Population Genetic And Phylogeographic Study Of Ginkgo Biloba L. Based On CpDNA Haplotypes

Ginkgo biloba L.,often referred to as a living fossil,is a famous and widely cultivated plant.However the possible wild populations of Ginkgo are only restricted in China. Accordingly,determination of genetic diversity,population structure and glacial refugia are of crucial importance in order to understand the historical processes which Ginkgo has undergone.In this study,using chloroplast sequence variation,we analyzed the conservation genetic and phylogegraphci issues of Ginkgo biloba L.,focusing on genetic diversity,genetic structure of this vulnerable species.The main results are summarized as follows:After a preliminary survey on 21 chloroplast DNA regions,we obtained three chloroplast fragments,then amplified and sequenced these three fragments for 220 individuals of 23 populations.A total of 2508 bp and 13 variation sites were detected,which gave rise to a total of 13 cpDNA haplotypes.Nucleotide diversity and haplotype diversity are p=0.35×10^-3and h=0.219 respectively.In SW China,8 haplotypes were found with p ranging from 0.00 to 1.32×10^-3and h from 0.00 to 0.709.Four haplotypes(C,B,K,A and M)are unique to SW China.In Eastern China,4 haplotypes were found,among which 3 are unique,p=0.60×10^-3 and h=0.48.AMOVA revealed variation exist within populations.High genetic differentiation was detected(Fst=0.40442)among populations.Haplotype phylogenetic analysis and nested clade analysis revealed that two potential refugia existed during the last glaciation:the first was located in SW China(JF,WC,PX,SP,ES and QC)and the second in Eastern China, especially Mt.TM was the first time to be identified as a refuge based on molecular analysis. Neutrality test and mismatch distribution neither support any significant postglacial population expansion,but there is some short distance migration from the margine of the refugia area in Southwestern China.The occurrence of haplotype E,which was derived from the only locally distributed haplotype I in TM,might be the result of a rapid range expansion during the last interglacial periods from Eastern China.Human transplantation has definitely played an important role in the spread of Ginkgo.In order to conserve the genetic resources of G biloba,we propose that the most desirable populations for the in situ conservation are those in SW(JF,WC,PX,SP and ES).