Time trends of genetic parameters and genetic gains and optimum selection age for growth traits in sugi (<i>Cryptomeria japonica</i>) based on progeny tests conducted throughout Japan

Abstract

In order to provide basic information on genetic improvement potential in Cryptomeria japonica (sugi), we estimated genetic parameters, direct and indirect genetic gains and optimum selection ages for growth traits based on the data obtained from 429 progeny test sites located throughout Japan. Medians of narrow-sense heritabilites for height and diameter at breast height (DBH) were ranged in 0.289–0.445 and 0.235–0.276, respectively. The heritability of height significantly increased after the age of 15 years. On the other hand, there were no significant differences among ages in the heritability of DBH. Medians of the age-age genetic correlations were similar when the age differences of the pairs were the same, and tended to decrease as the age differences became larger for both height and DBH. The maximum efficiencies for gain per year when the target age is assumed to be 30 years were obtained at an age of 5 years in height and of 10 years in DBH, respectively. As the values at an age of 5 years in height varied greatly depending on test site, there would likely be selection errors. Thus, the early selection at 1/3 the target age is efficient in sugi.