Effects of clonal selection by microfibril angle on the genetic improvement of stiffness in Cryptomeria japonica D.!Don

The microfibril angle (MFA) of latewood tracheids and its radial variation at breast height in Cryptomeria japonica D. Don (sugi) were investigated with twelve clones collected from three sites in the Kyushu region, Japan. Large variations both between clones and between sites were observed. The MFAs were well correlated to the stiffness of the logs collected from the sample trees. A simulation of clonal selection according to the ranking of the clones in MFA demonstrated that the log stiffness of the selected population was much improved even when the selection relied on MFAs in the second ring from the pith. The improvement in log stiffness by MFA selection was not different from the selection by log stiffness itself. The results indicate that early selection by MFA is very effective in improving log stiffness in this species.