Age Trends in Genetic Parameters and Genetic Gains of Growth Traits in Multiple Progeny Test Sites of Hinoki Cypress (chamaecyparis Obtusa)

Growth data obtained from Chamaecyparis obtusa growing at 28 progeny test sites in the Kanto breeding region of Japan were analyzed to estimate the genetic parameters and genetic gains. Specifically, the data were used to estimate stem diameter at breast height (DBH), tree height (TH), and stem volume in order to assess the feasibility of breeding, and differences in genetic parameters and genetic gains associated with growth traits based on age and climatic conditions were clarified. The median values of narrow-sense heritability for DBH and TH across all ages ranged from 0.229 to 0.263 and from 0.201 to 0.433, respectively. Based on the efficiency of improvement (genetic gain per year), it appears that the most efficient selection for DBH and stem volume would be at one-third of the improvement target age (set to 30 years in the present study). We analyzed the variation of narrow-sense heritability and age trends of those among three groups of test sites exposed to different climatic conditions. Age and group x age interaction were shown to have significant effects on the narrow-sense heritability of TH and volume and that of DBH and volume, respectively. However, no significant effects of group x age interaction were detected on the efficiencies for gain per year of all traits, implying that this parameter might not be affected by climate conditions. Therefore, it was suggested that early selection is possible with almost equal efficiency in all climate groups.