Genetic structure of Quercus gilva Blume in Japan as revealed by chloroplast DNA sequences

Quercus gilva (Blume) is an evergreen oak species that is native to Japan, China, and Taiwan. Because of a long history of human impact, this species is threatened with extinction in several regions of Japan. The objective of this study was to identify the genetic structure of Q. gilva based on chloroplast DNA (cpDNA) sequencing analysis. We collected 123 samples from 25 populations in Japan, 8 samples from 1 population in China, and 46 samples from 5 populations in Taiwan. Approximately 1815 bp of cpDNA was sequenced for each of the 177 samples. Thirteen haplotypes were detected, with no cross-region distribution of haplotypes among the three geographically separated countries. There were large genetic differences among populations (G(ST) = 0.824, G'(ST) = 0.937). Six haplotypes (haplotypes 1, 2, 3, 4a, 4b, and 5) were detected in Japan; haplotype 4a was the most common, detected from 20 populations, and the other rare haplotypes, except for haplotype 4b, occurred at the edge of the species' distribution. In addition, four haplotypes (haplotypes 1, 2, 3, and 5) were quite different from the predominant haplotype (haplotype 4a), with more than four cpDNA mutations except for a mononucleotide repeat, suggesting that populations with these rare haplotypes should be conserved separately.