Abstract
The genetic and environmental control of microfibril angle (MFA), the genetic correlations with other wood and growth traits, and therefore the implications for selection are poorly documented for Eucalyptus. Thus, the objectives of this study were to determine the spatial variation of the MFA, wood density (D) and stiffness (E); to determine the relationship between MFA and wood traits and finally to estimate the genetic and environmental control of wood and growth traits from clonal and progeny tests of Eucalyptus in Brazil and Congo. Conventional methods, resonance, X-ray diffraction and spectroscopy were combined to evaluate the wood properties. MFA variation accounted for 44 percent of the variation in specific modulus (E/D) of wood. The D was the prime determinant on wood stiffness and strength while the MFA played a secondary role. The heritability estimates were moderate to high for the MFA, D, E, Klason lignin (KL) and growth traits according to the spatial position and the experimental design. Genetic control of the MFA, D and E and their genetic correlations with KL and circumference of 1.3 meters of trees varied with age. The results suggest that tree with potential to grow fast are genetically more likely to produce low D and also to decrease the MFA for ensuring stiffness required for their development. Most wood properties were genetically negatively correlated with growth, although favorable genetic correlations between many wood traits were observed. Genetic and environmental correlations were sometimes of opposite signs according to the considered trait. This can be explained by the pleiotropic effect of genes and / or linkage disequilibrium. The implications of these findings for selection strategies are discussed according to the final use of Eucalyptus wood.