Objective To evaluate the reliability of Resistograph penetration method on indirect measurement of wood density of Eucalyptus urophylla×E. tereticornis hybrids, detect the parental effects on cross phenotypic traits and the correlations between growth and wood density, and select fast-growing and high wood-quality Eucalyptus urophylla×E. tereticornis hybrids.

Method In a 7.5-year-old trial stand with fifty six hybrid combinations derived from an incomplete factorial mating among 10 E.urophylla (female) and 10 E.tereticornis(male) parents, 79 trees were sampled to determine the correlation in wood density between volumetric and Resistograph measurements. The effects of parents on hybrid growth and wood density were detected by variance analysis. Multiple comparison and independent selection were performed to make joint selection of stand volume and wood density.

Result The phenotypic and genetic correlation coefficients between volumetric and Resistograph measurements were 0.52 (P < 0.001) and 0.55 (P < 0.05), respectively. The differences in the traits of height, DBH and stock volume, were highly significant (P < 0.001 or 0.01) among either females or males, but no significant difference was observed for female×male interactions. For ResistograPh-based wood density, however, the differences were highly significant (P < 0.001) among the males and significant (P < 0.05) for female×male interactions, but insignificant among the females. The growth traits of height, DBH and stock volume were highly significantly correlated in both phenotypic and genetic terms (P < 0.001), while their phenotypic and genetic correlations with wood density were highly significant (P < 0.001) and insignificant, respectively. A total of 14 hybrids and 17 individual trees were selected out.

Conclusion Resistograph method is convenient, economic and reliable for indirect measurement of wood density of E. urophylla×E. tereticornis hybrids. Female and male parents selecting and parental pairing are important for breeding fast-grow and high wood-quality hybrids. Since there is no significant genetic correlation between growth and wood density, it indicates the necessity of selecting separately against the two traits. The hybrids and trees selected out are of valuable plant materials for further cultivating fast-grow and high wood-quality eucalypt hybrids.