Physiological And Molecular Mechanisms Of Graft Union Formation In Blueberry

As a time-honored technology,grafting has formed a mature industrial structure in horticulture and agricultural production.Blueberry is very demanding on the soil environment where it is planted,and it is vulnerable to water stress such as drought and flood.Blueberry seedling cultivation is carried out by establishing clones through tissue culture.The tissue culture seedlings of blueberry are thin,the culture cycle is long,the process of seedling refining and rooting outside the bottle is tedious,and the resistance of the generated advanceless roots is poor.The above factors restrict the planting range of blueberry and seriously affect the further development of the blueberry industry.Therefore,grafting cultivation of rootstocks with developed roots and a wider range of soil pH adaptability is an effective means to broaden the planting area and make blueberry plants more resistant.In this study,by means of field grafting experiment and in vitro grafting experiment,a number of physiological indicators were determined for each experimental group,and the relative expression of key genes of graft formation was analyzed,so as to explore the physiological and molecular mechanism of graft formation of blueberry scion.Specific research results are as follows:(1)The results showed that the survival rate and scion growth of ‘Star' and‘O'Neal'grafted with 'Premier' and ‘Climax'as rootstocks were significantly higher than those of other combinations,and Premier and Climax were excellent rootstocks for blueberry grafting.The activities of PAL,PPO,POD and SOD in the leaves of scions at different stages after grafting were determined,At 540 DAG,the enzyme activity of PPO and PAL was positively correlated with that of ‘Star/Premier',and the correlation coefficient was 0.677,the correlation coefficient between the survival rateand the grafting combination with‘O'Neal' as scion was 0.738;The correlation coefficient between PAL enzyme activity and grafting survival rate of ‘Star' was0.680,and that of ‘O'Neal' was 0.584;the correlation between survival rate and POD,SOD enzyme activity was small.(2)The observation results of paraffin sections of in vitro grafting showed that autografting had better compatibility than allograft,and the compatibility of the grafting combination of ‘O'Neal/Sharpblue'was better than that of‘O'Neal/Premier'.Callus began to appear at the grafting surface of self-grafting combination at 21 days after grafting,callus increased significantly at the grafting surface of self-grafting at28 days after grafting,and there was a small amount of callus at the grafting surface of autograft.The graft union is connected without vascular bundles.(3)In this study,70 members of the VcARF family were identified in blueberry.The identified VcARF can be similarly divided in phylogenetic tree according to the grouping characteristics of AtARF in Arabidopsis.However,combining with sequence evolution,gene structure and conservative domain analysis,it is found that the corresponding group in blueberry VcARF is unique compared with that in Arabidopsis AtARF.(4)The relative expression of key genes in graft formation was analyzed by qRT-PCR,and the graft survival rate was found to be related to PPO and PAL genes.The expressions of AUX/LAX and ARF genes in the scion during grafting were low,suggesting that the decrease of survival rate in the later stage of grafting was related to the low expression of auxin transport and response factors in the scion.