Study On Phylogenetic And Genetic Relationships Of The Native Popμlus In Sichuan

Poplar is the general designation of Populus species of Salicaceae. Populus species is one of the oldest genus with millions of years of history, which contains about 100 species. Poplar is widely planted world around, especially in Europe, North America and Asia. China has abundant genetic resources of poplar, especially in southwest of China, there are plentiful poplar species and endemic rarities. Poplar mainly distributed in western Sichuan and south-east of Qinghai-Tibet Plateau, the unique historical factors and ecological conditions of this area make it is rich in poplar species and variation types. Thereby, Sichuan is considered as a variation center of poplar. However, the study on the systematic classification of Populus in this region was mainly focused on the morphology. Although there were some new understandings at the molecular level in recent years, there still existed many doubts and differences on the classification system of poplar species and evolution relations between species. In the study, the genetic relationships of 17 Sichuan native poplar species from the sections of Populus, Tacamahaca and Leucoides were investigated by using AFLP molecular marker and sequence analysis of the trnT-F region of cpDNA. The results were as follows.(1) In the study, the method of modified CTAB was used to extract DNA from poplar for AFLP analysis. The result of agarose gel electrophoresis testing indicated that the DNA banding patterns were clear and complete, degradation and RNA contamination phenomenon was not obvious. This method could extract poplar genomic DNA easily, quickly and efficiently. The results showed that the modified CTAB method was suitable for AFLP analysis of poplar, while it was not suitable for the amplification of trnT-F region of cpDNA. However, the traditional CTAB method was suitable for sequence analyse of the trnT-F region of cpDNA.(2)Ten pairs of primer combinations were screened out from 64 pairs of AFLP primer combinations were used for the final selective amplification. The results showed that 585 genetic sites were amplified, including 505 polymorphic sites, and polymorphism rate was 86.32%. Different primer combination produced different numbers of bands ranging from 45(M48/E57) to 78(M48/E41). Each primer combination could obtain 58.5 bands in average, with 50.5 polymorphic bands.(3) Three trnT-F regions (IGS1, Intron, IGS2) of cpDNA were amplified with the universal primers. The length of amplified bands were different among 17 poplar species, ranging from 1461 to 1503bp with the average of 1482.4bp. The base frequencies was also different between different species, which contained A (40.3%-40.9%,40.6% in average), G(15.8%-16.4%,16.3% in average), C(14.3%-14.6%,14.4% in average), and T(28.5%-28.7%,28.7% in average). The content of G+C was ranging from 30.3(P. xiangchengensis) to 30.8(P. schneideri, P. purdomii,P. lasiocarpa, and P. adenopoda), and with average of 30.7%.(4) The result of AFLP cluster analysis among sections in the study was consistent with the classically morphologic taxonomy. The sequence analysis of trnT-F region of cpDNA could not effectively distinguish the genetic relationship of these species, probably because the information sites in trnT-F region of cpDNA of poplar were overplus. Combined with morphology, analysis of AFLP and the sequence of trnT-F of cpDNA, the results showed that P. pseudoglauca belonged to the selection of Tacamahaca; P. schneideri might be a nature hybrid of P. kangdingensis and P. cathayana. It was not appropriate that P. schneideri was regarded as a variety of P. kangdingensis in the existing classification system. There was close genetic relationship between P. trinervis and P. simonii, and their may be derived from the same species. P. gonggaensis may be the cross of Leucoides and P. cathayana or P. schneideri of Tacamahaca, but it was still doubtful that whether P. gonggaensis could be regarded as a separate species or not because of its narrow distribution area. While it was determined that P.yunanensis was one parent of Luding poplar which was a natural hybrid species, its other parent may be P. lancifolia. Butuo poplar had obvious characteristics of Leucoides, and the results of AFLP analysis also indicated that it had close genetic relationship with P. gonggaensis and P. lasiocarpa. However, the further researches should be carried out to identify their were same species or varieties.