Selection Of Dwarfing Stocks And The Dwarfing Mechanism For Cornus Wilsoniana

In this paper, stock seedlings and grafted plants from10excellent clones of Cornus wilsoniana were studied. By means of field investigation, morphological and anatomical structure observation, physiochemical indicators detection and so on, the growth trend, net photosynthetic rate, the main endogenous phytohormones and the enzymes(POD, IOD) content of leaves were measured; the correlations between anatomical structure, major physiochemical characteristics and plant vegetative growth were analyzed separately; the integrated system of indexes for the dwarf resource selection was set up by the method of principal component analysis and the dwarf stocks were chosen primarily; the primarily chosen dwarf stocks and vigorous stocks were analyzed by the method of expression spectrum difference analysis; the genes, the basis and the adjustment of molecuLar biology that were related with dwarf growth were explored. Compared the differences of grafted plants with the same scion and the different stock in the growth vigor, the morphological structure, the main endogenous phytohormones and the enzymes(POD, IOD) content of leaves, discussed the mechanism of impacts of stocks on the dwarf growth of grafting seedlings, in order to provide the theoretical basis of the selection of excellent dwarf stocks and the cuLtivation of grafting seedlings. The research resuLts were as follows:1There were difference among rootstocks of different clones in the growth vigor and the morphological structure. The growth vigor was closely related with the morphological structure.There were great differences among rootstocks of different clones in the growth vigor. G1was the shortest, and G22was the tallest. There were significant correlations among the height, the ground diameter, the leaves area and the length of internodes. The indexes of vegetative growth were able to directly and totally show the vegetative growth vigor of plants.The transverse section areas, the ratios of phloem area to xylem area and the density of trachea of rootstocks of10clones were different. The ratio of phloem area to transverse section area was negatively related with the height, the ground diameter and the area of leaves, so as to the xylem area and the ratio of phloem area to xylem area to the length of internodes. The transverse section area, xylem area and the density of trachea were positively related with height, the ground diameter area of leaves. The correlation coefficient between the density of trachea and the height was so significant that couLd be the prediction index of the pre-screening dwarf stocks of Cornus wilsoniana.There were some difference among the transverse section area of stem, the area and ratios of various tissues of neuter rootstocks. The correlation coefficient between the area of meduLla or phloem and the length of internodes were so significant that couLd be the prediction index of the pre-screening dwarf stocks of Cornus wilsoniana, but the correlation between the xylem area and stocks vegetative growth vigor was not significant.Of the leaves anatomical structures, the thickness of both upper and lower epidermis, the spongy tissue thickness and the palisade tissue thickness had significantly positive correlations. The thickness of palisade tissue to the total thickness of leaf and the ratio of palisade tissue thickness to spongy tissue thickness were both negative related with the length of internodes significantly. Both of them couLd be one of the supplementary prediction indexes of dwarf stocks.2There were great differences among rootstocks of different clones in the photosynthetic physiology. The photosynthetic physiological indexes were closely related with the plant vegetative growth.There were great differences among rootstocks of different clones in the photosynthetic physiology. The photosynthetic rate and the transpiration rate of G1were the lowest, and G22with the highest photosynthetic rate, G18with the highest transpiration rate. The photosynthetic rate had significantly positive correlation with the length of stomas, the density of stomas and the content of chlorophyll a, which also had significantly negative correlation with the intercelluLar concentration of carbon dioxide. The transpiration rate had significantly positive correlation with the density of stomas. The photosynthetic rate had significantly positive correlation with the height of the plant, and the conductance of stoma, the density of stoma, the content of chlorophyll a also had significantly positive correlation with the height of the plant and the ground diameter. The intercelluLar concentration of carbon dioxide had significantly negative correlation with the height of the plant and the leaves area, and both coefficients were0.722and0.790. In terms of all the above correlation, the photosynthetic rate, the density of stomas, the conductance of stomas, the intercelluLar concentration of carbon dioxide and the content of chlorophyll a couLd be considered as the prediction indexes of dwarf stocks of Cornus wilsoniana.3There were differences among rootstock leaves of different clones in the enzyme activity of (IOD, POD) and the content of endogenous phytohormones (IAA、GA、ABA、 ZR), which were also closely related with the plant vegetative growth. The physiochemical indexes include the reducing sugar/the soluble sugar, the activity of IOD and POD, the content of endogenous phytohormones and so on were different among different clones. The reducing sugar/the soluble sugar had negative correlation with IOD, POD, ZR, meanwhile had positive correlation with the content of IAA、ABA、GA. The content of IOD had negative correlation with the content of IAA, GA, however had significantly positive correlation with the content of POD. The content of POD had positive correlation with the content of IAA, ABA, ZR, also had negative correlation with the content of GA. The content of POD had significantly negative correlation with the height of the plant and extremely significantly negative correlation with the ground diameter; The value of IAA+GA+ZR/ABA was positively related with the height, the ground diameter and the leaves area. Therefore, POD and IAA+GA+ZR/ABA couLd be considered as the prediction indexes of dwarf stocks of Cornus wilsoniana.4Analyze the prediction indexes of the primarily chosen dwarf resource by the method of main component analysis and set up the integrated system of indexes for the dwarf resource. Analyze the15morphological, photosynthetic physiochemical indexes of Cornus wilsoniana by the method of principal component analysis. Set up the score expression of5main component factors and the integrated system of indexes for the dwarf resource. The integrated model was calcuLated by weight of the ratio of the eigenvalue of each principal component to the total eigenvalue of all the main components.F=0.152×the ground diameter+0.209×leaves area+0.194×the density of trachea+0.134×the phloem area+0.050×the meduLla area-0.056×the palisade tissue+0.080×the spongy tissue-0.074×the ratio of the palisade tissue to the spongy tissue+0.084xthe photosynthetic rate+0.159xthe conductance of stoma-0.093×the intercelluLar concentration of carbon dioxide+0.161×the density of stomas+0.232xchlorophyll a%-0.097×POD+0.143×(IAA+GA+ZR/ABA).The sequence of the plant growth trends of different clones which were valued by the integrated model was as below:G22>G9>G15>G36>G34>G18>G19>G12> G20>G1. G1had the lowest growth vigor and the highest dwarf extent, however G22had the highest growth vigor and the lowest dwarf extent. The predictions of the integrated system and the real measured values of the height of the plants were the same on the whole. The5principal component of all the10clones of Cornus wilsoniana couLd be systematically clustered that all the10clones of Cornus wilsoniana were able to be separated into3types:the first type included G1、G20、G12、 G18、G34、G19and the characteristics of those were the weak the ground diameter, the short height of the plant, the small the ground diameter and the small leaves area; the second type included G15、G36、G9and the characteristic of those was mainly the relatively strong growth trend; the third type included G22and the characteristics of it were the strong growth trend, the tall height of the plant, the large ground diameter, the large leaves area and so on.5Identify the major genes closely related with the dwarf of Cornus wilsoniana by the method of expression spectrum difference analysis on the dwarf stocks and the vigorous stocks.By means of digital expressive gene library, and compared with the reference genome of mixed clones, among the dwarfing rootstock G1and tall building rootstock G22, there were2010difference expressive genes, of which651genes were up reguLation expressive gene, and the rest were down reguLation express。Between the G1and G22, there were104difference expressive genes that related to dwarfing plant. Of which, most genes involved in photosynthesis, redox reaction, glycometabolism and composing of ribonucleo-protein. Genes related with photosynthesis mostly encode the key enzyme in the process of photosystem Ⅱ, thylakoid protein and binding protein of chlorophyll.Genes encoding protein for rhamnose and polysaccharide (include pectin, soluble starch, celluLose and hemicelluLose) biosynthesis were lower level expressive in G1than that in G22. That meant the readjustment of Glycometabolism was the main factor of dwarfing plants for dogwood6There were significant differences of grafted plants with the same scion and the different stock in the growth vigor, the morphological structure, meanwhile the growth vigor of grafting seedlings and stocks were the same on the whole.There were differences among the anatomical structures of the roots, stems and leaves of grafted plants, which also had correlation with the anatomical structures of the roots, stems and leaves of stocks to some extent. The increment of root growth of the grafted stock was smaller than the seedling stock, however the relative proportion of various tissues of the root was similar between the grafting stock and the seeding stock. There were significantly positive correlations between the root of grafting stock and the root of the seeding stock in the xylem relative area, the phloem relative area and the ratio of the xylem relative area to the phloem relative area. There were little correlation between the morphological structures of stem of grafting seedlings and the morphological structures of stem of stocks. There were significantly positive correlations between the morphological structures of leaf of grafting seedlings and the morphological structures of leaf of stocks.There were differences between the leaves of grafted plants and the leaves of stocks in the content of main endogenous phytohormones and the enzymes (POD, IOD). The contents of IOD, IAA and GA of the grafted plant leaves were obviously lower than those of the stock leaves; however the contents of ABA and ZA of the grafted plant leaves were obviously higher than those of the stock leaves. The correlation between the content of IAA of stocks and the content of IOD of grafted plants was extremely significant positive, and the correlation coefficient was0.807. Meanwhile, the content of IAA of stocks had significant negative correlation with the content of ZA of grafted plants.The traverse section area and the xylem area of the root of grafted plants had positive correlation with the activity of POD of the leaf, however had negative correlation with the content of IAA and GA.Among the grafted plants of Cornus wilsoniana, the structures of the root, the stem and the leaf were transformed by the stock, so as to the activity of IOD and POD and the content of endogenous phytohormones. As the resuLt, the stocks were able to adjust the growth and transform the structure of the plant, finally dwarf the plant.