on ’Jizhen 2’ and ’3-45’ as intermediate stocks showed as follows:In the second year after grafting,the growth vigor of ’Tianhong 2’/’Jizhen 2’ Baleng Crabapple was significantly better than that of Tianhong 2’/’3-45’/Baleng Crabapple,which died in later period.At the experiment site in Yixian County,the mortality rate of this grafting combination apple trees was 22.22%,55.56%and 100%,respectively,in the second,fourth and fifth year after grafting.However,there is no significant difference in the growth vigor of the two combinations of ’Tianhong 1’/’Jizhen 2/’ Baleng Crabapple and Tianhong 1’/’3-45’/Baleng Crabapple,and neither combinations showed dead in later period.We speculate that the incompatibility of the grafting combination that Tianhong 2’/’3-45’/Baleng Crabapple is caused by the grafting of Tianhong 2’ on the interstock ’3-45’.2.The activities of SOD,POD,CAT,PPO,PAL and related enzymes of the grafting interface and leaves of different grafting combinations were analyzed,and the results showed that,the higher the compatibility in later stage of grafting,the higher the enzyme activities of SOD,POD,CAT and PAL in the graft interface and leaves,while the PPO enzyme activity is opposite.According to principal component analysis,SOD,POD and PAL can be used as early predictors of incompatibility in later stage of grafting3.The auxin,cytokinin,gibberellin and other hormones on the grafting interface and leaves of different grafting combinations were analyzed,and the results showed that,the content of auxin and cytokinin of the grafting interface and leaves of compatible stock-scion combination is higher than that of the incompatible stock-scion combination,while gibberellin is the opposite.According to principal component analysis,auxin and cytokinin have the greatest influence on grafting compatibility and can be used as early predictors of incompatibility in later stage of grafting.4.The analysis of catechins,epicatechins,cinnamic acid,chlorogenic acid,caffeic acid and coumaric acid on the grafting interface and leaves of different grafting combinations showed that:the higher the grafting compatibility,the higher the catechins content in the grafting interface,while the lower the content of other phenolic substances.In the leaves,the higher the compatibility at later stage of grafting,the lower the content of various phenolic substances.According to principal component analysis,caffeic acid and catechins can be used as early predictors of grafting compatibility in later stage.5.The transcriptome analysis identified 450 DEGs(321 up,129 down)between the compatible and incompatible stock-scion combinations.According to GO and KEGG analysis,the main enrichment pathways were flavonoid biosynthesis pathway,phenylalanine metabolism pathway,phenylpropane biosynthesis pathway,plant hormone signal transduction pathway,phenylalanine,tyrosine and tryptophan biosynthesis.According to comprehensive analysis,the pathways related to the grafting compatible a later stage included that,flavonoid biosynthesis pathway,phenylalanine metabolism pathway,phenylpropane biosynthesis pathway and plant hormone signal transduction pathway.Among them,MD15G1288600(MdMYB44)、MD01G1236300(Md4CL4)、MD04G1096200(MdPAL1)、MD11G1241100(MdPOD47)and MD17G1081000(MdGH3.10)may participate in the apple grafting compatibility reaction.