Epsilon Open Archive

Abstract

The objective of the studies this thesis is based upon was to increase knowledge of the genetics of traits related to wood volume, wood density and pulp yield in Eucalyptus urophylla and E. camaldulensis that could be used to enhance and accelerate tree improvement programs in Vietnam. Two provenance-progeny trials of E. urophylla in northern Vietnam testing 144 families, and three clonal trials of E. camaldulensis in southern, north-central and northern Vietnam testing a total of 172 clones were examined in these studies. In E. urophylla, significant between-provenance differences in growth traits were observed, but not in wood basic density or cellulose content. Estimated within-provenance heritabilities were 0.10-0.30 for growth traits, 0.60 for density and 0.50 for cellulose content. Estimated coefficients of additive genetic variation were 10% for growth traits, 6% for density and 4% for cellulose content. Selection efficiency for growth traits was found to be maximal at an age of 2-3 years, with an anticipated rotation period of 5-10 years. Genetic correlations between growth traits and density (0.10-0.28), growth traits and cellulose content (0.28-0.45), and cellulose content and density (-0.02) did not differ significantly from zero. Genetic correlations between the two sites in northern Vietnam, which were 60 km apart and had similar climate and soils, were high for both growth traits and wood density. In E. camaldulensis, clonal repeatabilities at ages 3 and 5 years were 0.18-0.42 for growth traits and 0.71-0.78 for density. The coefficient of genotypic variation was about 13% for growth traits and 6% for density. Genotypic correlations between growth traits and density (-0.16-0.24) did not differ significantly from zero. Between-site genotypic correlations were in the ranges of 0.32-0.56 for growth traits and 0.72-0.88 for density. Selection gains for diameter at breast height at each site at a selection proportion of 5% were 22-32%, with minor effects on density. Selection for diameter based on rankings of material at one site would yield gains in diameter at the other two sites that were only 40-60% of the gains obtainable from direct selection at those sites. Results from the studies suggest that considerable genetic improvement in eucalypt plantations grown for pulp production in Vietnam can be achieved through breeding and appropriate deployment. Strategies for management of genotype by environment interactions in breeding and clonal deployment of these species are discussed.