| Cross breeding is the most important method to breed new poplar varieties. This study used different poplar species and hybrid clones as parent materials, saving the immature embryos by artificial pollination and tissue culture in order to get hybrid population bred by Populus tomentosa. This study also analyzed the heights and diameters at breast height of trees aged from two to four years in four sites, and these trees included 29 poplar hybrid clones and one selected clone (LM50) by previous cross breeding during seedling test. Genetic stabilities of these clones were also evaluated. Comprehensive evaluation of 30 poplar hybrid clones was made by analyzing growth characters, photosynthesis and antioxidant system. Fingerprint mapping of hybrid clones was established by SSR specific amplification analysis. The results were as follows:1.19 cross combinations were selected from 17 parent materials to form cross experiment among species and hybrid clones in Leuce. By analyzing flower buds length and width of crossing parents, we found that there was significantly difference of flower anthotaxys length and width between individuals. The range of male plants flower anthotaxys length was between 44.40 and 126.43mm, and the range of width was between 11.29 and 15.73mm, while the ranges of female plant were from 13.84 to 25.48mm, and from 5.01 to 7.30mm respectively. The hybridization compatibility and the amount of seeds were high when using P. alba×P. glandulosa and P. tomentosa×P. bolleana as hybrid parents. The clusters of clones with P. tomentosa as hybrid parent were easily to shed when young embryos were immature.420 P. tomentosa hybrid progenies from 6 cross combinations were produced by tissue culture. The result of analyzing seedling height and ground diameter of 2-year offspring showed that there was significant difference of seedling height and ground diameter among different cross combinations. The average seedling height was from 49.67 to 84.42cm and the average ground diameter was between 5.61 and 10.86mm. The variation coefficient of height in the same cross combination was from 13.66% to 45.32%, and that of ground diameter was between 13.03% and 39.51%, and these results provided evidence for clone selection during seedling.2.29 superior clones and one poplar selected clone (LM50) were chosen as test materials, and field experiments were set in randomized blocks. By investigating growth characters of 4-year young plantation, we found that the heights, diameters at breast height and volumns of 30 poplar hybrid clones were significantly different among different sites, clones and interaction of clones and sites. The range of phenotypic variation coefficient was between 19.84% and 69.04%, and the range of genetic variation coefficient was from 14.65% to 62.59%. The proportion of genetic variation coefficient in phenotypic variation coefficient increased every year, indicating that the variation was caused mainly by genetic fators. The repeatabilities of heights, diameters at breast height and volumns of 30 poplar hybrid clones increased by the ages of trees, and the repeatabilities of each factor during 4 years were between 0.8887 and 0.9902. The correlation analysis of poplar heights, diameters at breast height and volumns showed that the phenotypic variation coefficient of diameters at breast height between one-year and four-year poplars was up to 0.8075, and that the genetic variation coefficient was 0.8841. While the phenotypic variation coefficient of diameters at breast height between three-year and four-year poplars was 0.9838 and with genetic variation coefficient 0.9979. Phenotypic variation coefficient and genetic variation coefficient could provide theoretical basis for clone selection. The adaptability analysis of poplar clones at different sites showed that clones of BL28, BL87, BL69, BL101 and BL103 had wide adaptation and made no difference planting in 4 sites. While the other clones showed particular regional adaptabilities at different sites.3. By comprehensively evaluating 17 indices in 30 poplar hybrid clones in Fengfeng mining area in Handan, Hebei Province, we found that these indices among different hybrid clones were extremely significantly different (P<0.01). The range of phenotypic variation coefficient of hybrid clones was between 15.63% and 57.50%, and the range of genetic variation coefficient was from 8.99%to 52.57%. The repeatabilities of each factor were between 0.7734 and 0.9849, showing that there was ample genetic diversity in poplar clones and the variation was highly controled by genes, and this result can provide basis for clone selection. We used principal component analysis to divide 14 indices of poplar clones into 3 principal components, and the first principal component was biomass characters such as height and diameter at breast height, the second was stem form characters such as stem straightness and distance between leaves, the third was leaves characters such as leaf length, width and leaf area. The result of principal component analysis showed that principal component values Y1 of clones BL106, BL107, BL23, BL46, BL78 and BL83 were positive and high, and indicated that the biomass such as height, ground diameter, diameter at breast height, volumn and crown width were high; while principal component values Y2 of clones BL104, BL106, BL107, BL28, BL69 and BL85 were high, revealing that the straightness, distance between branch, and branching degree of clones were high, and the principal component values Y3 of clones BL106, LM50, BL104, BL107, BL98 and BL49 were higher and showed the length, width and area of leaves of these clones were higher.4. The results of photosynthetic indices of 30 poplar hybrid clones showed that the diurnal variations of net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) were classified as double-peak curves, while diurnal intercellular CO2 concentration (Ci) decreased at first and then increased. Pn-Par response curves and Pn-Ca response curves were classified as S-curve, the light saturation points (lsp) were between 1396.55 and 1469.86μmolm-2s-1, and light compensation points (lcp) were between 33.08 and 81.17μmolm-2s-1. CO2 saturation points (csp) were between 974.03 and 1080.50μmol CO2 mol-1, and CO2 compensation points (ccp) ranged from 74.03 to 93.35μmol CO2 mol-1. The difference of instantaneous photosynthetic indices among 30 poplar hybrid clones was extremely significant (P<0.01), and the average Pn, Gs, Ci and Tr were 19.82μmol·m-2·s-1, 0.37 mol·m-2·s-1,263.68μmol·mol-1 and 4.38 mol·m-2·s-1 respectively. Photosynthetic indices, Pn,Gs,Tr were significantly positively related to the height and diameter at breast heigh of trees, indicating that photosynthetic indices had great effect on growth of clones.5. Study on the monthly dynamic variation of contents of chlorophyll, MDA and activities of POD and SOD of poplar clones showed that trend of chlorophyll contents was low-high-low. The average malondialdehyde (MDA) kept increasing, while peroxidase (POD) and superoxide dismutase (SOD) increased at first and then decreased. Correlation analysis showed that POD,SOD and chlorophyll content were significantly positively related to biomass, while MDA content was significantly negtively correlated to biomass. We evaluated the pre-resistance of different clones by cluster analysis and classified the 30 hybrid clones into 3 groups, and the first group had high enzyme activity, revealing their most strong resistance and would be vulnerable by stress. The second group had stronger resistance, and the third group with low resistance would be susceptible to stress.6.30 poplar hybrid clones were specifically amplified by using 16 pairs of SSR primers, and 40 DNA specific bands were obtained, the numbers of DNA bands which were amplified by each pair of primers were from 2 to 6 and the average number of bands was 2.5, and the DNA bands were between 100-600bp. The range of genetic distance among 30 poplar clones was from 0.0864 to 0.2716, with an average distance of 0.1436. Fingerprinting map of hybrid clones was established with DNA bands, and the result showed that there was close genetic relationship among poplar hybrid clones.In present study, biomass, stem form, photosynthetic indices and antioxidant system were used to comprehensively evaluate poplar hybrid clones. Meanwhile, fingerprinting map was also established for the evaluation. All these provided the valuable theoretical basis for superior hybrid clones selection. |
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