International Research Group (IRG) on Wood Protection
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ItemOn the occurrence of Phialophora species in preservative treated wood in ground contact(1977)Phialophora is a fairly large genus comprising about thirty described species. They are widespread in very diverse environments, such as soil, sea water, wood and wood pulps. Some species are known as parasites on plants and animals, including man. Phialophora species were early known for their ability to produce blue stain in timber. Later it was discovered that several species were able to produce soft rot in wood. After the presentation of several papers given in Berlin 1975 at the symposium "Organisms and Wood" and the subsequent discussions at the meeting of the IRG/WP in Jadwisin, Poland the same year, it became obvious that species of Phialophora were important in the biodegradation of wood and preservative treated wood in particular. It was decided to give more attention to this group of fungi. Phialophora hoffmannii was mentioned as especially important. No papers on this item were presented at the 8th IRG meeting in Switzerland in 1976. However, the discussions as to the importance of the Phialophora species were continued. The present paper is an attempt to compile information concerning the occurence of various Phialophora species from our own studies in Sweden and from the existing literature. The material investigated in Sweden consisted of preservative treated test stakes and posts as well as electricity and telegraph poles in service. The main contribution, however, comes from a specially designed study, where posts of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) were v/p-treated with a CCA-preservative and installed in two different test fields in Sweden.
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ItemCollaborative field experiment: Analysis of copper and chromium in stakes of the four reference timbers(1982)The stakes analysed belong to the Swedish set of the four reference timbers of the collaborative field experiment (Document No: IRG/WP/367). Before the field exposure 60 mm were cut off the end of each stake. This was done in order to be able to carry out chemical analyses as well as different types of testing. Some of the material has been used in softrot tests (Document No: IRG/WP/1151).
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ItemDecay patterns observed in butylene oxide modified ponderosa pine after exposure in unsterile soil(1982)Small blocks of ponderosa pine (Pinus ponderosa Laws) chemically modified with butylene oxide to three different weight gains were exposed for 6 weeks in unsterile soil. Severe surface decay caused by soft rot fungi and tunnelling bacteria was observed in blocks with 8 weight percent gain. The soft rot attack was restricted to the outer parts of the radial walls in the latewood tracheids. Bacterial attack occurred both in the radial and tangential walls. Very few soft rot cavities were found in blocks with 15 weight percent gain. Some attack by tunnelling bacteria was observed in the outermost parts of the radial walls in the latewood tracheids. Wood blocks with 23.7 weight percent gain showed no signs of attack. A solution of crystal violet was used for examining pathways in ponderosa pine wood. The results indicate that the uneven distribution of cavities is due to improper penetration of the modifying agents into the outer parts of the radial walls in the latewood tracheids.
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ItemComments on soft rot attack in timbers treated with CCA preservatives: A document for discussion(1982)This paper is not based on any particular results but rather on several observations of soft-rot during many years of studies, and on a review of the existing literature. The short time available has unfortunately not permitted a detailed review of the literature. Data and knowledge of important facts are lacking for several aspects of soft-rot attack and for reactions occurring in the wood as a result of the treatment with CCA preservatives. This has made several assumptions necessary and a number of suggestions are being made which are not backed up by results. But this document may nevertheless provide a basis for discussions. Hypothesis: (1) Soft rot attack in low susceptibility wood species is prevented at CCA levels which are too low for preventing growth of soft-rot fungi. (2) High susceptibility hardwood species are only temporarily protected by high retentions of CCA. The concentrations of CCA required are so high that they will be expected to considerably effect the grawth of soft-rot fungi. (3) Formation of T-branches is induced by a chemical factor, most probably of carbohydrate nature, in the wood cell walls. (4) The number of sites where this chemical factor occurs is depending on the carbohydrate/lignin ratio. Few sites occur in high lignin timbers whereas a high number of sites can be expected in low lignin timbers. (5) CCA treatment masks or modifies the sites so that the penetrating hyphae are unable to detect them. The masking is complete in timbers with a high lignin content whereby soft-rot attack is prevented. Only partial masking occurs in hardwoods with a low content of lignin which will allow soft-rot attack to occur. But the soft-rot decay rate is such hardwoods treated to high retentions of CCA will be reduced because of the toxic effects of the preservative.
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ItemInfluence of variable lignin content amongst hardwoods on soft-rot susceptibility and performance of CCA preservative(1982)This paper presents the outline of an argument, based on both new and established data, which relates varying lignin content to variation of soft-rot susceptibility between hardwood species and of performance of CCA preservatives in controlling soft-rot. Although more data need to be generated to prove this relationship, sufficient evidence exists for the hypothesis to be given close attention, particularly as it may provide the link between previous and apparently conflicting theories which attempted to explain the disparate performance of CCA in hardwoods. There are some difficulties in presenting the argument in logical sequence at this stage, so the approach taken has to follow the sequence of events which led to the present conclusions. The paper should therefore be considered as a preliminary draft which may be subject to modification especially as it does not follow a conventional format.
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ItemTunnelling bacteria(1983)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.
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ItemFormation of soft rot cavities in relation to concentric layers in wood fibre walls(1983)A large number of timber species attacked by soft rot have been examined using light microscopy. The S2 layers in a large number of the timbers exhibited special structural features in the form of thin concentric layers. Several observations indicate that these layers may be characterised as "weak" zones by being more easily degradable than the surrounding wall layers. The chemical structure of the concentric layers is not known although some suggestions regarding their composition are given. It was observed that soft rot cavities regularly formed in the thin concentric layers. A hypothesis is put forward suggesting that T-branching occurs as a response to a chemical stimulus, possibly by sugars released by penetrating hyphae when they transverse the thin concentric layers.
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ItemMicromorphology of Schizophyllum commune attack in pine (Pinus sylvestris) wood(1983)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.
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ItemDecay patterns observed in butylene oxide modified ponderosa pine attacked by Fomitopsis pinicola(1983)Small blocks of ponderosa pine chemically modified by butylene oxide to three different weight percent gains (WPG) were decayed for 2 months with the brown rot fungus Fomitopsis pinicola. Wood substance loss and the type of decay pattern recognised were fairly similar both for control and blocks treated to 8 and 15 WPG. No difference in attack was observed between radial or tangential walls in latewood tracheids. Microscopical examination of undecayed wood blocks treated to 23.7 WPG revealed numerous cracks in both the middle lamella regions of radial walls and in cell corners of latewood tracheids. The fungus had gained entry to the cracks, possibly via bordered pits and rays. Attack started from the cracks and progressed along the middle lamella and towards the cell lumen.
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ItemCavitation bacteria(1984)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.