Genetic improvement of the wood properties of Eucalyptus nitens : breeding to improve solid wood and pulp properties

Eucalyptus nitens is a hardwood plantation species used in cool-temperate regions of the world. It is mainly used for pulp and paper, although there is increasing interest in using this species for producing high quality appearance and structural timber products. Therefore breeding programs need to consider the requirements of different markets and breed for a variety of end-uses. The aim of this thesis is to study the genetic control of E. nitens wood properties. The focus is on three different product groupings which are pulp and paper, appearance grade timber, and structural grade timber. Pulp and paper traits studied were wood density, cellulose content, fibre length and fibre coarseness; appearance grade timber traits were collapse, checking and decay; and structural grade timber traits were stiffness and microfibril angle. Genetic parameters and potential genetic gains were estimated using data from 12 year old E. nitens progeny trials grown on three sites. Wood properties were sampled using 12 mm cores taken at a height of approximately 1 metre. Relationships between whole tree wood density and core wood density, and whole tree pulp yield and core cellulose content were investigated. For both traits core samples were good predictors of whole tree values. Methods were developed to assess wood collapse and decay using wood cores. All wood properties except fibre coarseness had significant genetic variation, with heritabilities ranging from 0.38 to 0.56. The heritability for stem diameter was 0.39. Genetic correlations between traits were mostly significant and reasonably high. Adverse correlations occurred between diameter and density, diameter and collapse, diameter and stiffness, and between density and cellulose. Favourable correlations occurred between diameter and cellulose, density and collapse and between density and stiffness. Genotype by environment interactions were sometimes present but were always small. Genetic selection can significantly improve the quality of wood produced for pulp and paper, appearance grade timber and structural grade timber. Of particular importance are the potential gains in collapse (or checking) and stiffness, where genetic selection can potentially lift the quality grades of appearance and structural products. Selecting a deployment population for high decay resistance may minimise the risk of value loss on sites known to have severe decay problems. Breeding goals for all product groupings are reasonably well correlated and improved product quality can be achieved in all product groupings without the need for specialised breeds. Selecting for wood density, as well as growth rate, is a minimum requirement if high grades of timber are to be produced