Preliminary Investigation On DNA Barcoding And Molecular Phylogeny Of Populus L. Species In China

Populus species are one of the most common tree species in northern China. The strictly outcrossing and extensive interspecific hybridization among the Populus species made the traditional morphological classification difficult to differentiate species. DNA barcoding is a rapid species identification method that is achieved by a standard DNA fragment. It uses the genetic material DNA as an identifying characteristic, so its application on Populus species identification will help to quickly identify and promote the protection of wild germplasm resoyrces.This study of DNA barcoding choosed 17 species 69 samples representing Chinese Populus, which selected nuclear gene fragments ITS, DSH10, DSH28 and chloroplast fragments matK, ndhF, ycf1, atpH-atpl, the results showed that species distinguishing ability of nuclear gene DSH10, DSH28 and ITS species were significantly better than chloroplast fragments for single or multi fragments combinations. The nuclear gene fragments combination ITS+DSH10+DSH28 had the highest resolution 47.06%(Tree-building method, containing P. euphrantica, P. tomentosa, P. davidiana, P. maximowiczii, P. pseudomaximowiczii, P. rotundifolia, P. lasiocarpa, P. trinervis), which showed that the nuclear gene fragments was more suitable for the identification of Populus species. The highest resolution fragments’ could not distinguish half of the species, so we needed improve it from the research methods. This study we recommended the special tiered DNA barcoding system to identify species from group level to species level, which in group level we could use nuclear gene fragments such as ITS, DSH28 and in species level we could use SNPs technology.Then we amplificated and sequenced 20 Populus species of single copy nuclear gene fragments DSH10 and DSH22 and 21 of ITS fragments(of which 13 species were from the barcoding study). Combining the data found in GeneBank of DSH10, DSH22, ITS, matK and trnU-psbA, we made the phylogenetic analysis for Chinese Populus species. Results showed that section Turanga were the base group of Populus, section Populus were a monophyletic group. Species P. pseudoglauca should belong to the section Tacamahaca form the phylogenetic tree of nuclear and chloroplast genes. Genetic relationship of section Leucoides, section Aigeiros and section Tacamahaca is closer, section Aigeiros and section Tacamahaca tended to cooccupy the end of phylogenetic tree and had the closest relationship. The phylogenetic analysis of chloroplast gene and nuclear gene showed that section Aigeiros and section Tacamahaca was likely to be hybrid origin. According to the geographic distribution of each species and phylogenetic tree constructed above, we initially identified seven groups:section Turanga group; section Leucoides group; section Populus group; section Aigeiros group; northeast Tacamahaca group; southwest Tacamahaca group 1; southwest Tacamahaca group 2, which will contribute to DNAbarcoding research and database establishment of Chinese Populus species.