Abstract：The general combining ability (GCA) and specific combining ability (SCA) of 6 selected optimum parents of Betula platyphylla Suk in a P(P-1)/2 diallel cross were estimated by analyzing two growth phenotypes of their offspring. The results showed that two phenotype were controlled by additive effect and non-additive effect simultaneously. The general combining ability of the different phenotypes of the same parent has significant difference, and the general combining ability of the same phenotype between different parents also has significant difference. Parent Q2 is the best one, M2 take second place. Moreover, the specific combining ability of the same phenotype in various cross combination and the two phenotype of the same combination also vary prominently. After investigation and statistical analysis, we found the cross 8×Q1 has the highest SCA of height and ground diameter, and the GCA of height and ground diameter were higher than SCA. The heritability of height and ground diameter were strongly heritable, suggest that they can be used for early selection.
