Genetic Variation Of Hybrid Clones Between Populus Deltoides Bartr. And P. Ussuriensis Kom.

Poplar is an important forest species in China and other countries, and is the major tree species for industrial timber and ecological protection; therefore genetic improvement of poplar is very important. In this study,27 hybrid clones between P. deltoides and P. ussuriensis which were obtained through artificial hybridization and seedling selection were used as material, propagated and established a filed test stand in Pingquan county of Hebei province in 2006. Then, the growth traits were measured every year from 2006 to 2010, and phenotypic traits, photosynthetic and cold-resistant physiological traits were determined. Meanwhile, one-year-old cuttings of clones were exposed to different low-temperature treatment, and then physiological and biochemical indices were determined. Genetic variation of growth traits, phenotypic traits, photosynthetic and cold-resistant physiology in 27 hybrid clones between Populus deltoides and P. ussuriensis were analyzed, and clones' fingerprints figure was draw using AFLP markers. The main results were as follows:1. Significant difference (P<0.01) were found among clones and years in growth traits, coefficient of variation of growth traits in the consecutive 5 years is from 1.57 to 21.82, and repeatability were above 0.620. Further analysis of multiple comparisons, correlation coefficient and growth trends for the consecutive 5 years'growth traits, significant positive difference (P<0.05) were exhibited between a total of 14 hybrid clones including 135,136,141,146,147,153,163,177,181,183,190,191,192,193 and P.×beijingensis on growth traits.2. Significant difference (P<0.01) were found among different clones in 21 phenotypic traits of hybrid clones. The range of coefficient of variation of phenotypic traits were 3.30～19.17, and repeatability were 0.558～0.989. Principal component analysis of clones were did by using 21 phenotypic traits, based on the principle of cumulative contribution rate were greater than 85%, the two principal components were selected, which the first principal component mainly means comprehensive factors of "crown height, crown width, length of lateral branch and leaf area", the second principal component mainly means the factor of "teeth of leaf margin", based on this, two-dimensional ordination diagram were draw, and 28 clones were divided into two groups.3. There were significant difference (P<0.01) between clones in 17 photosynthetic physiological indices such as the net photosynthetic rate etc. of hybrid clones. The coefficient of variation of indices were 0.64～10.84, and the repeatability were 0.843～0.998. The further study found that a total of 7 clones including 146 and so on had higher value of Pn, etc. than the control P.×beijingensis, and there were significant difference between them. The diurnal curve of Pn, Tr, Gs in clones exhibited bimodal trends, with high values at 10:00 and 16:00, and the values of 10:00 were greater than 16:00; while diurnal varieties of Ci exhibited "V"-shaped curve, with the lowest point at 14:00; the Pn of the hybrid clones increased with the increase of light intensity in light saturation curve, and the Pn maintain the same maximum when the light intensity reached saturation.4. There were significant difference (P<0.01) existed in different clones in eight physiological indices of hybrid clones before and after low temperature treatment. The coefficient of variation of indices were 3.05-10.48, and the repeatability were 0.738-0.991. The indices values increased significantly after low temperature stress, and clone 146,147,183,190,191,192 and 193 were deduced more cold-resistance. The indices values of clones increased with variety degrees when they exposed to 10℃and 5℃24 h, whereas the all indices values except MDA content gradually reduced when the temperature dropped to 0℃,-5℃, -10℃and -15℃. Under the consecutive 5℃stress, the soluble protein, MDA content and CAT, APX, GR activities increased immediately after 3 h, the soluble sugar content and SOD, POD activities reduced slightly at the beginning of stress, subsequently increased with fluctuation, and then decreased gradually.5.12 hybrid clones were analyzed using primer combinations of Mse I+2/EcoR I+3 by adopting AFLP marker technology.10 primer combinations with more amplification bands were selected from 32 primer combinations, and polymorphism level of those primer combinations were from 23.5% to 41.6%. The results of UPGMA cluster analysis and pedigree relations of 12 clones were the same, which indicated that clones with the same parents had higher similarity coefficient. The fingerprint figure of 12 hybrid clones were draw using 9 polymorphism bands from 6 primer combinations, which would provide bases of identification and protection for hybrid clones.The results revealed the genetic variation of growth traits, phenotypic traits, photosynthetic and cold-resistant physiology of 27 hybrid clones between P. deltoides and P. ussuriensis, and using those results to evaluate hybrid clones comprehensively, then seven clones were selected with excellent performance of growth, phenotype and cold-resistance; meanwhile, fingerprints figure of 12 hybrid clones including those excellent clones was draw using AFLP markers, which laid a foundation for further choose of excellent clones and authorization and protection for new varieties. In addition, the change of physiological and biochemical indices of hybrid clones under different time and low temperature stress were studied, which provided a theoretical reference for further studying the physiological mechanism of cold-resistance of poplar indeed forest tress.