Genetic variation and genetic gain in growth traits, stem-branch characteristics and wood properties and their relationships to Eucalyptus urophylla clones

Growth traits, wood properties, stem-branch characteristics and bark percentage were assessed for 60 Eucalyptus urophylla S.T. Blake clones in southern China measured at age 21, 52, 71 and 96 months. Analysis of variance showed that there were significant differences on growth traits, wood properties and individual tree wood weight among clones. Coefficients of genotypic variation ranged from 12.12% to 53.16% for growth traits, 9.02% to 20.18% for wood properties, 21.75% to 22.71% for stem-branch characteristics, 28.31% for bark percentage and 51.20% for individual tree wood weight. Repeatability ranged from 0.36 to 0.53 for growth traits, 0.35 to 0.51 for wood properties, 0.21 to 0.24 for stembranch characteristics, 0.07 for bark percentage and 0.31 for individual tree wood weight. The strongly negative genotypic correlations suggesting that selection on growth traits at 21 months can not be effective to predict growth traits at 96 months whereas it could be used to predict growth traits at 52 and 71 months. The genotypic correlations between growth traits and basic density were ranged from -0.78 to 0.28 and weakly positive phenotypic correlations were found between growth traits and basic density, ranging from 0.03 to 0.09. The selection gain on diameter at breast height over bark by different selection proportions at 21, 52, 71 and 96 months old expressed that selection gain at 71 months was some what higher than that at other ages during 10% to 30% selection proportion, while selection gain at 52 months was some what higher than that at other ages during 60% to 90% selection proportion. Wood properties and individual tree wood weight which are strongly related to end production and economically important in pulp production should be studied extensively especially for pulp breeding.