Study On Genetic Diversity And Origin Of Populus Tomentosa Carr.

Populus tomentosa Carr., being a native poplar species in China, has played a key role in timber production and ecological environment construction along the Yellow River. It is mainly distributed in the vast area of northern China, and occupied about one million km~2. Consequently, population of P. tomentosa is probably abundant in genetic variation. Diversity and genetic differentiation in P. tomentosa were detected from phenotype, allozyme and DNA level in this study. The tested materials were sampled from national genebank of P. tomentosa in Guanxian County, Shandong Province. All clones, which comprised the national genebank, were selected and collected from nine provinces (municipality) of Shannxi, Shanxi, Henan, Hebei, Shandong, Gansu, Anhui, Jiangsu and Beijing. Additionally, the origin of P. tomentosa was explored by means of AFLP markers for nDNA and multiple alignment of trnL-trnF sequences for cpDNA. By these experiments, the obtained major results and conclusions are described as follows.1. The variation of phenotypic characteristics was profusion. Analyses of variation for all measured characteristics were significantly different among populations and among clones within population. The phenotypic differentiation coefficient Vst was 0.1974, phenotypic diversity index was 0.055 among populations and 0.596 within population, Shannon's information index was 0.075 among populations and 1.007 within population. These results indicated that the variation within population was greater than between population's, and the genetic variation of clones within population was the main sources of genetic diversity in P. tomentosa. According to the result of cluster based on several phenotypic diversity indices, nine provenances may be divided into two groups.2. Allozymes inheritance and variation of 9 enzyme systems were studied using horizontal starch-gel electrophoresis among 227 clones of P. tomentosa. 15 loci were presented, of 13 loci were polymorphic. The percentage of polymorphic loci was 86.67%. Average number was 2.2 alleles and 1.989 effective alleles on per locus. The expected heterozygosity was 0.453, and Shannon's information index was 0.682. At population level, the estimates were P=86.67%, A=2.178, Ae=1.942, He=0.442, I=0.662. The fixation index was smaller, F=-0.5868, and genetic differentiation coefficient was not high, Fst= 0.0274. However, the higher genetic variation on allozymes was showed that much more heterozygotes were contained in population, and only 2.74% variation was among populations. The UPGMA cluster, which based on Nei's genetic distance, illustrated thatnine provenances were distributed in three groups.3. Nine primer combinations were selected and used for evaluating genetic diversity of P. tomentosa using AFLP markers. 712 AFLP markers were observed, among them, 464 markers were polymorphic, P=65.17%. At species level, A=1 .991, Ae=1 .479, Nei's gene diversity index (77) was 0.289, 7=0.445. The value of diversity parameters at population level was P=60.49%, A=1.605, Ae=1.479, H=0.289, 7=0.445. The genetic differentiation coefficient was 0.2477. It indicated that 75.23% variabilities occurred in population of P. tomentosa. Nine provenances of P. tomentosa were divided into two groups by the dendrogram constructed using Nei's genetic distance.4. The relationship among fourteen clones of P. tomentosa and P. bolleana, P. adenopoda, P. alba, P. hopeiensis and P. davidiana were analyzed at nDNA level by AFLP markers using nine pairs primers selected from thirty four primer combinations. The statistical results showed that 464 markers were polymorphic among 712 AFLP markers, and the maximal genetic identity and the minimal genetic distance were found between P. tomentosa and P. adenopoda. The phylogenetic dendrogram also illustrated that the relationship between P. tomentosa and P. adenopoda was closer than that between P. tomentosa and other four putative parents. Thus, it can be concluded from this study result that P. adenopoda was likely to be a parent of present P. tomentosa.5. T...