Genetics, breeding and deployment of Melaleuca and Norway spruce

Additive effects of genes are cumulative over generations and are the main source of genetic variation exploited by most plant breeding programs. However, the relative importance of additive and non-additive genetic effects is critical information required to properly evaluate the potential for genetic gain from various breeding programs and deployment options used in the genetic improvement of forest trees. Melaleuca cajuputi is a moderately fast-growing tree species considered as a multipurpose species in Australia and South-East Asia. Breeding programs of M. cajuputi have been conducted for three decades. In Vietnam, genetic improvement of subsp. cumingiana aims to enhance tree growth for wood production. Genetic analysis of growth, stem form, modulus of elasticity (MOE), bark thickness and bark ratio was examined from 80 half-sib family progeny trial. Narrow-sense heritability ranged from zero to 0.27. MOE had positive genetic correlations with growth. Selection based on volume and MOE showed genetic gains of 31% in volume and 6% in MOE. The optimal early selection age for growth based on DBH alone was four years. A second breeding objective for M. cajuputi subsp. cajuputi aims to improve oil yield and 1,8-cineole content. Data collected from single trial including 39 full-sib families from 12 parents was analyzed. Narrow-sense heritability were 0.10–0.13 for growth, 0.50 for oil yield and 0.21 for 1,8-cineole content. Genetic relationships among growth, oil concentration and 1,8-cineole content were almost independent. The most optimal selection scenario improved 2.18% in 1,8-cineole content and 27.36% in leaf oil yield. Genetic improvement of Norway spruce (Picea abies) has been carried out for over six decades in Sweden. A large clonal testing program was launched during the mid- 1970s. This study evaluated genetic variations for growth and wood quality traits (i.e. Resi, Pilo, AV, MOE and GA) from the six full-sib and two half-sib clonal trials in order to study benefits and risk of implementing clonal forestry. Additive genetic variation accounted for majority of the total genetic variation associated with DBH and wood traits whereas non-additive genetic variation appeared to be more important for height at early ages. Predicted genetic gain was the highest for clonal deployment, followed by full-sib family deployment and open-pollinated deployment. Consequently, clonal forestry could lift genetic gain about 11–31% more for wood traits and 22–120% more for DBH over full-sib family forestry. About 30–40 clones for each family could obtain the maximum clonal genetic gain in clonal testing and selection.