Comprehensive genetic dissection of wood properties in a widely-grown tropical tree: Eucalyptus

Background: Eucalyptus is an important genus in industrial plantations throughout the world and is grown for use as timber, pulp, paper and charcoal. Several breeding programmes have been launched worldwide to concomitantly improve growth performance and wood properties (WPs). In this study, an interspecific cross between Eucalyptus urophylla and E. grandis was used to identify major genomic regions (Quantitative Trait Loci, QTL) controlling the variability of WPs. Results: Linkage maps were generated for both parent species. A total of 117 QTLs were detected for a series of wood and end-use related traits, including chemical, technological, physical, mechanical and anatomical properties. The QTLs were mainly clustered into five linkage groups. In terms of distribution of QTL effects, our result agrees with the typical L-shape reported in most QTL studies, i.e. most WP QTLs had limited effects and only a few (13) had major effects (phenotypic variance explained > 15%). The co-locations of QTLs for different WPs as well as QTLs and candidate genes are discussed in terms of phenotypic correlations between traits, and of the function of the candidate genes. The major wood property QTL harbours a gene encoding a Cinnamoyl CoA reductase (CCR), a structural enzyme of the monolignol-specific biosynthesis pathway. Conclusions: Given the number of traits analysed, this study provides a comprehensive understanding of the genetic architecture of wood properties in this Eucalyptus full-sib pedigree. At the dawn of Eucalyptus genome sequence, it will provide a framework to identify the nature of genes underlying these important quantitative traits. (Résumé d'auteur

Corewood in South African pine: necessity and opportunities for improvement

South Africa has made excellent progress in breeding plantation trees fulfilling the primary demands of improved volume growth, stem and branching characteristics, tolerance to pests and diseases, and general adaptability. This has had marked positive impacts on wood quality, as straight stems normally contain no or very little reaction wood, while  problems associated with pith eccentricity and wandering pith are kept  to a minimum. The breeding of trees with small, well-distributed branches, forming large angles with the vertical axis of the tree stem, reduced performance problems associated with knots and knot-associated features. However, tree breeding and intensive silviculture are causing the average corewood diameter to increase, creating a wood resource that is increasing in variability, especially when combined with earlier harvesting. Reducing the size and improving the properties of the corewood zone have therefore become of utmost importance to ensure that the South African pine timber resource continues to meet quality demands related to strength, stiffness and stability. Breeding programmes to date have created sound bases for further wood quality improvement of the various pine species, especially of the corewood zone. Opportunities for success are excellent as large variation in corewood properties still exists within the current breeding populations, combined with operationally important wood properties, such as wood density, microfibril angle, spiral grain and transitional age, all being under moderate to strong genetic control. Corewood properties seem to be inherited largely independently of tree and growth characteristics, making it possible to combine improvement in these characteristics with desirable wood properties. This paper discusses results from several young field trials, which have shown marked family, species and site differences in wood stiffness. This suggests that there is good opportunity to increase the dynamic modulus of elasticity of corewood by early selection and breeding, using highly reliable non-destructive acoustic technology. The results also proved that vegetative propagation through cuttings has no detrimental effect on corewood stiffness. The latter may even increase with increasing physiological age of the cutting.Keywords: acoustics, corewood, juvenile wood, microfibril angle, modulus of elasticity, stiffness, wood densitySouthern Forests 2010, 72(2): 98–10

The wood properties and sawn-board quality of South African-grown Pinus maximinoi (HE Moore)

This report summarises results of past research in South Africa on the wood properties and qualities of P. maximinoi, supplemented by results of a study performed recently on an approximately 15.5-year-old provenance trial at Wilgeboom after it had been severely damaged by fire. The trees selected to study wood density, branching characteristics and sawn-board quality of the species, were previously selected for further breeding for their superior volume growth and stem form. Differences in mean internodal length and mean branch diameter were statistically highly significant among provenances, on average being longer and generally thicker than those of the P. elliottii and P. patula. The bark-layer of P. maximinoi was thicker than that of P. patula but it differed little in thickness with that of P. elliottii. Provenance means in air-dry wood density varied within a relatively narrow band of 0.457 to 0.483 g/cm3, with an average mature wood density resembling closely that of P. patula. However, P. maximimoi was characterised by increased uniformity in density across its radius, as it tended to form denser wood in the central parts of its stem, causing its pith-to-bark density gradient to be flatter. Growth rate had no effect on wood density, but improved radial density uniformity was clearly associated with increased growth rate. Sawn boards were of good quality and showed little warp after drying despite the fact that some of the trees were slightly crooked, with possibly a higher incidence of compression wood. Compared to P. patula and P. elliottii this species exhibited a darker brown colour with almost a reddish tinge when freshly cut. The annual rings were hardly recognisable on rough-sawn surfaces. Wandering pith often occurred in some boards as a result of the higher degree of stem crookedness. Since the branches of P. maximinoi tend to be arranged in whorls, it can be expected that the impact of knots on the strength of the sawn boards would predominantly be the result of the combined effect of knots grouped together, rather than individual knots. This is also a valuable attribute, as the species lends itself to the production of relatively long knot-free board sections from the unpruned parts of the stem, which would enable manufacturers of finger-jointed products to increase the volumes and diversity of their products, especially where appearance is important. Loose knots occurred more frequently in boards cut from P. maximinoi compared to the two controls, most likely as a result of pruning that was carried out too late considering the fast growth of the species. Keywords: Pinus maximinoi, provenances, wood density, knots, CAMCORE, sawn-board quality Southern African Forestry Journal Vol. 208, 2006: 39-4

The wood quality of Pinus chiapensis (Mart.) Andresen grown in the Mpumalanga forest region: scientific paper

The ten best performing families selected in a Pinus chiapensis trial at Tweefontein forest near Sabie have been evaluated for wood and saw timber properties. The wood was found to be soft, remarkably uniform both within and between annual rings, stable, with a well-defined heartwood zone. The latewood proportion of the annual rings was extremely small, resulting in a poorly defined ring structure. The fifty trees studied had an average air-dry density of 0,420 g / cm3 (extracted and at 12 % moisture content) with individual tree densities varying from 0,380 to 0,465 g / cm3 at 0,8 m height level. Differences between families were highly significant, suggesting that there is a strong potential to increase the density of the wood through tree breeding. Knots were relatively small and well shaped, and normally occurred in small clusters. Knot occlusions following pruning were accompanied by little grain distortion. When present, the amounts of included resin, pieces of bark and other debris at the occluded pruning cuts, were small and of little practical significance. The wood machined without any difficulty in the wet and dry condition. Boards dried without any significant drying degrade, but moisture loss during drying from the heartwood zone was markedly slower compared to what is normally experienced with the pith zone of other South African commercial pines. Some sawn pieces may not be suitable for some structural purposes where strength is important, while tests on Colombian and Brazilian grown P. chiapensis have shown that the species may not be acceptable for pulp production because of low pulp yields and high alkali consumption. Owing to its high degree of uniformity it might be well suited for special products such as for internal construction purposes, panelling and other decorative work, woodcarving and some applications in the furniture manufacturing industry. It might also be suitable for the manufacturing of items such as match sticks, toothpicks, clothes-pegs and other small wooden objects. Southern African Forestry Journal No.192 2001: 51-5

Some notes on the effect of wet-storage on timber: review paper

The storage of logs under water sprays has proved to be a highly effective method to preserve logs over prolonged periods against drying defects and infestation by staining fungi. Wet-storage has little effect on wood quality apart from some degradation of the thin outer layer of the log, as well as an increase in moisture content. Strength loss seems to be rare and when it occurs it develops slowly. The only changes to the wood of practical significance are caused by the activity of anaerobic bacteria during the storage period. The porosity of the wood tends to increase while the colour of the wood might change towards a darker tinge. While a slight colour change might be problematic in some avenues of utilisation, the increased porosity could either be a friend or a foe. The increased porosity allows chemicals and moisture to diffuse quicker through the wood, making drying and preservative treatment somewhat faster and easier. However, difficulties have been reported which probably relate to differences in porosity caused by differences in bacterial activity within the log during wet-storage. These include differences in drying rates, causing differences in moisture content between and within boards at the end of a drying cycle, and uneven absorbance of surface finishing layers in pine furniture manufacture. P. taeda saw logs containing large amounts of abnormal compression wood, which were kept in wetstorage for prolonged periods, yielded boards that were considerably less prone to distortion during processing. The wet-storage of eucalypt logs has proved to be a useful method of reducing growth stressrelated defects such as log splitting and board distortion. Wet-storage was also found to be an effective means of rendering susceptible timber more immune to powder-post beetle (Lyctus) attack. In general it appears that the advantages of wet-storage outweigh the problems associated with it which, in any case, can be dealt with relatively easily in practice. Key Words: Log storage; Wet-storage; Water spray storage; Wood quality; Wood preservation; Wood processing; Bacterial activity Southern African Forestry Journal Issue 202 2004: 77-8

The quality and wood properties of 4 provenances of South-African-grown Pinus tecunumanii

The wood properties of 4 provenances of South-African-grown Pinus tecunumanii (ie Yucul, Camelias, Mountain Pine Ridge and St Rafael) were examined and compared with those of 3 commercial controls, ie Pinus patula, Pinus elliottii and Pinus taeda. Trials planted at 2 sites were evaluated. The rate of growth and stem form of the 4 P tecunumanii provenances were found to be very similar to that of the 3 controls used in the study, but crown breaks were very common, probably due to the tendency of P tecunumanii to develop heavy branch whorls. Tracheid lengths and the pattern of within-tree variation were found largely similar among the various groups of trees studied, but in comparison with the controls, the tracheid cells of P tecunumanii were markedly larger in cross-sectional diameter because of their thicker walls and larger lumen diameters. However, differences in the proportion of cell-wall material among the groups of trees studied were small. At both sites the annual ring structure of the wood of P tecunumanii differed pronouncedly from that of the controls, having a mean latewood percentage of only about half of that of P patula and about one-third of that of P taeda and P elliottii. In spite of the large relative proportion of earlywood characterising the wood of P tecunumanii, it produces wood very similar in density to that of P patula and P taeda and slightly higher than that of P elliottii. This was found due mainly to the fact that the broad earlywood zones of the Pinus tecunumanii provenances were substantially more dense than those of the commercial controls while differences in latewood densities among the various groups considered were small and non-significant. Apart from the relatively low intra-ring varability characterising the wood of P tecunumanii, all provenances of this species were found to be less variable in density in both the radial and axial directions in the stem, compared to the control species. The higher degree of uniformity of the wood produced by this species makes it a very promising alternative to some other South-African-grown pines, especially on productive, frost-free sites.Les qualités et propriétés du bois de 4 provenances de Pinus tecunumanii d'Afrique du Sud. Les propriétés du bois de 4 provenances de Pinus tecunumanii d'Afrique du Sud (ie Yucul, Camelias, Mountain Pine Ridge et Saint-Rafael) ont été examinées et comparées à celles de 3 standards commerciaux, ie Pinus patula, Pinus elliottii et Pinus taeda. Des échantillons prélevés sur 2 sites ont été étudiés. Les résultats sont présentés dans le tableau I. Le taux de croissance et la forme du tronc de 4 provenances de P tecunumanii se sont révélés très similaires à ceux des 3 standards commerciaux (tableau I) mais les cassures de couronnes étaient très fréquentes, probablement à cause de la tendance du P tecunumanii à développer de grosses branches. Les longueurs des trachéides et la forme des variations intra-arbres se sont révélées largement similaires pour les divers groupes d'arbres étudiés mais, par rapport aux standards commerciaux, les trachéides des P tecunumanii sont notablement plus larges en diamètre trans-section du fait de leur paroi plus large et du diamètre luminien plus important (figs 5 et 6). Cependant, les différences de proportions de leur paroi cellulaire entre les groupes d'arbres étudiés sont apparues faibles (fig 7). Sur les 2 sites, la structure du cerne annuel du bois de P tecunumanii diffère sensiblement de celle des espèces témoins ; le cerne du bois de P tecunumanii présente une proportion de bois final qui équivaut seulement à la moitié de celle du P patula et à peu près à 1 tiers de celle du P taeda et du P elliottii (fig 2). En dépit de la proportion de bois initial relativement importante qui caractérise le bois de P tecunumanii, la densité du bois est très similaire à celle du P patula et du P taeda, et sensiblement plus élevées que celle du P elliotti (fig 3). Cela est dû prinicipalement au fait que les zones de bois initial des provenances de P tecunumanii sont notablement plus denses que celles des espèces témoins alors que les différences pour la densité du bois final entre les différents groupes considérés sont faibles et non significatives (fig 4). En dehors de la variation intra-cerne relativement faible qui caractérise le bois de P tecunumanii, toutes les provenances de cette espèce se sont révélées peu différentes en densité dans les directions radiale et axiale du tronc en comparaison des espèces témoins. Le degré d'uniformité plus élevé pour le bois produit par cette espèce en fait une alternative très prometteuse par rapport aux autres pins sud-africains, spécialement sur les sites productifs et à l'abri des dégâts de gelée

Clonal differences in log end splitting in Eucalyptus grandis in relation to age, parent performance, growth rate and wood density in two even-aged trials in Mpumalanga, South Africa

This paper discusses the juvenile–mature correlation of log end splitting among Eucalyptus grandis clones from two trials and how differences in splitting relate to differences in wood density, pith-to-bark gradient and growth rate. Two approximately 20-year-old Eucalyptus grandis clonal trials at Bergvliet plantation were sampled. The first trial (Trial A) consisted of clones of eight ortets (genotypes) specifically selected for their widely different propensities to develop end splitting. The second trial (Trial B) consisted of 80 clones and one seedling control. From the latter trial 15 clones were selected in such a manner that they constituted three groups of clones representing a combination of high- and low-volume producers and, among the high-volume producers, clones exhibiting high and low propensities towards end splitting. The fourth group represented the seedling control. Trial A showed highly significant clonal differences in splitting, basic wood density, as well as its pith-to-bark gradient. No relationship of splitting with differences in growth rate, density or density gradient was found. The clones derived from the low- and high-splitting ortets maintained their general statuses as low and high splitters over a considerable period of time, but some of the individual clones did not reflect the performance of the ortets from which they were derived. Trial B revealed that clones classified as good-volume producers at the age of 65 months still outperformed the clones classified as low-volume producers approximately 15 years later. No significant differences in average wood density between the groups of clones studied was found, irrespective of differences in growth rate and degree of splitting, but trees from the slow-growing group of clones were significantly more variable across the radius in average wood density. The outcome of both trials confirmed results of many previous studies on this species, in that rapid and uniform growth has no significant detrimental effect on wood density or its rate of change across the radius of the tree. It may, in fact, be associated with increased uniformity from pith to bark with increasing age, sometimes resulting in slightly increased overall wood density. Keywords: Eucalyptus grandis, growth stresses, juvenile–mature correlation, splitting, wood densitySouthern Forests 2008, 70(1): 37–4

The effect of planting density on the wood quality of South African-grown Eucalyptus grandis

This paper presents the results of a wood property and sawn board quality study performed on disc samples and sawlogs taken from a 23-year-old Eucalyptus grandis Nelder 1a spacing trial at J.D.M. Keet plantation near Tzaneen. Ten trees from each of four markedly different planting densities were chosen to provide contrasting material to study the effects of growth rate on the quality of the wood produced. Spacing treatment diameter means ranged from 18.9 to 57.9 cm. An inverse relationship was found between planting density and wood density. Typical pith-to-bark density profiles for trees at this age occurred in the trees with rapid growth, i.e. steep gradients from the pith towards the bark during the early stages of growth, followed by a gradual transition into more constant mature wood density values. Trees of which the growth had been curbed by higher planting densities, on the other hand, showed little sign of levelling off. As a result, the faster growing trees contained significantly larger proportions of relatively homogeneous wood compared to the slower grown trees, giving them an obvious quality advantage over slower grown trees. Accelerated growth thus seems to yield trees that can be utilized more effectively and converted into products with more reliable performance characteristics. Fast growth seemed to promote interlocking grain, but the correlation with interlocking grain severity was too poor to be of any practical significance. Mean splitting showed a downward trend with decreasing planting density, but statistically the differences were non-significant. A statistically significant correlation was found between the amount of splitting in logs and the proportional length of sawn boards affected by splits immediately after wet-mill processing. At the end of the sawmilling process, however, such correlation did not exist any longer, suggesting that the boards responded differently to drying stresses and impacts during handling and transport with regard to further splitting. No significant effect of planting density on sawn volume losses due to splitting or collapse could be detected. Keywords: silviculture, planting density, growth stress splitting, wood density, collapse, saw-timberSouthern African Forestry Journal No. 205 2005: 31-3