Study On Affinity Physiological Mechanisms During Rootstock Healing Of Thin-skinned Melon Grafting

In order to determine the key factors affecting the compatibility and incompatibility of thin-skinned melon’s grafting,to understand the compatibility mechanism of rootstock healing of thin-skinned melon’s grafting and to provide the theoretical reference for the popularization and application of the rootstock breeding of thin-skinned melon and the grafting cultivation on melons,this study used melon(C,Cucumis melo L.)as scion,the affinity rootstock(A,Lagenaria siceraria var.hispida.)and incompatible rootstock H(H,Lagenaria siceraria var.hispida.)screened out at the early stage of the research group as rootstocks to construct affinity rootstock combinations(C/A)using incompatible grafting combinations(C/H),self-rooted grafted seedlings(C/C,A/A,H/H)and self-injured seedlings(C,A,H)as reference.The differences and changes of histology,cytology,enzyme activity and hormone content between affinity and incompatible graft combinations of thin-skinned melons during the process of rootstock healing(1d,3d,5d and 7d)were compared.The main results were as follows:1.Paraffin sections were made at the healing sites of rootstocks at different stages after grafting of rootstocks and scions.The results showed that histological changes of affinity grafting combination C/A,self-grafting A/A and C/C were similar within 7 days after grafting:the isolation layer was formed on the first day after grafting;the isolation layer gradually disappeared on the third day after callus formation;the isolation layer basically disappeared on the fifth day;the formation of vascular bundle bridges at 7d which indicated the success of grafting;while H/H formed callus at 5th day after grafting,and vascular bundle differentiation appeared at 7th day.The isolation layer of incompatible grafting combination C/H was also formed on the first day after grafting,but the isolation layer was deep and thick,and the callus began to form on the fifth day,at the seventh day,the differentiation of vascular bundles was still not obvious since no vascular bundle bridge was formed and the isolation layer still existed.2.Studies on active oxygen metabolism and protective enzymes activity showed that the oxygen dioxide production rate,hydrogen peroxide content of affinity grafting combination(C/A),self-rooted grafted seedlings(A/A、C/C),self-injured seedlings A in scion stem(Ss)、rootstock healing site(G)and rootstock stem(Rs)were decreased gradually after grafting or treatment,however,the activities of protective enzymes such as SOD、POD、CAT and APX increased with days;the oxygen dioxide production rate,hydrogen peroxide content、SOD、POD and CAT activities in different parts of incompatible grafting combination(C/H)、self-rooted grafted seedlings(H/H)were increased with days,the activity of APX increased first and then decreased;the oxygen dioxide production rate、hydrogen peroxide content、SOD、POD and APX activities in different parts of self-injured seedlings H increased gradually as days passed,but the CAT activity increased first and then decreased.3.Detection of hormone content in different parts of different treatments showed that the contents of cytokinin(CTK)、gibberellin(GA)and Zeatin(ZT)in affinity grafting combination(C/A)、self-rooted grafted seedlings(A/A、C/C),self-injured seedlings A and C,these treatments all parts of Ss、G and R were increased gradually as days passed after grafting;affinity grafting combination(C/A)、self-rooted grafted seedlings(A/A,C/C)、self-injured seedlings A and C increased the hormone content in different parts after grafting or treatment,especially in G part;the contents of three hormones in G site of incompatible grafting combination(C/H)、self-rooted grafted seedlings(H/H)and self-injured seedlings H were decreased gradually after grafting or treatment,and the contents of three hormones were increased slowly in S and Rs sites after grafting,but the increase range was significantly smaller than that of other treatments.The content of IAA in G site of affinity grafting combination(C/A)、self-rooted grafted seedlings(A/A、C/C)、self-injured seedlings A and C were decreased gradually from the first day after grafting or treatment;the content of IAA in G site of incompatible grafting combination(C/H)、self-rooted grafted seedlings(H/H)and self-injured seedlings H were increased gradually after grafting or treatment,and the increase was obvious.In summary,the affinity grafts of thin-skinned melon quickly formed callus and differentiate within 3 days after grafting,the vascular bundle bridge can be connected and the water and nutrients can be transported and exchanged in 7 days,which may be highly related to the higher protective enzymes and growth hormones such as CTK、GA and ZT contents in the healing parts of rootstocks after grafting.However,the specific roles of protective enzymes and growth hormones in rootstock-scion compatibility of thin-skinned melon grafts still need to be studied further.