Genetic diversity and structure of seed pools in an old planted Pinus thunbergii population and seed collection strategy for gene preservation

To achieve gene preservation in tree populations when planting seedlings to regenerate forests, specific and practical guidelines and criteria for seed collection are needed to ensure reliable coverage and effective capture of the current genetic variation. We examined the genetic variation of adult trees (524 trees) and seed pools (1618 seeds) collected from 70 mother trees in an old planted population of Pinus thunbergii in Japan using seven nuclear microsatellite markers. To consider a suitable seed collection strategy, we monitored changes in allelic diversity of seed pools with an increasing number of mother trees and examined the required number of mother trees. We found significantly higher allelic diversity statistics in seed pools of mother trees with smaller diameter at breast height. Spatial genetic autocorrelation analysis showed significantly positive kinship coefficients between both pairs of adult trees and seeds collected from mother trees for up to 100-m distance classes. Based on the rarefaction curve, seed pools obtained from approximately up to 30 mother trees could cover and saturate most of the genetic diversity and composition of the adult tree population and the potential overall seed pools, particularly for statistics that are less likely affected by rare alleles. Indications from the mother tree number, together with considerations for the size or spatial distribution of mother trees, are expected to contribute not only to guidelines for in situ genetic management of local planted populations, but also to the development of strategies for ex situ gene preservation of populations as genetic resources.