Monika Sharma’s research while affiliated with University of Canterbury and other places

Resin defects can substantially decrease timber value in Pinus radiata, a commercial forest plantation species known for its good machinability. Tree breeding is a common approach to improve economic viability and product quality in commercial forestry. This study evaluated resin canal features in a P. radiata breeding population at two sites. Phenotypic resin canal features close to the pith differed significantly between the sites. The study estimated heritabilities for resin canal size, area, and density in 2-year-old trees as h² = 0.25, 0.42 and 0.23, respectively. The corresponding coefficients of genetic variations were 7.7%, 22.6% and 15.2%. Furthermore, resin canal features were assessed along radial cores of 6-year-old trees. Resin canal size increased with cambial age, while resin canal density and area showed minima 4 cm from the pith. Radial changes were accompanied with increased variation between families. While heritability and genetic variation would allow for selection at age 2-year-old, increased variation further from the pith could allow more accurate selections when trees are older. Genetic correlations between resin canal traits indicate that genotypes with larger resin canals tended to have fewer canals, larger trees having bigger but fewer resin canals and stiffer trees having less resin canal area.

Key message Radial grain patterns in young E. bosistoana trees are not random but are under genetic control and are correlated to other properties. Detailed high-resolution grain assessments match results from economical larger resolution techniques. Abstract Interlocked grain affects stem properties and timber value. Eucalyptus bosistoana is an emerging plantation species that is supported by a breeding programme, and which shows prominent interlocked grain. Grain assessments are difficult, either restricted in their spatial resolution or resource demanding. Comparative analysis of flexible and high-resolution X-ray microtomography grain measurements were shown to match the economical splitting test. Splitting demonstrated that, on average, grain in the 2-year-old E. bosistoana trees was straight close to the pith becoming slightly left-handed over the first 4 mm, but then developing a strong right-handed twist reaching an average of almost 5° by 12 mm. There was, however, a large degree of variability. Further, grain measures obtained from splitting tests correlated to the observed twisting of the stems. Lastly, twisting of timber was under genetic control. The combination of a heritability (h²) value of 0.34 and a coefficient of genetic variation value (rg) of 44% means that our assessment techniques for young trees could be incorporated into a breeding programme.

Trees in breeding programmes are often selected at 1/4–1/3 of rotation, called ‘early selection’, which is typically between 8 and 10 years in radiata pine. However, differences between populations and genotypes selected for either basic density or wood stiffness are already apparent at age 2. We report the application of very early screening techniques for wood properties in the New Zealand Radiata Pine Breeding Programme deployment populations. Approximately 3000 trees representing three populations with 92 families and 10 clones were grown in a common garden trial, leaning for 21 months to separate compression and opposite wood. The trees were harvested and analysis carried out separately by wood type. The trial showed the existence of large variability in wood properties at early age, in some cases similar to variability near rotation age, and moderate to high degree of genetic control ( $0.35 \le h^2 \le 0.71$ 0.35 ≤ h 2 ≤ 0.71 ). The genetic association between traits was strong, particularly between wood stiffness and longitudinal shrinkage ( $-\,0.69$ - 0.69 ) and between longitudinal and volumetric shrinkage (0.83), suggesting that improving stiffness would also have a strong effect on improving dimensional stability. Basic density was also associated with stiffness and shrinkage, but with lower predictive capacity. These results can be used for roguing deployment populations-which already contain superior growing trees-and quickly upgrade the wood quality of seeds and clones currently available to New Zealand forest growers. We discuss necessary modifications to turn this research work into operation to screen any new material before commercial release.

Main causes of drying degrade in most plantation-grown eucalypt timber are collapse and checking. Appropriate but costly sawing and drying techniques are employed to alleviate these problems. Eucalyptus globoidea is an emerging plantation species. This study investigated the genetic control of collapse and other tree features in an E. globoidea breeding population established at three different sites. Using a 14-mm diameter corer, thousands of E. globoidea trees representing 163 families were sampled, and genetic parameters for heartwood and sapwood collapse, extractive content, and heartwood diameter were estimated. Heartwood collapse was under genetic control with a narrow sense heritability ranging from 0.22 to 0.44. Considering the coefficient of genetic variability of ∼13–23%, heartwood collapse in E. globoidea can be reduced through selection. The significant genetic correlation between sites for heartwood collapse (rg = 0.73–0.83) suggested low genotype by environment (G × E) interaction. In line with the physical causes of collapse, heartwood collapse was positively correlated with extractive content. Extractive content and heartwood diameter are other traits of interest, as E. globoidea is grown for its ground-durable heartwood. The heritability of extractive content ranged from 0.40 to 0.71. Heartwood diameter was shown to be negatively correlated to extractive content. No significant genotype by environment (G × E) interaction was found for extractive content while genotype by environment (G × E) interactions for heartwood and sapwood diameter were small. Finally, 12 families had above-average heartwood diameter, extractive content, and below-average heartwood collapse. In summary, this study has shown that genetic selection for collapse and other wood properties of E. globoidea is feasible.

Trees in breeding programmes are often selected at 1/4-1/3 of rotation, called "early selection", which is typically between 8 and 10 years in radiata pine. However, differences between populations and genotypes selected for either basic density or wood stiffness are already apparent at age 2. We report the application of very early screening techniques for wood properties in the New Zealand Radiata Pine Breeding Programme deployment populations. Approximately 3,000 trees representing three populations with 92 families and 10 clones were grown in a common garden trial, leaning for 21 months to separate compression and opposite wood. The trees were harvested and analysis carried outseparately by wood type. The trial showed the existence of large variability in wood properties at early age, in some cases similar to variability near rotation age, and moderate to high degree of genetic control (0.35 <= h2 <= 0.71). The genetic association between traits was strong, particularly between wood stiffness and longitudinal shrinkage (-0.69) and between longitudinal and volumetric shrinkage (0.83), suggesting that improving stiffness would also have a strong effect on improving dimensional stability. Basic density was also associated to stiffness and shrinkage, but with lower predictive capacity. These results can be used for roguing deployment populations—which already contain superior growing trees—and quickly upgrade the wood quality of seeds and clones currently available to New Zealand forest growers. We discuss necessary modifications to turn this research work into operations to screen any new material before commercial release.