Three Gram negative bacteria isolated from brownstained western hemlock were investigated for their capacity to produce hemlock brownstain. Brownstain was observed when infecting western hemlock with two bacteria. Oxygen was strongly indicated as being indespensable for the development of brownstain in infected samples. However, pH did not seem to influence the production of this stain.
Discolourations of hem-fir, usually called hemlock brownstain, have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolourations cannot be tolerated. These discolourations, clearly different from sapstain, can occur in several types and intensities and are a serious problem in high-value markets. Because little is known about their causes means for their control are still unavailable. Therefore fundamental research was initiated to elucidate the biology and chemistry of hemlock brownstain and to suggest control measures. A post graduate student was hired to undertake laboratory and field work as part of a Ph.D. program. The thesis subject was "the role of microorganisms in the phenomenon of hemlock brownstain". The thesis covers: a literature review; laboratory work to locate the stain and define its nature; a storage study of logs and lumber to monitor progress in development of brownstain; fungal isolation work and sap characterization studies; in vitro production of hemlock brownstain in wood and sap; and additional laboratory experiments to determine what factors influence the formation of the brownstain. In addition to the thesis research the role of bacteria in the formation of the stain was investigated in the laboratory and the ability of various chemicals, including fumigants, to prevent the stain was tested in small-scale field test. This report provides an overview of the findings and provides recommendations for future work. The experiments clearly demonstrated that a non-specific microflora can produce brownstain which led to the hypothesis that microorganisms could be involved in hemlock brownstain. Based on our knowledge of the coastal sawmilling industry a strategy of minimizing fungal infection and rapid handling of the tree breakdown into final wood products could probably be the best approach to help reduce the problem. In terms of future work we recommend that work to understand the mechanism of DDAC in mitigation of the browning take precedence in future work on hemlock brownstain.
The natural wood appearance of many species can be affected by a variety of undesirable "non-microbial" discolourations, which reduce the value of wood products. In contrast to sapstain, caused by fungi, prevention of these discolourations has rarely been demonstrated in practice. Discolourations of hem-fir have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolourations are less tolerable. A literature review was done to survey both general information on "non-microbial" discolourations and more specifically information on discolourations of western hemlock and amabilis fir. Although discolouration of hem-fir lumber has been a puzzle for many years, knowledge of its cause(s) is rudimentary. Most research into hem-fir discolourations has been conducted on only a few wood samples. Although polymerization of wood extractives has been proposed as the probable cause, involvement by bacteria and fungi are also suggested in the literature. Other factors involved in discolourations of other wood species, such as factors inherent in the living tree, season of tree felling, post mortem changes and log age and storage, are reviewed. The nature of specific wood extractive chemicals and the significance of other contributory factors need to be understood before preventive treatments can be devised to maintain the natural colour in hem-fir products. Research recommendations include microscopic and histochemical techniques.
Microscopic examinations were conducted on discoloured hem-fir samples indicating different types of "brownstain" patterns. Distribution of "brownstain" discolouration in hem-fir lumber is variable. Microorganisms were found in all specimens examined. The role of microorganisms in "brownstain" discolourations needs to be elucidated. Research recommendations include monitoring of biological and chemical changes of freshly sawn hem-fir lumber over time.
Hemlock brownstain was studied histochemically, in microscopic sections of western hemlock and amabilis fir, and chemically, using wood extractives of western hemlock. For the first time it was histochemically demonstrated that brown pigments, found in amabilis fir and western hemlock, are at least partially composed of catechin and/or epicatechin. Evaluation of nine extractives of western hemlock provided no indication that they play a significant role in hemlock brownstain. However, sap collected from western hemlock showing signs of brownstain produced browning on filter paper. Thus the composition of the sap, yet unidentified, was responsible for discolouration observed in this study.
Biological and chemical changes were evaluated in freshly sawn amabilis fir and western hemlock lumber (hem-fir) over 10 weeks of outside storage. Both wood species commonly contained brownstain microscopically in heartwood and sapwood. Microorganisms were often found in discoloured samples, but brownstain could not be linked to the presence of microorganisms. Qualitative HPLC analysis was employed on methanol extracted hem-fir segments over time, but this approach provided no indication about potential precursors to hemlock brownstain. However, the HPLC method developed produced a reliable separation and identification of nine wood constituents in hem-fir lumber and can be used for future quantitative analysis. The factors producing macroscopic brownstain were not understood, but a high moisture content appeared to be essential to transport precursors of hemlock brownstain to the wood surface.
Three strains of Ophiostoma piceae (Münch) H. & P. Syd. and a mixed bacterial culture were studied for their potential to produce in vitro brownstain in sap of amabilis fir, western hemlock and lodgepole pine and in western hemlock wood. Several microorganisms increased the pH of all sap samples evaluated and a distinct brown discolouration developed in sap of western hemlock and amabilis fir over 3 weeks. Although pH shift influenced brown discolourations of sap, nutrient status and the extractive composition of the sap appeared to be critical for promoting browning of sap. O. piceae strains also produced brown discolourations in sapwood of western hemlock but the mixed bacterial culture caused minor brown staining only. While we have demonstrated a link between microorganisms and brownstain in liquid culture more research is needed to understand susceptibility of amabilis fir and western hemlock lumber to brown discolourations.
A range of moulds and sapstaining fungi produced in vitro brownstain in sap collected from three different western hemlock boards. Colour changes varied among both microorganisms and source of sap used. However, a link has been established between microorganisms and their potential to cause pH changes in sap; the pH seemed to promote discolourations. However, both the susceptibility of sap to discolourations and the mechanism of colour changes have not yet been elucidated.
The natural wood appearance of many species can be affected by a variety of undesirable "non-microbial" discolorations, which reduce the value of wood products. In contrast to sapstain, caused by fungi, prevention of these discolorations has rarely been demonstrated in practise. Discolorations of hem-fir have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolorations are less tolerable. A literature review was done to survey both general information on "non-microbial" discolorations and more specifically information on discolorations of western hemlock and amabilis fir. Although discolorations of hem-fir lumber have been a puzzle for many years, knowledge of their cause(s) is rudimentary. Most research into hem-fir discolorations has been conducted on only a few wood samples. Although polymerization of wood extractives has been proposed as the probable cause, involvement by bacteria and fungi are also suggested in the literature. Other factors involved in discolorations of other wood species, such as factors inherent in the living tree, season of tree felling, post mortem changes and log age and storage are reviewed. The nature of specific wood extractive chemicals and the significance of other contributory factors need to be understood before preventive treatments can be devised to maintain the natural color in hem-fir products. Research recommendations include microscopic and histochemical techniques.
Mechanical tree harvesters damage the exterior of freshly felled logs, loosening and removing bark, and producing punctures and indentations up to several centimeters deep. Damaged logs are susceptible to invasion by a plethora of wood inhabiting fungi. In this study, we investigated the role of tree harvesters in disseminating fungi, particularly wood-discoloring fungi, or inoculating Canadian lodgepole pine and New Zealand radiata pine logs.
In the study reported here wood decaying fungi, staining fungi and moulds were isolated from a harvester head and the bark of standing lodgepole pine trees. This microflora may be translocated into the sub-surface regions of a log during the harvesting process. In Canada, Aureobasidium pullulans was the most frequently isolated staining fungus followed by Ophiostoma minus and Leptographium sp. All were isolated from stained areas associated with damage sites. Sphaeropsis sapinea was the most prominent species in New Zealand. Tree harvesters clearly play a role in the dissemination of wood degrading fungi into freshly felled conifer logs.