Trends in additive, dominance and environmental effects with age for growth traits in Eucalyptus hybrid populations

Abstract

Expression of additive and dominance effects during development of forest trees species is poorly documented. A set of 10 subpopulations, generated from factorial mating amongst subsets of 88 females and 107 males representing 684 families and 37,206 individual trees, was used to estimate variance components between 4 and 65 months in a Eucalyptus urophylla * grandis breeding population. The variance components were significantly different from zero for female, male and female-by-male interaction effects for height and circumference. The results, from the set of experiments, stressed the huge dispersion of variance component estimates among subpopulations. The trends were modelled using linear and nonlinear models. The trends in additive, dominance and environmental variances with age showed three phases corresponding to the stage of competition during stand development. No significant trend was observed for the coefficients of variation of these three effects. The dominance to additive variance ratio did not show specific age-related trends and was close to 1.2 during the growth period. The additive, dominance and environmental correlations between height and circumference were higher than 0.8 after 24 months. A similar age-related trend was observed for the additive and dominance effects. These results emphasise the significant role of dominance in the genetic control of growth traits. They differ from the majority of studies of pines, where additive variance is preponderant, but are similar to those of other eucalyptus studies. In the context of Congolese breeding strategy, this can be explained by the phenotypic selection of parents constituting the breeding population and/or the expression of overdominance in eucalyptus hybrid populations planted in marginal zones.