Studies On The Genetic Variation And Phylogeny Of The Native Poplars In Southwest China

In this study, the native Populus in Southwest China was used as experimentalmaterial, SRAP marker and cpDNA sequences were employed to detect genetic variationand phylogentic relationship. The aim of this study was to discuss the origin, evolution,classification, genetic variation in native Populus in Southwest, and some scientifictheoretical basis were finally proposed for future application and research of the nativePopulus resources in Southwest China.1. The results of study on621samples which came from12species in native Populus bySRAP markers were as follow:(1)338SRAP bands were amplified by7selected primer combinations, Among294makers showed polymorphism. The percentage of polymorphism is86.98%. All these dataindicated that considerable genetic variation existed among samples at DNA level.(2)1.8698alleles (Na) were detected in each locus of621samples and effectivealleles (Ne) were1.2314. The Nei’s gene diversity index and Shannon informative indexwere0.1577and0.2624respectively. Among the values of genetic diversity indexs, P.lasiocarpa (Na=1.0355、Ne=1.0218、H=0.0128、I=0.0192) were always lower than otherspecies’, but P. qamdoensis (Na=1.1929、Ne=1.1298、H=0.0810、I=0.1266) held the highestgenetic diversity indexs.(3) Among all the samples from12species, overall genetic diversity (HT) was0.1293,average genetic diversity (HS) was0.0500, coefficient of gene differentiation (GST) was0.6131and gene flow (Nm) was0.3155, while the overall genetic diversity, the averagegenetic diversity, the coefficient of gene differentiation and gene flow of all species in theSection Tacamahaca were0.1021,0.0523,0.4883and0.5241respectively.(4) The average genetic similarity coefficient of the native12Populus species was0.9091, which indicated that spcecies have high degree of similarity. The genetic similaritybetween P. davidiana and other species was lowest and ranged from0.7265～0.7914,while P. qamdoensis and P. szechuanica var. tibetica have a closest relationship and thegenetic similarity was0.9760.(5) The result of UPGMA cluster analysis showed that a close relationship existedbetween P. lasiocarpa and all species in the Section Tacamahaca, while P. davidiana wasdistinct from the other species. In the Section Tacamahaca, P. xiangchengensis, P.kangdingensis and P. schneideri clustered together; P. szechuanica and P. haoana showedmore closed affinity; P. qamdoensis and P. szechuanica var. tibetica formed a separate clade.2. Salix. matsudana was used as outgroup to research the phylogenetic relationships within80samples from34species based on8cpDNA sequences, the results showed:(1) The A+T content in cpDNA sequences was higher and there were remarkablediffenences among information from sequences. In coding regions, the length of basicsequence of rbcL-a was553.0bp, G+C content was43.3%, contained6informative sites,nucleotide diversity (π) was0.00433; the length of basic sequence of matK was848.9bp,and G+C content was32.8%, contained10informative sites but only one indels, nucleotidediversity (π) was0.00209; the length of basic sequence of rpoB was472.0bp, G+C contentwas41.9%, contained5informative sites, and nucleotide diversity (π) was0.00207; thelength of basic sequence of rpoC1was552.0bp, G+C content was42.7%, but does notcontain the informative sites, nucleotide diversity (π) was0.00046. In noncoding regions(pabA-trnH, psbI-psbK, atpF-atpH, trnL-F), the C+G content (30.2%,28.7%,28.6%,32.6%), the number of informative (10,13,6,21), the nucleotide diversity (0.00639,0.00469,0.00238,0.00441) and indels (10,10,7,24) were higher than the sequences’ incoding.(2) The distribution of interspecific and intraspecific divergences in Populus of8sequences exhibited little “barcoding gap”, and can not distinguish species independently.The identification results was different by different model. The “Best Match” and “Bestclose match” had lower the correct identifications and higher ambiguous, while the rangeof correct identifications according to “All species barcodes” was between11.25%and70.00%.(3) Based on genetic distance among interspecies and intraspecies in Populus, therewere3classes in the Section Tacamahaca. P. ussuriensis, in first class (P. trinervis, P.ussuriensis, P. cathayana and P. maximowiczii), showed more closed affinity with otherspecies. P. szechuanica var. tibetica was distinct from the other species and formed secondclass separately. Howerver, P. szechuanica var. tibetica collected from different sites weredivided into3groups, the gourp1(samples from Deiqin and Yajiang County) have a closerrelationship with the third classes of Section Tacamahaca, and the gourp2(samples fromLhasa) was distinct from the others, while the gourp3(samples from Mangkang County)was in a twilight zone between gourp1and group2. The others in the Section Tacamahacafromed the third class and showed large genetic distance with the other two classes, inwhich P. ciliate have closer relationship with others. P. gonggaensis and P. lasiocarpa in the Section Leucoides showed large genetic distance with each other and had closerrelationship with the first class and third class in the Section Tacamahaca respectively. P.davidiana and P. rotundifolia showed more closed affinity.(4) The phylogenetic relationships based on MP, Bayes and ML showed that theSection Tacamahaca could be divided into two clades. The clade1consisted of P. trinervis,P. cathayana, P. ussuriensis, P. maximowiczii and P. szechuanica var. tibetica (samplesfrom Lhasa and Mangkang County), while the others fall into clade2and existed closerrelationship with P. lasiocarpa. Section Leuce was thought to be monophyletic origin, inwhich P. davidiana and P. rotundifolia existed higher homology.