Population Genetic Strueture Of Cymbidum Ensifolium From Jiangxi Based On ITS And CpDNA Molecular Markers

Orchidaceae is the most evolved specie in monocotyledon plant and endangered plants. C. ensifolium has the high ornamental and medicinal value. Geographical environment is ringed on three sides by mountains and the plant resources of C. ensifolium are extremely rich in Jiangxi province. In recent years, due to over-excavation and other reasons, the natural habitat of C. ensifolium was seriously damaged. Ribosomal ITS sequences and chloroplast DNA (cpDNA) are the important molecular markers for studying the plant phylogenetic and molecular biogeography.This research investigated the wild resources of C. ensifolium from the Dayu ridge and Jiulian mountain, Wuyi mountain, Luoxiao mountain and Jiuling mountain of Jiangxi province. On the basic of investigation this paper assessed the genetic diversity of328individuals from17C. ensifolium populations based on ITS and cpDNA molecular markers. In order to provide more reference for protection of the C. ensifolium diversity, we analysed the reproduction, genetic differentiation and gene flow of C. ensifolium, and discussed the endangered factors of C. ensifolium polulations from the perspective of conservation genetics. The main results as follows:(1) The length of ITS sequence in C. ensifolium range from646bp to656bp, the content of G+C range from67.1%to69.1%. The length of ITS1range from240bp to241bp, the length of5.8S is163bp and the length of ITS2range from243bp to252bp. The content of G+C in ITS1,5.8S and ITS2respectively range from68.5%to72.1%, from61.3%to62.0%and from69.7%to71.6%. The content of G+C is higher in each region, while the content of G+C is significantly higher in ITS1and ITS2region than in5.8S region. The ITS sequences have40variable sites and17parsimony informative sites. The length of petB-petD intergenic region in cpDNA is 569bp, the content of G+C is33.5%and this region has9variable sites and5parsimony informative sites.(2) Analysis of ITS data indicated that the206individuals from17C. ensifolium populations had10different types, and the T2was widely distributed in the lineage types. The phylogenetic tree of C. ensifolium showed that the five populations of GX1, GX3, JG1, LN1and SW1had the closest relationship. According to the ITS AMOVA results Nm=1.2148, Nm>1showed that C. ensifolium populations had the high levels of gene flow. The gene flow was enough to play a homogenizing effect to resist the effect of genetic drift, and lead to the low level of differentiation among populations.(3) Populations genetic diversity and phylogeographic analysis based on cpDNA (petB-petD) showed that the183individuals from17C. ensifolium populations were identified11different cpDNA haplotypes, the Hap3was widely distributed in the lineage haplotypes and14populations exsisted haplotype diversity. The TCS network based on cpDNA data suggest infered that Hap3was the ancestral haplotype. Through the MDA and the neutral test results showed that the wild populations of C. ensifolium had undergone expansion events. The result of HAPLONST analysis showed that Gst=0.421, Nst=0.400, UNst/Gst=-1.09<U0.05=1-96, P>0.05, and indicated that the C. ensifolium populations had not obvious phylogeographic structure. Through using the IBD analysis of genetic distance and geographical distance of17C. ensifolium populations, which displayed that the geographical distribution was not related to genetic distance (r=0.0124,p=0.5630) and revealed that the geographic isolation was not the reason of genetic variation among the C. ensifolium populations.(4) Combing the ITS and cpDNA data, we found that the genetic diversity of17C. ensifolium populations were variable. The reason was mainly related to the distribution, location and genetic variability of C. ensifolium. The genetic differentiation was relatively low among the17C. ensifolium populations, consistent with the universal breeding system as well as the pollen and seed dispersal mechanism.