【目的】无性系测定对评估无性系的遗传变异和选择的遗传增益具有重要作用,但在桉树中较少开展无性系第2或更多轮伐期的测定研究。本研究旨在了解桉树无性系第2轮伐期生长性状的遗传变异,并探讨跨轮伐期选择优良无性系的有效性。【方法】以尾叶桉×细叶桉(Eucalyptus urophylla × E. tereticornis)1个杂交组合的全同胞子代扦插无性系为材料,评估第2轮伐期3.5年生生长性状的重复力(H²)以及这些生长性状间及与第1轮伐期重要性状间的表型相关(r_p)和遗传相关(r_g)。利用最佳线性无偏预测(BLUP)法估算第2轮伐期3.5年生单株材积(V_S,3.5)的育种值(BV)并选择优良无性系,进一步评估相对遗传增益(R_G)和第1轮伐期已有选择的效率(E)。【结果】第2轮伐期3.5年生7个生长性状的H²为0.29~0.48,属于低到中等程度。生长性状间r_p和r_g大多为显著正相关;第2轮伐期3.5年生与第1轮伐期8年生和15年生的生长性状间的r_p普遍较低且多数不显著,而r_g则普遍中等相关且多数达显著水平。基于第2轮伐期V_S,3.5的BV,在15%的入选率下选择41个无性系,R_G为39.1%;相较于V_S,3.5的BV选择,第1轮伐期8年生单株材积(V₈)和15年生单株材积(V₁₅)BV选择的E分别为2.8%和-2.0%,而以上两个年份的多性状指数选择的E分别为6.1%和-1.6%,基因型-理想型距离指数(MGIDI)选择的E分别为4.2%和0.8%。【结论】尾叶桉×细叶桉无性系第2轮伐期3.5年生生长受低到中等程度的遗传控制。跨轮伐期的生长性状具有相似的遗传基础。但是,表型上第1轮伐期的生长对第2轮伐期的预测准确性不高,并且第1轮伐期已有选择相较于第2轮伐期V_S,3.5的BV选择的E值极低,表明速生无性系的评估和选择需要综合不同轮伐期的生长。

【Objective】 Clonal testing plays a pivotal role in forest tree breeding programs by enabling the evaluation of genetic variation among clones and facilitating accurate estimation of genetic gain from selection, while few studies have been conducted on the second or higher rotations of clonal test in eucalypts. This study aimed to quantify the genetic variation and clonal repeatability of growth traits at 3.5 years in the second rotation of eucalypt clones, and evaluate the effectiveness of across-rotation selection strategies for identifying superior clones. 【Method】 A set of cutting rooted full sib clones derived from a controlled cross between Eucalyptus urophylla and E. tereticornis were used for estimating clonal repeatability (H²) of 3.5-year-old growth traits of the second rotation as well as trait-trait phenotypic correlation (r_p) and genetic correlation (r_g) for these growth traits compared with these important traits of the first rotation. Clonal breeding values (BV) for 3.5-year-old volume (V_S,3.5) of the second-rotation were calculated with best linear unbiased prediction (BLUP) method and then used for selection of superior clones. Relative genetic gain (R_G) and selection efficiency (E) were assessed for the selected clones and the earlier first-rotation selections as compared to the V_S3.5-based-BV selection, respectively. 【Result】 The H² estimates for seven 3.5-year-old second rotation growth traits ranged from 0.29 to 0.48, indicating low to medium magnitude. The r_p and r_g among these second rotation growth traits were usually significant and positive. The r_p values between second rotation growth traits with 8-and 15-year-old growth of the first rotation were generally low and mostly not significant, while their r_g were generally moderate and statistically significant. A total of 41 clones were selected out from the V_S,3.5-derived-BV rank at an intensity of 15%, yielding in an R_G of 39.1%. As compared to the V_S,3.5-based-BV selection, the E values of BV selection in 8- and 15-year-old volumes (V₈ and V₁₅, respectively) of the first rotation were 2.8% and -2.0%, respectively, while the E values of multi-trait selection index (SI) method at ages 8 and 15 years of the first rotation were 6.1% and -1.6%, respectively, and those of multi-trait genotype-ideotype distance index (MGIDI) selection of the two first-rotation ages were 4.2% and 0.8%, respectively. 【Conclusion】 Growth cultivars at 3.5 years in the second-rotation of E. urophylla × E. tereticornis clones was under low to medium genetic control. Across-rotation growth traits have similar genetic basis. However, growth of the first rotation shows low predictability for that of the second rotation, and selections of the first rotation exhibit very low E values as compared to the V_S,3.5-based-BV selection, implying the necessity of across-rotation evaluation and selection at least in growth traits.