| The rootstock could not only improve the adaptability, expand the scope of cultivation, but also influence the growth vigor, early fruiting character and fruit quality of the apple tree. Cultivation of excellent root stocks had a great significance on the production of apple. The traditional root stocks breeding of apple was mainly depended on cross breeding and natural selection. Research about mutation breeding, haploid breeding and polyploidy breeding in root stock was little reported. Materials used in this study were tetraploid of Malus zumi which were obtained by artificial induction, and diploid ones as the control. The influence of chromosome doubling on the characteristics of morphological and photosynthetic characteristics, contents of hormones, and scion varieties was studied. This would provide a new way of apple rootstock breeding. The main research results were as follows:1. Compared with diploid of Malus zumi, the tetraploid ones were more dwarf and less growth. The long, medium and short shoots numbers were decreased. The length of leaf, internode and petiole, the leaf width were all decreased, and the leaf shape index was also smaller. But leaf thickness and branch-cortex ratio were increased. The plant height of annual and biennial of the tetraploids ones were 41% and 40% of the control. The thickness of which were 72% and 58%, respectively. The growth rate and growth rate of thick degree were 15% and 42% less than the control. The numbers of long branches, medium branches and short branches, as well as the total number of branches were 2.3%, 16.3%, 8.9% and 9.2% of the control, respectively. Leaf length and width, petioles length, leaf shape index, leaf thickness and branch-cortex ratio were 77%, 89%, 63%, 87%, 1.15 and 1.3 times of the control, respectively. Lenticel area and density of the tetraploid of Malus zumi were decreases, only 62.8% of the control. The first and second lateral roots numbers were increased of 1.5 and 1.7 times of control. The number and thickness of the main root was little and small, and 56%, 75% of the control.2. Compared with the control, tetraploid ones had obvious dwarf potential. The performance was that 2 x/4 x was shorter than 2 x/2 x. Variety thickness, petioles and internode became shorter. The shape index, length and width of leaf became smaller. There was no change on the thickness of leaf. The height and thickness of the variety of 2 x/4 x was 77% and 61% of the control, respectively. The leaf length, petiole length, leaf shape index and leaf width were 95%, 89%, 94% and 1.01 times of control, respectively.The variety of 4x/4x was shorter than 4x/2x.Variety thickness became thinner and internode became shorter obviously. The length and width of leaf became smaller. There was no change on the width and thickness of leaf. The height and thickness of variety 4x/4x were 73% and 90% of control, respectively. The leaf length, petiole length and leaf shape index were 92%, 90% and 97% of the control, respectively. 4x/4 x was shorter than 2x/4x, but there was no signification difference on 4 x/2x and 2x/2x, which indicated that dwarf characters on tetraploid of Malus zumi had certain relationships with the roots shape.3. Fuji and Yueguan on the tetraploid were obviously short than that on the diploid. The growth, the leaf length, leaf width were smaller, petiole length was longer, and leaf thickness was constant. The leaf shape index of Fuji/4 x was decreasing, and YueGuan/4 x was bigger. The heights of Fuji/4 x, varieties thickness were 56% and 65% of control. The leaf length, leaf width, leaf shape index and petiole length were 87%, 93%, 93% and 1.03 times of the control, respectively. The height and thickness of YueGuan/4 x were 77% and 92% of the control. The leaf length, leaf width, leaf shape index and petiole length of YueGuan/4 x were 97%, 87%, 1.12 and 1.12 times of the control, respectively.4. Compared with diploid Malus zumi grafted on the diploid, the ones grafted on the tetraploid showed a higher photosynthetic efficiency. But stomatal conductance, intercellular co2 concentration and transpiration rate decreased. Compared with tetraploid Malus zumi grafted on the diploid, the ones grafted on the tetraploid showed a lower photosynthetic efficiency, stomatal conductance and transpiration rate. There was no change in intercellular co2 concentration. The photosynthetic efficiency of 2 x/4x combination was the highest among the four combinations, whereas the other three indexes about photosynthetic of 2x/2x combination was the highest. 5. Net photosynthetic rate on Fuji/4 x was higher than Fuji/2 x, but stomatal conductance, intercellular co2 concentration and transpiration rate were smaller. Intercellular co2 concentration in YueGuan/4 x was higher than YueGuan/2 x, but net photosynthetic rate, stomatal conductance and transpiration rate were smaller. Compared with Fuji and Yueguan on the diploid rootstock,plants on tetraploid showed a doublepeak diurnal variation curve of net photosynthetic rate,and a lower maximal photosynthetic rates, exhibiting some characters of shade plants.6. The contents of ZRs and IAA in 2x/4 x was lower than 2x/2 x, the contents of ABA and GA were higher. The ratios in IAA/ABA,GA/ABA and IAA+GA+ZRs/ABA were lower. Contents of cytokinins, gibberellic acid and auxin in lealves of 4x/4 x was lower than 4x/2x, but abscisic acid content was higher, the same situation was in branch-cortex between 4x/4 x and 4x/2x. Contents of cytokinins, gibberellic acid and abscisic acid in lealves of 4x/4x was higher than 4x/2x, but the auxin content was lower. The ratios in IAA/ABA,GA/ABA and IAA+GA+ZRs/ABA were lower.7. Contents of cytokinins, gibberellic acid, abscisic acid and auxin in the lealves of Fuji/4 x and YueGuan/4x were lower than the control. Contents of ZR and IAA, and ratio of the IAA/ABA in branch-cortex of Fuji/4 x were lower than Fuji/2x, but the contents of GA and ABA were higher. Contents of ZRs, GA, IAA in the branch-cortex of YueGuan/4x were lower than YueGuan/2 x. But the ABA content was increased and IAA/ABA ratio was decreased. Tree body was obviously reduced. |
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