Objective To estimate the genetic parameters for wood properties of Eucalyptus urophylla (U) and E. camaldulensis (C) F₁ hybrids and provide a theoretical basis for the selection of parental genotypes and mating design for the improvement on wood properties of eucalypts.

Method A trial involving 36 reciprocal crosses from six C parents and six U parents preselected for superior growth and stem straightness was built. Ten open-pollinated (OP) half-sib families using the hybrid parents as females were included as the controls. The wood basic density (BD), fibre length (FL), fibre width (FW) and FL/FW at age 9 were assessed with 2 average stand trees from every 5 tree plot, 984 wood cores were drilled for 82 combinations with 6 repeatations, at the height of 1.3 meters along the north to south. Specific combining ability, heterosis, single tree's narrow-sense heritability (h²) for female and male, genetic and phenotypic correlation coefficient were estimated for four wood property traits by ASReml-R.

Result Inter-specific hybrids generally performed better than the OP progenies in terms of BD, which showed a significant heterosis. Female C by male U crosses (C×U) generally outperformed those involving female U by male C (U×C) in terms of BD, whilst, U×C crosses generally outperformed those C×U in terms of FL, FW and FL/FW. The maternal effects of wood basic density, fibre length and FL/FW were lower than paternal effects in U×C crosses, whilst the maternal effects of four wood properties were higher than paternal effects in C×U crosses. The h² estimates based on general hybridizing ability for BD and fibre traits were generally middle to low. Except for FL/FW, the dominance variance of all the other three wood properties were larger than additive variance. The ratio of hybrid dominance to additive variance (σ_D²/σ_A²) were larger than 1 for BD, FL and FW. The trait-trait genetic correlations amongst hybrids were significant and negative between BD and FW, significant and positive between BD and FL/FW, whilst, not significant and negative between BD and FL, and significant and positive between FL and FW. However, The trait-trait phenotypic correlations between wood properties were significant and positive except that between FW and FL/FW.

Conclusion Genetic parameters of U and C hybrids in terms of wood properties are different from parental genotypes and mating direction, and inter-specific hybrid breeding and forward reciprocal selection is feasible for the improvement of wood properties.