Genetic Evaluation and Combined Selection for the Simultaneous Improvement of Growth and Wood Properties in Catalpa bungei Clones

Catalpa bungei is an important timber tree. Improvements in growth and wood quality are important goals of C. bungei breeding, and it is necessary to understand the genetic parameters of specific target traits and genetic correlation between growth traits and wood properties for tree breeding. In this study, the genetic parameters of height, diameter at breast height (DBH) and wood properties were estimated and genetic and phenotypic correlations between growth traits and wood properties were evaluated in C. bungei. Finally, different selection scenarios were used to evaluate and select optimal clones. The results showed that there were significant differences in growth and wood properties among clones. The wood hardness (0.66–0.79), basic density (0.89), air-dried density (0.89) and compression strength parallel to the grain of wood (CSP) (0.84) had high repeatability. The variance component proportions indicated that the variation in wood properties came mainly from different genotypes (clones) rather than from different individuals of the same clone. The DBH showed a significant negative genetic correlation with the hardness of radial section (HRS) (−643), basic density (−0.531) and air-dry density (−0.495). This unfavorable relationship makes it difficult to improve growth and wood quality simultaneously in C. bungei. We selected the optimal clones under different scenarios, and we obtained 7.75–9.06% genetic gains for growth in the scenario in which height and DBH were the target traits. Genetic gains of 7.43–14.94% were obtained for wood properties by selecting optimal clones in the scenario in which wood properties were the target traits. Approximately 5% and 4% genetic gains were obtained for growth and wood properties, respectively, for the combined selection. This study provides new insights into the genetic improvement of wood quality in C. bungei.