Across-rotation genetic analysis and multi-trait selection in a cloned cross of Eucalyptus urophylla × E. tereticornis

Jiahong XuMingming ZhouQijie WenMei Li^*Siming Gan^*

• Research Institute of Tropical Forestry, Chinese Academy of Forestry, Guangzhou, China

Clonal testing is crucial for genetic parameter estimation and elite clone selection of elite clones. However, few studies have been carried out the testing clones over two or more rotations. In this study, a clonal trial of the sibs of an E. urophylla  E. tereticornis cross was used for genetic parameter analyseis and multi-trait selection on such trait types as across-rotation growth, wood properties of the first rotation, coppicing ability, and coppice chlorophyll fluorescence. Clonal repeatability (H 2 ) estimates for the growth traits in of the first-rotation ranged from 0.73 (diameter at breast height at age 15) to 0.84 (single-tree volume at age 2.5) and were more or lessgenerally higher than those of growth traits in of the second-rotation (0.11-0.62). H 2 of coppicing and chlorophyll fluorescence traits were 0.35-0.57 and 0.03-0.53, respectively, revealing low to medium genetic control of these traits. Phenotypic correlations ( ) and additive genetic correlations ( ) were usually high between growth traits within a single rotation and between coppicing traits, but varied largely with other trait pairs. In pParticularly, the final (2.5-year-old) volume of the second rotation volume at 2.5 years had a very weak but moderate positive with earlier-stage volumes of the first rotation. Multi-trait selection index (SI) and multi-trait genotype-idiotype distance index (MGIDI) methods were performed at an intensity of 15% under four scenarios each combining two to , three, four, or five traits. Relative genetic gain (RG) and selection efficiency (E) estimates were positive for all the traits involved in multi-trait selection, indicating the usefulness of all the selection scenarios. As compared to SI, MGIDI method showed somewhat lower RG and E in 8-and 15-year-old volumes but higher RG and E in 8-year-old wood basic density and cellulose content of the first rotation. This study can have important implications for eucalypt clonal breeding and management, including the necessity of across-rotation investigation, evaluation of method option for multi-trait selection options, early selection ages, and the possible use of seedling deployment population.