Dane Thomas

Pectin Methylesterase Genes Influence Solid Wood Properties of Eucalyptus pilularis

This association study of Eucalyptus pilularis populations provides empirical evidence for the role of Pectin Methylesterase (PME) in influencing solid wood characteristics of Eucalyptus. PME6 was primarily associated with the shrinkage and collapse of drying timber, which are phenotypic traits consistent with the role of pectin as a hydrophilic polysaccharide. PME7 was primarily associated with cellulose and pulp yield traits and had an inverse correlation with lignin content. Selection of specific alleles in these genes may be important for improving trees as sources of high-quality wood products. A heterozygote advantage was postulated for the PME7 loci and, in combination with haplotype blocks, may explain the absence of a homozygous class at all single-nucleotide polymorphisms investigated in this gene.

Genetic association studies in Eucalyptus pilularis Smith (blackbutt)

Summary Breeding for wood quality is limited by the long generation times and the delay before wood quality can be measured reliably. Association studies allow links between phenotype and genotype to be made, and are a prelude to accelerated domestication of trees by molecular breeding approaches. This study uses association genetics to identify DNA polymorphisms that correlate with solid wood properties of Eucalyptus pilularis Smith (blackbutt). We undertook extensive phenotyping of dimensional stability, growth and structural wood properties on a nine-year-old progeny trial established by Forests NSW at Hannam Vale, near Port Macquarie in NSW. A subset of 372 phenotyped individuals representing 284 families collected from 37 provenances was used as the association population for genotypic assessment. Fifty-two out of 127 novel DNA polymorphisms were surveyed within four candidate genes, CCR, CAD, MYB1 and MYB2. Several putative associations between wood quality traits and selected DNA polymorphisms are reported, along with the likely mechanism of action on wood quality. Association studies such as this will facilitate non-destructive DNA tests for heritable wood properties that can be used to enrich breeding populations at any developmental stage with desirable alleles.

Review of growth and wood quality of plantation-grown Eucalyptus dunnii Maiden

Summary Forests NSW manages Eucalyptus plantations on the north coast of NSW, Australia, for high-value timber production. One species increasingly being planted both in Australia and overseas is Eucalyptus dunnii Maiden. For a species to be considered suitable for forestry, criteria to be met include successful establishment, growth and suitability for end use, be that pulp, solid wood or veneer production. Historic data from E. dunnii plantations aged from 3 to 34 y were reviewed. Growth and wood quality using a range of non-destructive and destructive measurements are reported. Eucalyptus dunnii typically grew equally well as some alternative species, although species ranking was affected by the growing site. Eucalyptus dunnii produced high-quality wood chips with average pulp yield from three NSW plantations aged 8–10 y of 53% and 265 kg m−3. This yield is comparable with that of 10-y-old E. globulus plantation material from Tasmania. Wood density increased with tree age from about 500 kg m−3 at age 10 y to 600 kg m−3 at age 25 y, and more slowly beyond that age. Many solid-wood quality traits such as hardness and strength could be positively correlated with both tree age and basic density. This has implications for the timber industry as it is intended that plantation trees will be harvested at younger ages than native forest trees, but wood quality in such younger material may not satisfy minimum product performance requirements. However, trees selected for higher density achieved strength group ratings at age 9 y that would normally be achieved at age 25–30 y. It is not known if similar improvements can be made in other wood quality traits. Quality traits requiring further examination are growth stresses and end splitting of logs, and shrinkage of sawn timber. Collapse (reversible shrinkage) and non-reversible shrinkage are positively related to wood density, but a greater concern is the high ratio of tangential shrinkage compared to radial shrinkage. This ratio, which can be 2.5 or greater in E. dunnii, leads to excessive distortion in sawn material. It may be possible to reduce overall wood shrinkage and the ratio of tangential to radial shrinkage, as well as other unfavourable wood quality traits, through genetic selection as these traits in related eucalypts (e.g. blackbutt, E. pilularis) are heritable.

Crown structure and vertical foliage distribution in 4-year-old plantation-grown Eucalyptus pilularis and Eucalyptus cloeziana

Tree growth and form are both influenced by crown architecture and how it effects leaf distribution and light interception. This study examined the vertical distribution of foliage in 4-year-old plantation-grown Eucalyptus pilularis Sm. and E. cloeziana F. Muell. trees. Leaf area (LA) distribution was determined at two different sites using allometric approaches to determine LA in crown sections and for whole trees. Leaf area was distributed more towards the upper crowns when canopies had been closed for longer. Leaf area was also skewed more towards the upper crowns for Eucalyptus pilularis than E. cloeziana. These species differences were consistent with differences in vertical light availability gradients as determined by point quantum sensors. Leaf area of individual branches was highly correlated with branch cross-sectional area (CSA) and whole-tree LA was closely related to stem CSA. Branch-level allometric relationships were influenced by site and crown position. However, the general allometric equations between stem size and whole-tree leaf area could be applied across sites. Results from this study suggest that pruning of live branches in these species should follow species-specific guides for the timing and height of pruning to optimise the effects on stem growth and form.

Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments

This study investigates the putative role of thicker leaves in enhancing photosynthetic capacity and water-use efficiency (WUE) of Eucalyptus species native to xeric environments. Three Eucalyptus species, Eucalyptus grandis Hill. (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis (Endl.), were grown under well-watered or water-limited conditions in a single compartment of a temperature-controlled glasshouse. Eucalyptus grandis is native to a mesic environment while E. sideroxylon and E. occidentalis are native to xeric environments. Leaves of E. sideroxylon and E. occidentalis were thicker and contained more nitrogen (N) on a leaf-area basis than E. grandis. Leaf gas-exchange measurements indicated that the photosynthetic capacity of E. sideroxylon and E.occidentalis was greater than E. grandis and that stomatal conductance and WUE were negatively correlated. Whole-plant, gas-exchange and carbon-isotope measurements showed that E. sideroxylon and E. occidentalis had lower WUE than E. grandis under both well-watered and water-limited conditions. However, there was no difference in N-use efficiency between species. We suggest that stomatal conductance and leaf N content are functionally linked in these seedlings and conclude that thick leaves can, in some conditions, result in low WUE.

Predicting pulp yield and pulp productivity of Eucalyptus dunnii using acoustic techniques

Summary The economics of kraft pulping are influenced by variation in wood density and chemistry, or their product, pulp productivity. The ability to predict basic density, pulp yield or pulp productivity before harvest would provide an economic advantage to the grower or processor. Acoustic velocity in green wood is correlated with both basic density and pulp yield, offering potential for rapid screening. We explored relationships between acoustic velocity, density, pulp yield and fibre length using data from Eucalyptus dunnii plantations in northern NSW, Australia. Acoustic velocity measured on logs accounted for 27% of the variation in pulp yield and 50% of variation in pulp productivity. The strong relationship between fibre length and pulp yield is proposed as a possible causal mechanism. A threshold acoustic velocity of 3.65 km s−1 was defined as the point at which logs would produce at least 250 kg of dry pulp per cubic metre of green wood. Removal of the worst 25% of logs, based on velocity, would give a 2.2% gain in pulp productivity which equates, in turn, to an additional 6.2 kg of pulp produced from every cubic metre of green wood.

Variation in growth and Quambalaria tolerance of clones of Corymbia citriodora subsp. variegata planted on four contrasting sites in north-eastern NSW

Summary Genetic parameters, including heritabilities, trait-trait correlations and across-site correlations for growth traits and quambalaria shoot blight damage were estimated in four Corymbia citriodora subsp. variegata clonal trials in northern New South Wales, Australia. Additive and non-additive variances were calculated separately to allow the estimation of broad—and narrow-sense heritabilities. Quambalaria shoot blight damage at ages 1 and 3.5 y was under predominantly non-additive genetic control (H2 = 0.02–0.46, h2 = 0–0.17). Growth traits at age 5 y were under moderate genetic control (H2 = 0.32–0.54, h2 = 0–0.54). Growth traits were strongly correlated with quambalaria shoot blight damage. Across-site correlations were low for quambalaria shoot blight damage (rg = 0.13–1.00) but high (>0.8) for the growth traits. Index selection was used to determine the most efficient selection strategies for improvement of growth and disease tolerance.

SNP discovery and association mapping in Eucalyptus pilularis (blackbutt)

Background This research explores the universality of genetic variation in genes controlling wood formation across the genus Eucalyptus. Breeding and deploying Eucalypts for improved wood quality is constrained by the delay before wood traits can be measured reliably. Marker assisted selection (MAS) offers aw ay to make earlier selection of wood properties, by selecting Single Nucleotide Polymorphisms (SNPs) in the DNA which can predict specific phenotypic traits (genotype-phenotype links). SNPs shared between species (trans-specific SNPs) may have broad application to multiple species. When the species are more distantly related, ancient SNPs shared between subgenera (trans-subgeneric SNPs) are likely to be of adaptive importance and persist in separate lineages due to balancing selection [1]. Sample and methods

Corrigendum to: Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments

This study investigates the putative role of thicker leaves in enhancing photosynthetic capacity and water-use efficiency (WUE) of Eucalyptus species native to xeric environments. Three Eucalyptus species, Eucalyptus grandis Hill. (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis (Endl.), were grown under well-watered or water-limited conditions in a single compartment of a temperature-controlled glasshouse. Eucalyptus grandis is native to a mesic environment while E. sideroxylon and E. occidentalis are native to xeric environments. Leaves of E. sideroxylon and E. occidentalis were thicker and contained more nitrogen (N) on a leaf-area basis than E. grandis. Leaf gas-exchange measurements indicated that the photosynthetic capacity of E. sideroxylon and E.occidentalis was greater than E. grandis and that stomatal conductance and WUE were negatively correlated. Whole-plant, gas-exchange and carbon-isotope measurements showed that E. sideroxylon and E. occidentalis had lower WUE than E. grandis under both well-watered and water-limited conditions. However, there was no difference in N-use efficiency between species. We suggest that stomatal conductance and leaf N content are functionally linked in these seedlings and conclude that thick leaves can, in some conditions, result in low WUE.