Objective  To study the genetic variation of Eucalyptus urophylla, select excellent clones suitable for growing in Yangjiang, and provide a scientific basis for selection and promotion of new clones.

Method  Totally 76 E. urophylla clones were used as materials, and the clonal test fields of E. urophylla were constructed in three times. After afforestation, tree height and diameter at breast height (DBH) were measured every year, and the phenotypic traits were analyzed by variance analysis and genetic parameter estimation. The multi-trait genotype value was used to screen excellent clones, and the genetic gain of excellent clones was also estimated.

Result  Tree height and DBH of E. urophylla had significant differences among clones, and the variation coefficient of growth traits decreased year by year. Except for the traits of a few years, the variance component of E. urophylla growth traits reached a significant or extremely significant level among blocks, with genetic variance components ranging from 0.10 to 22.61, environmental variance components ranging from 0.18 to 45.86, and repeatability ranging from 0.10 to 0.42, respectively. There was strong positive genetic correlation between tree height and DBH except for tree height of one-year-old tree. Both genetic and phenotypic correlations between tree height and DBH reached medium to high levels with the correlation coefficients ranging from 0.40 to 0.98. The correlations between tree height and DBH at the same tree age were large. Based on the predicted tree height and DBH genotype values at different ages with the growth performance, excellent clones of ZQUB29, ZQUA34, ZQUC33, ZQUA15 and ZQUA33 had higher growth genotype and phenotype values at all ages, indicating that these clones may be more stable throughout the rotation period and were excellent clones.

Conclusion  The growth differences among E. urophylla clones involved in the fields are extremely significant, and five excellent clones can be used as the basic materials for the subsequent genetic improvement of E. urophylla and the breeding of improved varieties.