【目的】研究桉树无性系的遗传变异,选育适用于中大径材培育的桉树优良无性系,作为后续良种选育的基础。【方法】以12年生尾细桉(Eucalyptus urophylla × E. tereticornis)杂种无性系试验林的154个无性系为研究材料,结合12年间调查的生长性状和8年生时测定的材性性状,进行方差分析、相关性分析及遗传参数估算等,最后采用主成分分析法进行多性状综合选择。【结果】不同无性系间的生长和材性性状差异均达显著水平,即通过选择可提升培育尾细桉成优质大径材的潜力。中大径材尾细桉无性系开展早期选择的时间在4.5~6.5 a最适,生长性状对基本密度的间接选择效果均为正向,以树高最佳。各性状的无性系重复力为56.28%~85.34%,单株重复力为24.35%~59.27%,无性系重复力均大于单株重复力,各性状受较高的遗传调控,遗传稳定性高。定选的10个优良无性系的生长性状遗传增益为14.64%~73.89%。【结论】所选12年生尾细桉杂种无性系满足桉树中径材培育要求,具有培育成大径材的潜力。

【Objective】Eucalyptus species are widely planted in south China because of their large trunk diameter, superior growth and desirable wood properties.Because of their shorter cultivation period and high economic benefits, cultivating Eucalyptus trees with large trunk diameters can effectively increase the supply of medium/large diameter timber, which is in high demandin China. However, the research on Eucalyptus cultivation in China has started recently, and most of this research focused on the forest management and silvicultural technology ofEucalyptus. The number of studies on high-quality breeding and selection is currently low, and only a few Eucalyptus species used for plantations have been investigated.In this study, we investigated the genetic variation of Eucalyptus clones with the goal of selecting superior clones with medium/large diameter timber and providing the basis for further breeding selection.【Method】In this research, the growth traits of 154 twelve-year-old hybrid clones of E. urophylla×E. tereticornis were investigated, in an experimental plantation in Gonghe Town, Heshan City, Guangdong Province. Wood properties,such as basic density, cellulose content, hemicellulose content, lignin content, lignin syringyl-to-guaiacyl ratio, and fiber length-to-width ratio of eight-year-old plants were also analyzed. Genetic analyses of growth traits and wood properties included the analysis of variance and correlation and the analysis of genetic parameters. Principal component analysis was performed in order to classify the investigated hybrid clones, and comprehensive multiple trait selection was applied for the medium/large diameter timber.【Result】① The differences among the growth traits and wood properties of different clones were significant, increasing the potential for screening high-quality large diameter timber clones ofE. urophylla×E. tereticornis. ② Selection of medium/large diameter timber hybrid clones of E. urophylla×E. tereticornis was not recommended at the early stage because of the low correlation results of growth traits between plants in earlier and later stages. The optimal selection time was from 4.5 to 6.5 years and this was better than selection after 1-3 years because using selection in the early stages,it is possible to exclude some important varieties too early. ③ The effect of growth traits to select wood basic density was positive, and the effect of height was the highest in the indirect trait selection experiment. ④ We observed that the clonal repeat ability of all traits was greater than that of an individual, with the clona land individual repeat ability results of 56.28%-85.34% and 24.35%-59.27%. The traits of the clones were genetically stable and were highly regulated by their genetic background. ⑤ The hybrid clones ofE. urophylla×E. tereticornis were classified into four groups by the principal component analysis. Ten superior clones were selected with the selection rate of 6% and their genetic gain of growth traits was 14.64%-73.89%. The results showed that average height, diameter, volume and basic density of the 487 clones were 27.5 m, 27.6 cm, 0.719 7 m³ and 0.529 3 g/cm³, respectively.【Conclusion】The results of the cultivation experiment of E. urophylla×E. tereticornis hybrid clones showed that the clones had an appropriate medium diameter timber and had the potential for cultivation as a large diameter timber tree. The ten selected superior clones could be utilized in plantation areas similar to the ones in this study with the goal of the production of large diameter timber. This production could be achieved under the following environmental conditions: thick soil layer, loose and fertile soil, and sufficient water and heat. This study was based on only 154 clones of a single hybrid, and further research is needed to clonal selection. Future studies should consider combining genetic linkage maps, QTL mapping, and using clones from more hybrids and locations in order to analyze the complex genetic background explaining the growth traits and wood properties of E. urophylla×E.tereticornis hybrid clones.