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A summary of current information on actinomycetes and wood
1978 - IRG/WP 177
B King, R A Eaton, A A W Baecker

Micromorphology of the decay caused by Chondrostereum purpureum (Pers.:Fr.) Pouzar and Flammulina velutipes (Curt.:Fr.) Singer
1988 - IRG/WP 1358
Two basidiomycetes, Chondrostereum purpureum and Flammulina velutipes, form typical soft rot cavities in hardwoods and softwoods. Cavity formation is prececed by T-branching or bending of hyphae penetrating the wood cell walls. The two fungi also cause erosion of the wood cell walls.
T Nilsson, G F Daniel

Novel observations on the micromorphology of soft rot attack of wood
1996 - IRG/WP 96-10176
Electron microscopic examinations of decaying Pinus radiata horticultural posts which had been treated with CCA preservative prior to being placed in service about nine years ago showed the presence of soft rot fungi and tunnelling bacteria. Some novel observations on the micromorphology of the soft-rotted areas of tracheid walls are described here. The micromorphology of soft-rotted areas was highly variable. In some areas soft rot cavities were associated with little or no dense residues, whereas in other areas a considerable amount of dense residues was seen around cavities. The dense soft-rotted regions appeared regular in some cases but irregular in others, depending upon the extent to which the tracheid wall around soft rot cavities had been modified. The observed morphological appearance of soft-rotted zones suggests that the initial fungal activities during soft rot attacks of wood cell walls may involve production of molecules small enough to diffuse through the microcapillaries of lignified walls, and in this respect some types of soft rot attack appears to be similar to brown rot attack.
A P Singh, R N Wakeling

Micromorphology of Schizophyllum commune attack in pine (Pinus sylvestris) wood
1983 - IRG/WP 1184
The decay pattern caused by Schizophyllum commune in pine latewood tracheids was studied using both light and transmission electron microscopy. The attack began as isolated concentric slits within the S2 layer with extensive lamellation and separation of individual wall layers observed in subsequent stages of decay. The slits resulting from attack appeared to be formed in thin, regular concentric layers as observed in sound tracheids. This form of attack indicates that the S2 layer is not homogeneous with respect to chemical composition. As the degradation of the S2 layer was caused by hyphae growing within the tracheid lumina, this suggests that diffusion of degrading agents must have occurred through the wall layers.
T Nilsson, G F Daniel

Cytoplasmic and extracellular localization of manganese II dependent peroxidase(s) in white rot fungi during degradation of woody materials
1989 - IRG/WP 1416
The manner by which lignin is degraded in-situ in natural substrates by white rot fungi still remains a controversial issue particularly the distribution and role(s) played by lignin degrading enzymes (i.e. manganese II peroxidase and lignin peroxidase). In the present study, use was made of anti-manganese II peroxidase and immunolabelling techniques in conjunction with transmission electron microscopy (TEM) to study the spatial distribution of manganese II peroxidase during degradation of wood and woody fragments by Phanerochaete chrysosporium and Lentinus edodes. Intracellularly, manganese II peroxidase was found localized in the peripheral regions of the fungal cell cytoplasm in association with both the outer cell membrane and membranes within characteristic vesicular bodies. In addition the enzyme was frequently found localized at the interfacial regions of the cell membrane and inner fungal cell wall. Using double immunolabelling procedures and in addition anti-lignin peroxidase, the cytoplasmic distribution of the two lignin degrading enzymes was compared. Both enzymes showed a fairly similar peripheral cytoplasmic localization although manganese II peroxidase tended to be more concentrated compared to lignin peroxidase in peripheral vesicular bodies. Extracellularly, and in solid wood samples manganese II peroxidase was found localized in all wood cell wall regions of either Betula verrucosa, Populus sp. or Fagus sylvatica decayed by either Phanerochaete chrysosporium or Lentinus edodes at both early and late stages of degradation. In particular, manganese II peroxidase was localized in characteristic zones of degradation produced within the secondary wood cell wall regions. These regions displayed a more open structure compared to unattacked wood cell walls and were easily penetrated by lignin degrading enzymes as judged by infiltration and double immunolabelling studies with highly purified and partially purified manganese II and lignin peroxidases. With Lentinus edodes a very characteristic pattern of lignin degradation was noted in which the middle lamella regions between wood cells was selectively degraded. In these regions manganese II peroxidase was found concentrated and associated with its degrading matrix. An extracellular distribution of manganese II peroxidase associated with wood fragments was also observed in liquid cultures of Phanerochaete chrysosporium grown under conditions optimal for peroxidase production. Despite the immersed conditions, similarities between the patterns of attack and extracellular distribution of the enzyme as for solid wood were noted. With both solid wood and wood fragments, manganese II peroxidase penetration was restricted to regions showing structurally modification, and penetration into undecayed cell walls was not observed. The present work suggests a close substrate-enzyme association during wood cell wall and lignin degradation under natural conditions, and in addition, a close correlation between changes in the micromorphology of decay and manganese II peroxidase distribution. Possible reasons for the failure of previous and similar immunolabelling studies to show such a correlation with lignin degrading enzymes are briefly discussed.
G F Daniel, B Pettersson, T Nilsson, J Volc

Tunnelling bacteria
1983 - IRG/WP 1186
The micromorphology of decay in wood caused by a certain group of single-cell bacteria, called tunnelling bacteria (TB), is described. TB are characterised by their tunnelling ability within the secondary cell walls of wood fibres. Pure cultures of TB have not yet been obtained although the typical decay patterns can be reproduced using mixed bacterial cultures. Some indications of lignin degrading ability by TB have also been found. Laboratory studies indicate that TB are able to attack a wide variety of wood species which are more or less resistant against other forms of decay, either because of preservative treatment, chemical modification, high lignin content or presence of natural toxic extractives. Little information exist at present on the importance of TB for timbers in the field. Most reports are concerned with TB decay of wood in marine or fresh water environments.
T Nilsson, G F Daniel

Micromorphology of decay in Keruing heartwood by the basidiomycetes Phellinus contiguus and Dacrymyces stillatus
2002 - IRG/WP 02-10454
This study aimed to characterise the micromorphology of fungal decay in a wooden handrailing in an above ground exposure at the Thames embankment in London. Keruing heartwood (Dipterocarpus spp.) was determined as the construction timber and the two basidiomycetes Phellinus contiguus and Dacrymyces stillatus identified as main decay organisms. Their decay patterns within Keruing heartwood were studied using light microscopy. Besides typical white and brown rot decay features the analysis also revealed cavities in the fibre S2 wall layers. A laboratory screening test with monocultures of both fungi confirmed their individual ability to form rhomboidal shaped cavities similar to those commonly associated with “true” soft rot fungi. This form of attack indicates that typical soft rot-like cavities can also be formed by white and brown rotting basidiomycetes facultatively and are therefore not an absolute indication for the occurrence of soft rot causing asco- and deuteromycetes respectively.
G Kleist, M Ray, R J Murphy

Cavitation bacteria
1984 - IRG/WP 1235
A form of bacterial wood degradation is described. The term "cavitation bacteria" has been coined in order to describe the discrete cavities that are formed within the wood cell walls. The bacteria observed within the cavities appeared to be polymorphic with rounded as well as filamentous forms recognised. TEM studies suggest that the bacteria produce diffusable wood-degrading enzymes. Cavitation bacteria have been found to be widespread in CCA-treated pine posts in horticultural soils in New Zealand. Significant decay due to cavitation bacteria was observed in a large number of the posts.
T Nilsson, A P Singh

New Observations and Interpretation for Tunnelling Bacteria Decay
2006 - IRG/WP 06-10579
Decay micromorphology was studied systematically for diversely preservative treated Pinus radiata and Fagus sylvatica 20 x 20 x 500 mm stakes across 13 in-ground field test sites, during a 6.5 year exposure. Sites were selected to maximise occurrence of a diverse range of decay types. Micromorphology that suggested orientation of tunnelling bacteria with the cellulose microfibrils of the S2 and S1 cell wall layers was common, an observation that is not consistent with the bulk of the information contained in the literature. This suggested that contrary to current theory, tunnelling bacteria are profoundly affected by the fine ultrastructure of wood (e.g. microfibrils, lamellae and layer infaces). Departures from profound wood cell wall ultrastructure effects on micromorphology, such as apparently random tunnelling, are probably a response to an exogenous stimulus i.e. other than degradative biochemistry and wood ultrastructure. For tunnelling bacteria such a third stimulus might include the putative avoidance mechanism reported by other workers in the field. In addition, it is to be expected that micromorphological patterns produced by a unicellular microorganism would be affected by regular cell division, this being absent for filamentous fungi. Therefore, the often reported micromorphology patterns for tunnelling bacteria might primarily be due to regular cell division coupled with avoidance, two events that would cause a departure from the patterns caused by cell wall ultrastructure. A putative bacterial penetration mechanism purported that a bacterium undergoes rhythmic apical elongation and subsequent distal shortening. Apical extension, elongation and narrowing of the bacterium occurs until the finite volume of the bacterium causes the distal region to break away from its temporarily fixed location, leaving behind a cross wall. This mechanism seems more likely than the previously reported formation of cross walls following complete immobility of the whole bacterium, a behaviour that does not fit with classical understanding of vegetative bacteria. The new hypothesis presented also fits with the enormous plasticity exhibited by tunnelling bacteria during cell wall penetration as shown in TEM micrographs i.e. it is likely that this ability would be further exploited during ongoing formation of tunnels, along paths of minium resistance where possible.
R Wakeling

Micromorphology of Bamboo Fibers Degraded by Brown-Rot Fungus Gloeophyllum trabeum
2006 - IRG/WP 06-10576
The decay pattern of bamboo by brown-rot fungus was examined. In addition, the influence of polylaminate structures in bamboo fibers on the restriction of fungal decay was also investigated. The weight loss of bamboo Phyllostachys puberscens by the brown-rot fungus Gloeophyllum trabeum after 16 week incubation was about 25%. Parenchyma cells were severely degraded. Microscopical studies showed that G. trabeum removed the inner part of multi layers while the last layer in the polylaminate secondary walls, corresponding to S3 layer in the tracheids, remained essentially intact. Bamboo fiber walls were degraded at a considerable distance from fungal hyphae. Main decomposition of bamboo fiber cell wall by G. trabeum was similar to other brown-rot fungi in terms of preferential removal of inner part of secondary walls, remaining the last layer in polylaminate layer intact. Cytochemical work showed the production of hydrogen peroxide by the brown-rot fungus G. trabeum and the diffusion into the bamboo fiber walls. The effect of polylaminate structures and lignin levels at the narrow layers on restriction on fungal decay to bamboo fibers was also discussed.
Kwang Ho Lee, Chang Hyun Cho, Yoon Soo Kim

Common Decay Micromorphology “Anomalies” Challenge Current Decay Classification
2006 - IRG/WP 06-10578
Decay micromorphology was studied systematically for diversely preservative treated Pinus radiata and Fagus sylvatica 20 x 20 x 500 mm stakes across 13 in-ground field test sites, during a 6.5 year exposure. New insight into the micromorphology of the early stages of decay enabled new and more detailed interpretation of the mechanism of their formation and suggested that current decay classification lacked sufficient robustness to accommodate common decay types encountered in field-exposed wood. Decay fungi that bypass the decay resistant S3 layer, producing multi-branched hyphae that collectively erode the S2 layer in a fashion similar to simultaneous white rot, forming a “super-cavity” under an overlying lumen wall, were very important in preservative treated beech fibres and pine tracheids. Whilst some of the micromorphology associated with this type of decay has been reported as diffuse type 1 soft rot, its significance has been largely overlooked. Results suggested that several important decay types have been overlooked or misinterpreted because their early defining features are easily masked by later features. This is particularly important for early cavitation decay that forms near or at the S3-S2 interface, and where the overlying lumen wall quickly disintegrates, has been sloughed off during sectioning or has been overlooked in low resolution light microscope micrographs. It is suggested that this has resulted in misinterpretation of cavitation decay types as erosion (Corbett’s type 2, erosion). Use of transmission electron microscopy (TEM) for examining decayed wood has relied heavily on transverse sections or use of high magnification, both of which would mask critical diagnostic features such as intact lumen wall in combination with longitudinally sectioned hyphae both of which are needed for diagnosis.
R Wakeling

Evidence for Basidiomycete Tunnelling in Pinus radiata and Fagus sylvatica
2006 - IRG/WP 06-10587
Decay micromorphology was studied systematically for diversely preservative treated Pinus radiata and Fagus sylvatica 20 x 20 x 500 mm stakes across 13 in-ground field test sites, during a 6.5 year exposure. Sites were selected to maximise occurrence of a diverse range of decay types. Presence of clamp connections in close associated with tunnelling coupled with macroscopic features similar to white rot was a strong indication that white rot basidiomycetes were the causative agents of hyphal tunnelling. Hyphal tunnelling is a fungal decay type that does not fit neatly within the decay types brown rot, soft rot (Types 1, 2 and diffuse) and white rot (simultaneous and preferential). Overly rigid decay classification boundaries that place emphasis on taxonomic affinity and biochemical reactions under laboratory conditions, fail to accommodate the diversity of decay types that occur under field conditions. Classical simultaneous white rot and type 2 erosion soft rot were almost completely absent from preservative treated pine and beech across 13 highly diverse sites. It is possible that fungal erosion decay was of minor significance in preservative treated wood because the decay fungi that cause it in other situations (e.g. in untreated wood) adopt a tunnelling or cavitation mode in preservative treated woods i.e. they adopt a stress tolerant strategy in response to the high lignin content and/or preservative content of the lumen wall. It is known that some basidiomycetes produce cavitation with features very similar to soft rot cavitation and this study and the work of others indicates that basidiomycetes also produce a mixture of features typically associated with soft rot and those fungi which produced hyphal tunnelling. It is possible that some of these basidiomycetes possess multiple decay capabilities.
R Wakeling

Confocal laser scanning microscopy of a novel decay in preservative treated radiata pine in wet acidic soils
1997 - IRG/WP 97-10215
Light microscopy of radiata pine (Pinus radiata D. Don) field test stakes (20x20x500mm3) exposed in wet acidic (pH 3-4) soil for 12 - 24 months showed predominance of an unusual type of decay characte-rised by tunnelling attack of wood cell walls. After two years decay was moderate to severe in wood treated to ground contact CCA specifications and also equivalent retentions of creosote, and a number of new generation preservatives. Relative to other New Zealand temperate test sites and also an Australian tropical site, the New Zealand acidic soil test site was very aggressive. Correlative scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to elucidate the micromorphology of this attack. Tunnels of diameter 0.2-5 µm were present throughout all layers of the cell wall, and their orientation was not related to cellulose microfibril orientation. They also showed no preference for particular cell wall layers, indicating a lignin degrading capability. CLSM images showed that living, connecting fungal hyphae were present in the cell lumina and tunnels. This type of attack was predominant in wood that was highly saturated with water whereas wood that was less moist was predominantly attacked by classical white rot. Ongoing isolation and incubation studies in conjunction with further microscopy should enable identification of the fungal species involved.
R N Wakeling, Ying Xiao, A P Singh

Effect of acetylation on decay resistance of wood against brown-rot, white-rot and soft-rot fungi
1989 - IRG/WP 3540
Effect of acetylation on decay resistance of wood was investigated using wood blocks of Cryptomeria japonica, Pinus densiflora, Albizia falcata and Fagus crenata. Blocks were treated with uncatalyzed acetic anhydride for different lengths of time and exposed to Tyromyces palustris, Serpula lacrymans, Coriolus versicolor and unsterilized soil. The action of OH-radical on acetylated wood was also examined using Fenton's reagent. The enhancement of decay resistance by acetylation was revealed clearly for all cases of exposures but varying with fungal and wood species used. For a brown-rot fungus Tyromyces palustris, the weight loss reached almost nil in all woods at 20 WPG (weight percent gain) of acetylation, after the striking decrease from 10 to 15 WPG. For a white-rot fungus Coriolus versicolor, it was counted until 12-15 WPG in the perishable hardwoods used, but not in a softwood Cryptomeria japonica, even at 6 WPG. In cases of another brown-rotter Serpula lacrymans and soil burial, effect of acetylation was intermediate between Tyromyces palustris and Coriolus versicolor. Anti-degradation mechanism by acetylation was discussed, from these weight loss - weight gain relationships, and the IR-and 13C-NMR spectral analyses of fungus-exposed wood.
M Takahashi, Y Imamura, M Tanahashi

Field trial with poles of Scots pine treated with six different creosotes
1996 - IRG/WP 96-30115
In the middle of the 50's field trials with creosote-treated poles were started in France, Germany and Sweden. The trials were initiated by WEI (Western-European Institute for Wood Preservation). Six different creosotes were used and 40 poles per creosote were installed at each test field. Results after 39 years of exposure in Simlangsdalen, Sweden are reported. Poles treated with a heavy creosote were less decayed than poles treated with medium-heavy creosotes. Poles treated with a light creosote were most decayed.
Ö Bergman

Questionnaire - Fungal decay types
1985 - IRG/WP 1265
T Nilsson

JWPA method for testing effectiveness of surface coatings with preservatives against decay fungi
1981 - IRG/WP 2164
In 1979 JWPA established a new method for testing effectiveness of surface coatings in accordance with practical use of preservative-treated lumber. Comparing the new testing method with JIS A 9302, a few new trials - size of wood specimen, weathering procedure, and decay-test procedure - are incorporated.
K Tsunoda

Utilization of curcumin for detection of presence of boron in wood
1982 - IRG/WP 3191
It has been shown that curcumin is not a reliable reagent for detecting boron in wood that has been attacked by fungi
M-L Edlund

Co-operative studies on determining toxic values against wood-destroying Basidiomycetes: Progress report to May 1989
1989 - IRG/WP 2339
This document reports progress on the co-operative study between nine laboratories set up following the proposals contained in Document IRG/WP/2316. Results have been received from two laboratories. Toxic values data have been established successfully using the test fungus Coniophora puteana but problems have been encountered with the other test fungi.
A F Bravery, J K Carey

Monographic cards for wood-destroying fungi. [Fiches monographiques pour les champignons lignivores]
1970 - IRG/WP I 5B
C Jacquiot

On Donkioporia expansa (Desm.) Kotl. & Pouzar
1986 - IRG/WP 1285
Donkioporia expansa is found more often in houses than realised until now. Virulence tests according to EN 113 show not only an attack of oak, but also of other hardwoods and even soft-woods.
G Buchwald

Nondestructive Evaluation of Oriented Strand Board Exposed to Decay Fungi
2002 - IRG/WP 02-20243
Stress wave nondestructive evaluation (NDE) technologies are being used in our laboratory to evaluate the performance properties of engineered wood. These techniques have proven useful in the inspection of timber structures to locate internal voids and decayed or deteriorated areas in large timbers. But no information exists concerning NDE and important properties of wood composites exposed to decay fungi. For our pilot study on several types of wood composites, we examined the relationship between nondestructive stress wave transmission, decay rate and the bending properties of OSB exposed to the brown-rot fungus, Gloeophyllum trabeum (MAD-617). The following measurements were taken: stress wave transmission time (pulse echo test method), static bending test (ASTM D3043-95), and decay (expressed as percent weight). Stress wave measurements correlated with strength loss and with increasing rate of fungal decay. Stress wave NDE has great potential as a method for inspection of wood composite load-bearing (in-service) structures, detection of decay in laboratory tests, assessment of chemical additives to improve wood composite durability, and prediction of long term composite performance.
B Illman, V W Yang, R J Ross, W J Nelson

Moisture content levels and decay of hemlock
1986 - IRG/WP 1287
As a model of decay conditions of wooden members in wooden houses, a decay test was set up in which samples of western hemlock (Tsuga heterophylla) under 4 moisture levels were examined. Each week the samples were weighed and if the weights indicated that their moisture contents were lower than the expected levels, distilled water was added. Every 8 weeks 3 samples from each condition were oven dried at 60°C for 48 hours, up to 48 weeks. After 48 weeks, 3 samples from each condition were oven dried every 16 weeks. The results obtained were as follows: After examining the samples for 96 weeks at 27°C, the mean weight loss of the hemlock samples kept at about 50-100% moisture content level was larger than those of the other levels. If the samples were dried every 8 weeks, the amount of decay in them was not significant. Decay was also not significant in the samples kept at approximately 20-30% moisture content level.
K Suzuki

Dimensional stability and decay resistance of hot-melt self-bonded particleboard by surface benzylated pine chips
1991 - IRG/WP 3652
Akamatsu (Pinus densiflora Sieb. et Zucc: Japanese red pine) particles were pretreated with 40% NaOH solution and benzylated with benzyl chloride, and the surface of particle was converted into meltable materials. Hot-melt self bonded particleboard having smooth and high glossiness surface was prepared by hot pressing at 150°C and 1.96 MPa without using any conventional adhesives. Dimensional stability and decay resistance of the benzylated particleboard were evaluated. Particleboards made of benzylated particles having more than 38% of weight percent gain (WPG) showed that dimensional stability and decay resistance were superior to the conventional particleboard made by using phenolformaldehyde resin as a binder, because hydroxyl groups of wood were substituted by hydrophobic benzyl groups with benzylation. Though bending strength of the board was a little lower than control board due to the damage of benzylated particles during benzylation, its internal bonding strength was very high, because the hot-melting strengthened the inter-particle bonding.
M Kiguchi, K Yamamoto

How to Document the Performance of Super-Critical Treated Wood in above Ground Situations?
2005 - IRG/WP 05-20316
The paper presents practical experiences from the preparation of a new preservative treated wood product for introduction to the market. The product in question is Superwood™, which is treated with organic biocides using CO2 in a supercritical state as a solvent. The question is how to evaluate the performance of a new product such as Superwood™ in order to get an acceptance on the market and fulfil the formal requirements. In the European Union countries, the EN 599-1 is the standard that needs to be complied when approving a new product for the market, but it only focuses on the toxic limit against representative decay fungi according to EN 113. However, decay test, above ground and other forms of field tests are optional, this is not in line with the traditional test philosophy in the Scandinavian countries. The open question is to which extent treatment to the level of the toxic threshold value also ensures a long service life and expected performance of the treated commodity. Superwood™ is evaluated using a strategy, in which basic laboratory tests are done to get the toxic value (according to EN 599-1) and in addition a number of field tests are done including accelerated testing in the tropics. These tests are focussed on the evaluation of the performance criteria such as durability and service life and maintenance requirements. These questions must be answered by the producer without having a full record of performance test for their new products. A short status on the test performed on super-critical treated wood (Superwood™) is presented. Based on a comparison between field test in Scandinavia and in the tropical Malaysia a service life of more than 25 years for a specific supercritical treated product is estimated. It is stated that the existing European standardisation system is insufficient when it comes to service life prediction. A number of important questions need to be addressed by the European standardisation system as soon as possible because the market and the public opinion change quickly due to environmental concern.
N Morsing, A H H Wong, F Imsgard, O Henriksen

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