Regional characteristics in genetic variation of Ginkgo biloba, inferred from giant old trees in Japan

Abstract

Ginkgo biloba, which grows widely in Japan, was introduced from China; however, the detailed process of its spread across Japan remains unclear. Therefore, in this study, we evaluated the spread of G. biloba in Japan based on the genetic variation between giant trees from different regions. Giant trees are thought to exhibit genetic variation similar to the variation present in the early stages of introduction from China to Japan. We collected leaf samples from giant ancient trees over 8 m in girth at breast height from Kyushu to Tohoku regions. We analyzed 8 microsatellite markers in 199 samples from 180 individuals. From this analysis, we detected 8-21 alleles in 8 loci and identified 142 genotypes. Of the genotypes identified, 13 were shared by 70 individuals. We considered individuals sharing a genotype as clones. Since some individuals sharing genotypes were geographically separated from each other, it is possible that not only seeds but also cuttings were used for the propagation of G. biloba in Japan. Genetic diversity (H_E) was 0.57-0.82, while allelic richness (AR) was 4.51-8.49. We observed low H_E and AR values in eastern Japan. Therefore, G. biloba may have been transported from China to western Japan, and it is likely that a small percentage of trees further disseminated to eastern Japan.