Genetic Diversity And Phylogenic Relationship Of E.nutans Populations In Eastern Qinghai-Tibetan Plateau

E.nutans is an important species of genus Elymus L.of the tribe Triticeae in the Poaceae family which is also the dominant species in Plateau and meadow.It is widely distributed in Northwestern China,especially in the Qinghai-Tibet Plateau.It has been researched more because of excellent resistance genes which can provide good gene resources for tribe Triticeae and improve forage quality.In this experiment,we selected E.nutans populations in 16 regions of Eastern Qinghai-Tibet Plateau,and based on the chloroplast DNA rp132-trnL sequence,matK sequence and trnL-F sequence,we discussed their genetic diversity and genetic relationship among these populations.The results were as below:(1)Based on cpDNA rp132-trnL sequences showed the genetic distance of E.nutans populations ranged:0.304-0.869,The smallest genetic distance was between Hualong County population,Zeku County population and Gonghe County population(0.125),followed by Hualong County population and Zeku County population(0.336),The genetic distance between Tongde County population and other populations was large awalys(0.819-0.869).Chengduo County population(S=15,h=4,Hd=0.998),Qingshuihe County population(S=163 h=7,Hd=0.995),Yushu County population(S=16,h=5,Hd=0.876),Gangcha County population(S=10,h=9,Hd=0.978),Haiyan County population(S=11、h=5、Hd=0.933)have the higher genetic diversity.Except for the Delingha County population(P<0.01),Wulan County population(P<0.05)and Haiyan County population(P<0.05),most of the populations experienced population expansion.Analysis of molecular variance showed that within-population variance was described as 96.36%of the total variance while among-population variance was 3.64%,which meant that within-population variance was the main resource of genetic variation of E.nutans in Eastern Qinghai-Tibetan Plateau.The fixation index(Fst)was 0.0369 and number of migrants(Nm)was 13.85 based on the Gst-values,which meant that gene flow was very frequent among different geographical populations.Principal coordinates analysis showed that among Zeku County population,Gonghe County population had a further relationship beween other populations,followed by Tongde County population.No correlation was found between the geographic distance and genetic distance(r=-0.090,P=0.140).Combining MP tree and NJ tree,we found that the population of Delingha County,Dulan County,Gonghe County and Yushu County could gathered together always in the phylogenetic trees,and the node is close to the root of the phylogenetic trees.It indicated that the above four populations were closely related than others,so were the population of Haiyan County and Gangcha County.(2)Based on cpDNA matK sequences showed the range of genetic distance between various poplations is 0.038-0.172,The existing data analysis showed that genetic distances in Yushu Tibetan Autonomous Prefecture populations(0.038-0.116)between other populations in Eastern Qinghai-Tibetan Plateau was small,while the Tongde County population(0.097-0.172)and Gangcha County population(0.109-0.172)were much larger than others.The Chengduo County population(S=10,h=3,Hd=0.932),Qingshuihe County(S=9,h=6;Hd=0.999),Yushu County population(S=9,h=6,Hd=0.991),Gangcha County population(S=9,h=4,Hd=0.996),Haiyan County population(S=8,h=4,Hd=0.959)had higher genetic diversity.The Hualong County population,Tongren County population(P<0.05),Zeku County population,Maduo County population,Yushu County population(P<0.01),Wulan County population and Tianjun County population all experienced population expansion.Analysis of molecular variance showed that among-population variance was 2.81%which meant that within-population variance was the main resource of genetic variation of E.nutans in Eastern Qinghai-Tibetan Plateau.The fixation index(Fst)was 0.02816 and number of migrants(Nm)was 12.78 based on the Gst-values,which meant that gene flow was very frequent among different geographical populations.Principal coordinates analysis showed that Tongde County population and Gangcha County population had a further relationship beween other populations.No correlation was found between the genetic distance and geographic distance(r=-0.206,P=0.070).Combined with MP tree and NJ tree,we found that Yushu County population and Qingshuihe County population and Tianjun County population could gather together in both two trees as well as have closely genetic relationship usually.(3)Analyzing a small amount of tmL-F gene sequence data of 12 existing populations,the results showed that the genetic distance of various populations was 0.0001-0.7741.Between the three populations of Tongde County,Yushu County and Dulan County,the genetic distances were the smallest.Mantel analysis showed that there was a significant negative correlation between geographic distance and genetic distance(r=-0.234,P=0.02).Combined with three chloroplast genes datas,the genetic diversity of E.nutans population in Yushu Tibetan Autonomous Prefecture was the highest where had a suitable habitat owned more opportunities to store genetic information.Analysis of molecular variance(AMOVA)showed that genetic variation mainly existed within populations in Eastern Qinghai-Tibet Plateau,and genetic differentiation among populations was low.Principal coordinates analysis showed similar results with genetic distance and phylogenetic trees.Mantel results showed that there was no significant relationship between genetic distance and geographical distance(P<0.05).Moreover,the populations of Yushu Tibetan Autonomous Prefecture and Haibei Tibetan Autonomous Prefecture could always gather together in the phylogenetic trees which indicates a closer relationship.The results showed that cpDNA noncoding region was more suitable as a marker for genetic diversity and phylogeny in this study.