Genetic Geography Study Of Dendrobium Nobile Based On Mitochondrial Sequence And Single-copy Nuclear Gene Sequence

Dendrobium hancokii Rolf,which belongs to genus Dendrobium of Orchidaceae,is a rare species and is widely distributed only in China.It has highly ornamental and medicinal value.There are obvious differences in the morphological characteristics,especially in the blade profile,that is,the large type and the small leaf type.In recent years,its natural populations are seriously damaged due to human overexploitation and habitat deterioration.Therefore,the study of phylogeography not only provides theoretical basis for the evolutionary study of Dendrobium,but also provides scientific basis for the utilization and protection of D.hancokii.In this current study,from 2015 to 2017,32 wild D.hancokii populations were collected from the Central-Northwest(21 populations collected from Chongqing、Hubei、Hunan、Henan、Shanxi、Gansu and Sichuan provinces)and the Southwest(11 populations collected from Guangxi、Guizhou and Yunnan provinces),which represented its entire natural habitat range.We investigated evolutionary process,dynamic history,spatial and temporal distribution and phylogenetic relationship based on mitochondrial DNA(mtDNA)and single-copy nuclear DNA(nDNA).The major foundings of the phylogeography of D.hancokii are showed below:mtDNA(ccb256 and rpl5)and nDNA(LEAFY intron 1)molecular markers were used to investigate its phylogeography from 32 natural populations.A total of 30 mtDNA haplotypes and 36 nDNA ribotypes were identified.High level of haplotype/ribotype diversity(mtDNA:Hd = 0.954;nDNA:Rd = 0.966),total genetic diversity(mtDNA:HT=0.953;nDNA:HT=0.975),and significant population phylogeographic structure(mtDNA:NST 0.8777>GST 0.358,P<0.05;nDNA:NST 0.853>Gsr＝0.325,P<0.05)were detected within D.hancokii populations.IBD analysis showed that there was a correlation between the genetic distance and the geographical distance ofD.hancokii,but it did not exist in neighboring populations.Mismatch distributions and neutral test indicated that all sampled populations in China expanded their range around 0.31 Ma based on nDNA analysis,whereas mismatch distributions and neutral test of mtDNA data refused population expansion model.The results based on mtDNA and nDNA were not congruent,different events happened in evolutionary history.Network based on the mtDNA haplotypes and nDNA ribotypes showed all haplotypes/ribotypes could be divided into two groups(Groupl and Group2).Group 1 could be divided into two clades(Clade A and Clade B).Group2 could be divide into two clades(Clade C and Clade D).There was no shared haplotype or ribotype between the large leaf type and the small leaf type(Groupl and Group2),implying D.hancokii populations might have evolved allopatrically.Based on the obtained mtDNA and nDNA results,we inferred that the D.hancokii originated from Wuling Mountains.And that,the central and southwest regions of China are the centers of diversity of D.hancokii.