Abstract: [Objective] Multiple-year growth traits of Eucalyptus urophylla×E. grandis F₁ hybrids were investigated, their genetic parameters were estimated, and superior hybrids and plus trees were selected aiming to provide a scientific basis for selection of mating parents and their hybrids.[Method] The F₁ hybrids of E. urophylla×E. grandis from factorial mating system were studied using the open-pollinated progenies of E. urophylla as controls. ASReml-R software was applied to assess heritability, dominance effect,additive effect, parental effect and combining abilities of growth traits when 1, 2, 4.5, 8.3 and 10.3 years old. Mean single-tree volume was calculated for each hybrid combination, and superior combinations were determined as those with volume above mean+standard deviation of all combinations. Selection of plus trees was conducted with two standards, I:mean + two times standard deviation, and Ⅱ:mean + three times standard deviation.[Result] Growth performance of hybrids was obviously better than that of open-pollinated maternal off-springs at each age. Tree height, diameter at breast height (DBH) and individual volume at each age were significantly (P<0.05 or P<0.01) different among hybrid combinations, while no significant difference was observed among blocks. Maternal variance component of each growth trait was lower than paternal variance component when one or two years old, they were equivalent to each other when 4.5 years old, while maternal variance component was higher than paternal variance component when 8.3 or 10.3 years old. With age increase, single-tree heritability (h²) generally tended to vary from middle to low, family heritability (h_F²) from high to middle to low, while additive-to-dominance variance ratio (σ_D²/σ_A²) increased for tree height and DBH. Year-year and trait-trait genetic and phenotypic correlations were significant among hybrids. The general hybridizing abilities (GHA) of U21 and G8 were the highest among maternal and paternal parents, respectively, and the specific hybridizing ability (SHA) of U21×G5 was the highest among all cross combinations when 4.5 years old. When 8.3 years old, GHA of U21 and G19 were the highest, and SHA of U2×G19 was the highest.[Conclusion] Maternal and dominance effect of each growth trait was lower than paternal and additive effect when one or two years old, respectively,maternal and paternal effect were equivalent to each other when 4.5 years old, while maternal and dominance effect was higher than paternal and additive effect when 8.3 or 10.3 years old. A total of 7 superior cross combinations, one superior maternal parent and two paternal parents were selected, and 40 and 16 elite individuals were determined according to Standards I and Ⅱ, respectively. The findings can provide reliable parent materials for a large number of artificial seed production and clones for eucalypt extension in the future.

Key words: Eucalyptus urophylla×E.grandis, factorial mating design, genetic parameters, parental selection, growth traits