Selection for solid wood properties in Eucalyptus nitens
By Mari Suontama, Toby Stovold, Russell McKinley, Mark Miller, Kane Fleet, Charlie Low, Heidi Dungey, June 2016.
Download SWP-T005 (pdf)
Eucalyptus nitens can be recognised as one of the tree species in New Zealand with an advanced breeding programme that is moving towards its fourth generation. Eucalyptus nitens is one of the most important commercially planted eucalypt species in the world, being the second most widely planted eucalypt in its native country Australia (Hamilton et al. 2008). In Australia, it is mainly grown for pulp wood but also for solid wood production (Hamilton et al. 2008). The majority of the production market for E. nitens is as pulp wood, hence breeding objectives and selection in this species is usually based on growth, wood density and form. In spite of the fact that environmental effects such as site characteristics and silvicultural regimes have influence on commercially important traits, we have a strong indication that these traits can be considerably improved by breeding.
New breeding objectives for solid wood production were proposed in the current breeding plan and regarded as an essential focus for selections in the next generation (Stovold et al. 2010). This initiated the current project with its objective to measure a progeny trial for wood properties at theestate of the New Zealand’s largest E. nitens producer South Wood Export Ltd (SWEL). This project began as a part of the Diversified Species Programme in 2014-15, and was subsequently included in the Specialty Wood Products Research Programme Partnership in 2015-16.
The Keens Block progeny trial used for this wood quality study. The trial was assessed for growth, form, and wood density with a total number of 3600 trees at age six in 2013 (Baltunis et al. 2013). This third generation progeny trial comprising of 115 elite mother trees from the second generation. Phenotypic data for wood properties including wood density, growth strain, stiffness, shrinkage/collapse and internal checking was collected on 752 trees at age seven during 2014- 2015. Quantitative genetic analysis was carried out to recommend an optimised seed-orchards establishment plan to SWEL.
All traits used in the selection for solid wood production showed moderate estimated heritabilities. This implies that breeding will result in improved tree material for sawn timber properties in this population. Genetic correlations between traits were mainly favourable but some of them only indicative and therefore inconclusive. Predicted genetic gains were considerable for the traits when selecting the top 5% of individuals in the population. The highest genetic gains were predicted for internal checking in sapwood and heartwood (30%, 51%). Air-dry and reconditioned shrinkage measurements on averaged 3-6m logs also showed good genetic gains (6 to 10%). Improvement in growth stress was estimated at 8% based on predicted gains. These estimated genetic gains did not take into account genetic correlations between the traits and therefore may differ when selecting simultaneously for all traits of interest. Indication of mainly favourable and not highly adverse genetic correlations is assuring in terms of the potential to achieve desired gains for the aggregate breeding objective. However, due to the indicative nature of genetic correlations, to maximise the progress for each production purpose, separate breeding objectives for solid wood and pulp wood production are recommended.
More information will be received through genomic prediction implemented into this population. Multiple trait analysis using genomic selection would further increase our knowledge of genetic correlations between traits and will finalise the decision of traits that should be included as selection criteria in future breeding plans for E. nitens.
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