Stability analysis and selection of optimal Eucalyptus urophylla × E. grandis families

To analyze the stability of growth traits and the chemical properties of wood in 55 full-sib families of Eucalyptus urophylla × Eucalyptus grandis from the reciprocal recurrent selection scheme for Eucalyptus in the Congo, two trials were conducted to compare planting spacing (833 and 2500 stems ha-1). The effect of spacing at 55 months after planting was determined for height, circumference, lignin, cellulose, extractive contents, and the genetic variance component of the syringyl to guaiacyl ratio, using single and multisite linear mixed models. The families’ stability analysis was conducted by evaluating the Pi index of Lin. Results show that increased competition between trees raises the heritability of the chemical properties of wood, except for extractive content, and reduces the heritability of growth traits. Results also showed that the chemical properties of wood are relatively constant and that selection would involve a very slight drop in lignin, cellulose, and extractive content. In the case of a short rotation, plantation spacing alters the mean values of the chemical properties of wood in most families, although some remain stable in both plantation densities. For families with a low Pi index, planting spacing has very little influence on wood quality. This suggests that high-density plantations could be established with no negative impact on wood quality. The interaction between planting spacing and the effects of the main male and female primarily concerns growth traits. The interaction between planting spacing and the family effect tends to affect the chemical properties of wood.