Dr. Harry Wu (CTIA Wood Quality Working Group Workshop)

Overcoming Adverse Genetic Correlations between Wood Quality and Quantity Traits in Advanced Breeding Generation of Radiata Pine

Radiata pine has been bred for three generations since the 1950s with realized genetic gain up to 33% for volume from the first generation and more than 10% predicted gain from the second generation in Australia. The focus of the third generation breeding in Australian national breeding program has shifted to wood quality traits with (1) development of economic breeding objectives, (2) integration of quantitative genetics, molecular genetics and wood science, and (3) application of Best Linear Unbiased Prediction (BLUP) and a Web-based interactive database for customized delivery of breeding values.  To further increase genetic gain, development of strategies dealing with adverse genetic correlation between wood volume and quality traits, infusion of new genetic material from the range-wide collections, increase of recombination rate and selection intensity, purging of inbreeding depression, deployment by clonal forestry will be critical.  In this paper, adverse genetic correlation between wood quality and quantity traits are summarized for radiata pine and optimal strategies to overcome such adverse genetic correlation are explored.

We surveyed 55 genetic studies published from 1960 to 2007 involving 11 growth-, form- and wood-quality traits in radiata pine.  Estimated heritability for wood-quality traits was higher than for growth and form traits. Among six wood quality traits, wood density had the highest heritability (0.63), followed by microfibril angle (0.61), spiral grain (0.55), fibre (tracheid) length (0.54), stiffness (0.50) and shrinkage (0.20).  It was found that growth rate (DBH) was adversely correlated with all wood-quality traits (for both density and mean stiffness r_g= -0.48). This indicates breeding for overcoming or at least coping with adverse genetic correlations is the most challenging issue in the advanced generation breeding for radiata pine.

We are developing two solutions to overcoming these adverse genetic correlations.  One short-term solution is to developing economic breeding objective for various end-products of radiata pine.  The economic breeding objective (economic weights) has been developed for the production of structural products and risk traits of radiata pine in Australia. A bio-economic model was constructed to linking radiata pine production system with breeding objective traits. The economic weights for breeding objective traits for structural products and risk traits were derived and used for development of selection index.  Optimal selection strategies in coping with adverse genetic correlation were studied using genetic parameters estimated in radiata pine and economic breeding objective. Results indicate that the optimal strategy is index selection using economic weights for breeding objective traits in radiata pine for short-term solution.  A long term solution is to dissecting the genetic base of the adverse correlations between wood quantity and quality traits and developing locus-based model to explore the best breeding strategies to overcome or breed out the adverse genetic correlations.

Key words:    Genetic correlation, wood quality, radiata pine, breeding objective, breeding strategy.