Viabilidade da seleção precoce de progênies de Eucalyptus dunnii Maiden

Abstract

The Eucalyptus genus has great commercial importance in the forestry sector worldwide. Brazil stands out worldwide as one of the largest pulp producers, being this the main consumer in the sector of wood planted. The rotation time is one of critical factors in genetic breeding programs for forestry species. An alternative to reduce the rotation time would be using the early selection. Thus, this study aims to evaluate the efficiency of the early selection of Eucalyptus dunnii progenies. We used data from experiments of progeny test, implanted in

two locations (Site 1 e Site 2) relied in complete randomized blocks, using progenies of half- sibs. In site 1, 21 progenies were evaluated with 20 repetitions and a plot of a single plant, and

in site 2, 33 progenies were evaluated with 10 repetitions and a linear plot of five plants. For both experiments, the traits, diameter at breast height and total tree height were measured and the mean annual increment in volume was estimated. For each experiment all traits were evaluated at juvenile age (Site 1: 39 months and Site 2: 30 months) and at rotational age (Site 1: 61 months and Site 2: 50 months). The variance components were obtained using the restricted maximum likelihood method and best unbiased linear prediction. In addition, covariances were estimated, to obtain the phenotypic (rF̂ ) and genotypic (rĜ ) correlations and correlated responses (RC) between progenies and trait for juvenile and rotation ages. To determine the viability of applying selection, the selection of 30% of the progenies at each age, for each trait, was simulated, obtaining estimates of genetic gains through direct and indirect selection. The results revealed that the (rĜ ) estimates were of a higher magnitude than the (rF̂ ) for both experiments. For both experiments, the RCjj' responses efficiency estimates were high for diameter at breast height (Site 1: 95% and Site 2: 97.19%) and mean annual increment (Site 1: 93.15% and Site 2: 93.15%) in relation to in total height (Site 1: 83% and Site 2: 85.28) in direct gain. The RCjj' of indirect gains were similar to direct gains for diameter at breast height and mean annual increment and lower for height. It was evident that the precocious selection was efficient in the selection of Eucalyptus dunnii half-sib progenies, in both applied methodologies, regardless of the location. However, the correlated response of height based on diameter at breast height selection was similar to the direct gain for height, both at the same age and at different ages, showing that it is not necessary to obtain plant height, which is a trait that is more difficult to obtain data from and associated with higher errors.