Glacial refugia of Ginkgo biloba and human impact on its genetic diversity: evidence from chloroplast DNA.

Variations in the trnK region of chloroplast DNA were investigated in the present study using polymerase chain reaction-restriction fragment length polymorphism to detect the genetic structure and to infer the possible glacial refugia of Ginkgo biloba L. in China. In total, 220 individuals from 12 populations in China and three populations outside China were analyzed, representing the largest number of populations studied by molecular markers to date. Nineteen haplotypes were produced and haplotype A was found in all populations. Populations in south-western China, including WC, JF, PX, and SP, contained 14 of the 19 haplotypes and their genetic diversity ranged from 0.771 4 to 0.867 6. The TM population from China also showed a high genetic diversity (H = 0.848 5). Most of the genetic variation existed within populations and the differentiation among populations was low (G(ST) = 0.2). According to haplotype distribution and the historical record, we suggest that populations of G. biloba have been subjected to extensive human impact, which has compounded our attempt to infer glacial refugia for Ginkgo. Nevertheless, the present results suggest that the center of genetic diversity of Ginkgo is mainly in south-western China and in situ conservation is needed to protect and preserve the genetic resources.