Studies On The Genetic Variation Of Large Old Poplars In Section Tacamahaca Spach From Southwest China

Southwest China is regarded as one of the natural distribution and evolution centres for Populus species. There exist a great number of large old poplar resources with diameters above 1 m and age more than 100 years, which are distributed around the temple, four sides! and the boundary of mountains. It is of great importance to study the genetic variation, phylogenetic relationship, determine the taxonomic status and resistance of poplars, but the basic research on large old poplars is relatively little. In the present study, molecular data analyzed by SSR, AFLP were utilized to determine the genetic variations among Populus species in Section Tacamahaca southwest China including P. szechuanica, P. kangdingensis, P. xiangchengensis, P. schneideri, P. szechuanica var. tibetica, P. haoana and P. qamdoensis. These scientific theoretical basis were finally proposed for future application and protection of the large old poplar resources in Southwest China. 1. SSR markers were used to study the DNA of large old poplars, and the results were as follows:(1) A total of 80 fragments were returned by 7 primers and the number of polymorphic bands was 80. The percentage of polymorphic bands was 100%, and the average percentage of polymorphic bands of 7 large old poplars were ranged from 30.00 % to 48.75 %, with the average of 42.68 %; The number of effective alleles(Ne), Nei#s genetic diversity(H) and Shannon#s information index(I) varied from 1.1360 to 1.1935, 0.0825 to 0.1230 and 0.1285 to 0.1934, with the average of 1.1621, 0.1037, 0.1656, respectively. The coefficient of genetic differentiation(Gst) among populations of 5 different large old poplars changed from 0.1281 to 0.5596, and the gene flow(Nm) varied from 0.3934 to 3.4041, which indicated that the genetic variation mainly existed in different individuals within populations, and there existed some gene exchanges among populations.(2) The average genetic similarity coefficient of large old poplars was 0.9490, the highest similarity coefficient was 0.9715 between P. szechuanica and P. kangdingensis; P. xiangchengensis and P. schneideri, P. szechuanica var. tibetica and P. haoana had the same similarity(0.9696). Both cluster analysis and principle coordinate analysis revealed that there had close genetic relationships between P. szechuanica and P. kangdingensis, P. xiangchengensis and P. schneideri, P. szechuanica var. tibetica and P. haoana. 2. After the study on the sample of large old poplars by AFLP marks, we draw the following results:(1) Among the 226 samples, 7 fluoresence labeling AFLP primers were used to amplify the genomic DNA. 592 AFLP bands were obtained, and 488 of them were polymorphic bands and the percent of polymorphic bands was 82.43%. The average percentage of polymorphic bands of 7 large old poplars was ranged from 67.91 % to 80.41 %, with the average of 72.16 %; The number of effective alleles(Ne), Nei#s genetic diversity(H) and Shannon#s information index(I) varied from 1.5420 to 1.6474, 0.2965 to 0.3528 and 0.4253 to 0.5055, respectively. The coefficient of genetic differentiation(Gst) among populations of 5 different large old poplars changed from 0.0924 to 0.2096, and the gene flow(Nm) varied from 1.8857 to 4.9135, which showed that the genetic variation mainly existed in different individuals within population, and there existed some gene exchanges among populations.(2) The average genetic similarity coefficient between species was 0.9366, and the P. szechuanica var. tibetica and P. haoana had the highest similarity(0.9644), the similarity coefficient between P. xiangchengensis and P. schneideri was 0.9513. Both cluster analysis and principle coordinate analysis revealed that P. xiangchengensis and P. schneideri, P. szechuanica var. tibetica and P. haoana had closer relationships. 3. Combined the both markers to analyze the genetic variation of large old poplars, we draw the following conclusions:(1) Combined the data of SSR and AFLP, the average percentage of polymorphic bands of 7 large old poplars ranged from 63.99 % to 76.64 %, with the average of 72.18 %; The number of effective alleles(Ne) varied from 1.4495 to 1.5903, with the average of 1.5410, and the average of Nei#s genetic diversity(H) was 0.2996; Shannon#s information index(I) changed from 0.3963 to 0.4668. The coefficient of genetic differentiation(Gst) among populations of 5 different large old poplars changed from 0.0939 to 0.2300, and the gene flow(Nm) varied from 1.6739 to 4.8255, which indicated that the genetic variation mainly existed in different individuals within populations, and there existed some gene exchanges among populations. The correlation between SSR, AFLP and combine markers indicated that the correlation between AFLP and combined markers matrices was higher, while lower was scored between SSR and AFLP alone.(2) Correlation detection and analysis of SSR, AFLP and combined markers indicated that the correlation between the combination of markers and AFLP was the highest, while the the correlation between SSR and AFLP was the lowest.(3) The average genetic similarity coefficient between species analyzed by combine data was 0.9395, P. szechuanica var. tibetica and P. haoana had the highest similarity(0.9652), the similarity coefficient between P. xiangchengensis and P. schneideri was 0.9540. Both cluster analysis and principle coordinate analysis indicated that P. xiangchengensis and P. schneideri, P. szechuanica var. tibetica and P. haoana had closer relationships. 4. Comparison of genetic diversity between large old trees and seedlings:SSR, AFLP and combine data all indicated that large old trees and seedlings had the higher genetic diversity. AFLP and combine data showed that the genetic diversity of seedlings were higher than large old trees, while the large old trees expressed higher genetic diversity analyzed by SSR.