Genetic Relationships Among Poplar Species In Section Tacamahaca Spach From Western Sichuan Of China

Although western Sichuan is regarded as a natural distribution and variation center forthe Section Tacahamaca of the Populus species in China, little is currently known about themajority of poplar species occurring in this region. In the present study, molecular data wereutilized to determine the genetic relationships among Populus species in Section Tacamahacain western Sichuan including P.cathayana, P. prezewalskii, P. yunnanensis, P. kangdingensis,P.schneideri, P.simonii and P.trinervis. The results are as fellows:1. The genetic variation at SSR and ISSR loci was abundant. All the 10 SSR loci werepolymorphic, and the number of alleles per locus varied from 5 to 17 with a mean valueequaling 11.9. Based on the 11 ISSR primers, 130 clear and reproducible DNA fragmentswere generated, of which 119 (91.5ï¼…) were polymorphic. Our results reveal that single SSRlocus can present more genetic information, while more polymorphic bands can be detectedby single ISSR primer. Moreover, the genetic distance, cluster and PCA analysisdemonstrated that: a close relationship among accessions of the same species and suggestedmonophyly in P. przewalskii and P. cathayana; P. schneideri is genetically highly similar to P.kangdingensis; P. trinervis and P.simonii have a close genetic affinity; P.yunnanensis isdistinct from the other species.2. Genetic relationships of poplar species in Section Tacamahaca from western Sichuan were evaluated by means of AFLP and TE-AFLP. For four AFLP primer combinations, atotal of 284 bands were obtained of which 200 (70.4ï¼…) were polymorphic with the average of50 polymorphic bands. For four TE-AFLP primer combinations, a total of 192 band wereobtained of which 139 (72.4ï¼…) were polymorphic with the average of 34.7 polymorphicbands. Our results indicate that the genetic information of AFLP is similar to that ofTE-AFLP, and little less than that of ISSR, but only about 1/3 of that of SSR. However, theability of information detection of the two AFLP-based markers is much higher than that ofISSR and SSR. In addition, the cluster analysis of AFLP, TE-AFLP and combined data revealthat: P.yunnanensis, P. trinervis and P. simonii clustered together, and P.trinervis and P.simonii showed more closed affinity; the other four poplar species clustered together, P.cathayana and P. schneideri showed more closed origin especially.3. The cpSSR analysis for seven Populus species belonging to the Section Tacamahaca.Four out of the seven analyzed chloroplast loci were polymorphic, whereas none of the lociwere polymorphic across the accessions within a species. 13 bands and 4 different kinds ofhaplotypes were reduced. Based on 5 pairs of cpDNA primers, 73 fragments (52 polymorphic)and 9 kinds of haplotypes were produced. However, none of the polymorphic was detected bythe 5 mtDNA primer pairs, revealing conservation of mtDNA region. The cluster analysis ofcpDNA revealed that: similar matemal phylogeny among P. yunnanensis, P. trinervis and P.simonii; the other four species clustered together, P. schneideri and P. kangdingensis showedmore closed maternal lineage especially.4. Our molecular data, morphological characters and nature habitat revealed that: sameto the traditional taxonomy assignment, genetic variation within a same Populus species islower than that among PopuIus species in Section Tacamahaca; P. yunnanensis may share itschloroplast ancestor with P. trinervis and P. simonii; moreover, sister genetic relationship of P.trinervis and P. simonii indicated their similar origin; P. schneideri clustered with P.kangdingensis and P. cathayana, respectively, and may have derived from an ancienthybridization event involving the ancestors of the two species.