The origin and genetic variability of vegetatively propagated clones identified from old planted trees and plantations of Thujopsis dolabrata var. hondae in Ishikawa Prefecture, Japan

摘要

Clonal plantations of Thujopsis dolabrata var. hondae have been established in Ishikawa Prefecture, Japan, since at least the 1800s. Historical planting of the species has led to the development of vegetatively propagated local cultivars, which originated from 'donor' trees that have often been conserved in sacred groves or avenues at shrines and temples. These donor trees must have been selected from natural populations. In this study, we estimated the origin and genetic variability of clones identified among old planted trees and clonal plantations of T. dolabrata var. hondae, using 19 microsatellite markers. We discovered 12 clones among old planted trees, including 5 identical to members of a set of 14 we previously identified in plantations (giving 21 clones in total). Based on analyses combining assignment and exclusion tests, we inferred origins of 8 of those 21 clones: 6 may have originated from a natural population distributed in Ishikawa, 1 from Hokkaido and Aomori, and the other from Iwate and Yamagata, suggesting the clones constituting cultivars have multiple origins. The clones identified in plantations have significantly lower genetic variability and higher relatedness, indicating that clones of cultivars have a much narrower genetic base than those of natural populations. We suggest new clones selected from natural populations elsewhere, as well as Ishikawa, are needed for future breeding of T. dolabrata var. hondae to develop clonal forestry for this species.