Brian Butterfield

Characterization of mechanically perturbed young stems: can it be used for wood quality screening?

Abstract• IntroductionGenetic testing is the slowest part of a breeding cycle. There is a growing interest in early wood quality screening methodologies. We hypothesized that subjecting 8-month-old radiata pine trees to mechanical perturbance induces reaction wood that permits isolating their likely corewood features.• MethodsFour clones were grown straight, tied at 45° from the vertical, or rocked on a purpose-built frame. Trees were assessed for growth, basic density, compression wood, number of resin canals, and three acoustic stiffness (MoE) measures with an ultrasonic timer.• ResultsThere were no significant differences between stem postures for growth. Both rocked and straight trees developed similar levels of compression wood (between 13% and 17%). Rocked trees had a significantly larger number of resin canals than straight trees. Rocked trees produced the lowest MoE for all acoustic assessments. Clonal rankings for MoE were consistent between standing tree and green stemwood MoE. There were small ranking differences for dry stemwood MoE. Clone F, which expresses low MoE as an adult tree, had consistently the lowest MoE assessments but also the highest basic density.• ConclusionThe observed differences in wood properties between clones make feasible their use for screening purposes at an early age.

The Distribution of un-esterified and Methyl-Esterified Pectic Polysaccharides in Pinus Radiata

A cationic dye which binds acidic polymers such as pectin and monoclonal antibodies, directed against un-esterified and methyl-esterified (JIM5) and only methyl-esterified (JIM7) pectin epitopes, were used, in conjunction with light microscopy, confocal microscopy and immunogold electron microscopy, to study the spatial distribution of pectin in the xylem tissue of Pinus radiata D. Don. Histochemistry demonstrated that pectin was located in the compound middle lamella (CML) of the maturing tracheid cell wall, in addition to the pit membranes and the CML of the ray cell walls. Immunogold labeling showed differential distribution of the pectin epitopes within the CML of the maturing cell walls. Moreover, in the xylem, the JIM5 and JIM7 epitopes were found to be restricted to distinct tissues. Neither epitope occurred in the secondary walls of the xylem cells. These patterns of epitope expression were not maintained in the mature cell. These results represent the first demonstration of restricted spatial patterns of distribution of these epitopes in the xylem tissue of radiata pine and are consistent with results from other coniferous gymnosperms.

Intra-ring checking in Pinus radiata D. Don: the occurrence of cell wall fracture, cell collapse, and lignin distribution

Ultrastructural and cytochemical features of tracheid cell walls were examined in oven-dried Pinus radiata D. Don disks that demonstrated a range in severity of the wood quality flaw referred to as “intra-ring checking,” from severe to none. Observations of the tracheid cell wall at the ultrastructural level included the localization of the origin of tears between adjacent cells, and the occurrence of tracheid collapse. Cytochemical analysis focused on determination of the spatial distribution of lignin within the cell wall layers. Tracheid lignin content was further quantified using the Klason and acetyl bromide methods. We found considerable homogeneity in the point of failure in the wood demonstrating intra-ring checking, with 80% of the tears occurring at the compound middle lamella (CML)/S1 cell wall interface. In these samples, tracheid collapse was observed adjacent to the tear as well as between tears, and the cell walls appeared to have altered lignin distribution, particularly in the S1 wall layer. We suggest that alterations in the CML/S1 layers create a weak point in the cell wall, making it prone to the observed tears. The mechanisms that may be involved in the occurrence of intra-ring checking are discussed at the morphological level.

Are Rays and Resin Canals Causal Sites for Intra-Ring Checking in the Wood of Pinus Radiata?

Pinus radiata D. Don (radiata pine) wood can develop a wood quality defect called ‘intra-ring checking’ (checks) during kiln drying. A study was conducted to examine if rays and resin canals were the initiation sites of checks, and if the presence of the rays and resin canals increased the susceptibility of radiata pine wood to checking. The structural features associated with checking were observed in images of thirteen oven-dried radiata pine disks. Six of the sixty checks observed were associated with rays and resin canals. It is clear from the observations that rays and resin canals could not be the primary sites for check development. A comparative study showed some differences between the checked and non-checked wood with respect to rays and resin canals. Checked wood showed a higher amount of tissue area occupied by rays than the nonchecked wood. Hence, it is possible that rays can influence the tendency of wood to check. Such a relationship was not seen with respect to resin canals. However, a difference in the arrangement of resin canals was observed between checked and non-checked wood. Checked wood showed a scattered arrangement of resin canals, while the non-checked wood showed a linear arrangement.

Compression Wood does not Form in the Roots of Pinus Radiata

We investigated the potential for the roots of Pinus radiata D. Don to form compression wood. Compression wood was not observed in either the tap or any lateral roots further than 300 mm from the base of the stem. This suggests that either the roots do not experience the stresses required to induce compression wood formation, or that they lack the ability to form it. Roots artificially subjected to mechanical stress also failed to develop compression wood. It is therefore unlikely that an absence of a compressive load on buried roots can account for the lack of compression wood. Application of auxin to the cambia of lateral roots was similarly ineffective at inducing the formation of compression wood. These observations suggest that the buried roots of radiata pine lack the ability to develop compression wood. We also report the formation of an atypical S3 wall layer in the mechanically-stressed and auxin-treated tracheids and suggest that a reaction wood that is different to compression wood may well form in roots.