Genetic analysis distinguished new natural population and old plantations of Cryptomeria japonica

Abstract

Natural forest is important not only for conserving genetic diversity, but also as a future breeding resource, especially for forestry tree species. Cryptomeria japonica is an important forestry tree species in Japan, but natural populations are limited. We discovered apparently natural C. japonica individuals on Mt Aoba, adjacent to Wakasa Bay in Fukui Prefecture, Japan. The area around Wakasa Bay was an important refugia for this species during the Last Glacial Maximum. To clarify whether these individuals are natural origin or not, we sampled 195 individuals with a diameter at breast height (dbh) greater than 60 cm (with an average dbh of 79 cm), and conducted genetic analyses with 249 SNP and 20 SSR markers. We found two genetic clusters identified as ura-sugi and omote-sugi lineages and the genetic diversity of the sample was similar to known natural populations. The ura-sugi lineage showed a clear correlation between age and dbh, whereas the omote-sugi lineage showed no correlation. The ura-sugi lineage was also genetically very similar to nearby natural populations. Most of the omote-sugi lineage trees were about 100 years old regardless of dbh, and located in one small valley close to a village. The results suggest that the ura-sugi lineage (124 individuals) represents a population of natural origin, whereas the omote-sugi lineage (60 individuals) population was probably planted about 100 years ago using trees of non-local origin. Seven individuals appeared to be hybrids, displaying both ura-sugi and omote-sugi lineages. In situ conservation of the ura-sugi individuals should be a priority, after removing the omote-sugi lineage, in order to conserve the natural genetic resources they represent. Ex-situ conservation strategies should also be implemented to protect the endemic gene pool from gene flow from the many C. japonica plantations in the surrounding area.