Naturally durable heartwood: evidence for a proposed dual defensive function of the extractives

We previously proposed that extractives in highly durable heartwood may protect wood against fungal colonization and subsequent degradation by dual mechanisms: the extractives have some fungicidal activity and are also free radical scavengers (antioxidants). In short-term laboratory decay tests using two different wood species and decay fungi, the antioxidant 2,6-dimethyl-di-tert-butyl-4-methylphenol (BHT) alone had little or no preservative effect. In contrast, the combination of BHT with different organic commercial biocides always showed an increase in efficacy compared to the organic biocide alone. Consequently, we conclude that the combination of a commercial antioxidant and biocide is synergistic. This implies that extractives may protect wood by more than simply being fungicidal.     

Evaluation of antifungal properties of octyl gallate and its synergy with cinnamaldehyde

The objective of this study was to investigate the possibility of using octyl gallate alone or with organic biocides as a preservative against wood decay fungi. Antifungal activities of three antioxidants, propyl gallate, octyl gallate and butylated hydroxyltoluene (BHT) were tested against four wood decay fungi, Lenzites betulina, Trametes versicolor, Gloeophyllum trabeum and Laetiporus sulphureus. Octyl gallate was found to be the only active compound with IC50 values of 0.47, 0.16, 0.24 and 0.04 mM against L. betulina, T. versicolor, G. trabeum and L. sulphureus, respectively. A synergistic effect was also found when octyl gallate was combined with cinnamaldehyde. Results obtained herein demonstrated that octyl gallate by itself exhibited an excellent antifungal property and enhanced protection was further observed by combining it with cinnamaldehyde.     

Antioxidants and iron chelators inhibit oxygen radical generation in fungal cultures of plant pathogenic fungi

Eutypa dieback and Esca are serious fungal grapevine trunk diseases (GTDs). Eutypa dieback is caused by Eutypa lata (Elata), and is often associated Phaeoacremonium minimum (Pmin), and Phaeomoniella chlamydospora (Pch) which are also important contributors to Esca disease.Understanding the complex pathogenesis mechanisms used by these causative fungi may potentially lead targeted treatments for GTDs in the future. Elata has been reported as a wood decay “soft rot” fungus and understanding of Elata’s pathogenesis chemistries can aid in controlling GTDs. Recent work that suggests that Pmin and Pch may contribute to pathogenesis by stimulating hydroxyl radical generation via secretion of low molecular weight phenolic metabolites. Building on these findings, we tested a hypothesis that antioxidants and chelators, and biocontrol agents that have been reported to secrete antioxidants and low molecular weight chelators, may inhibit the growth and activity of these fungi. Butylated hydroxy anisole (BHA) and butylated hydroxytoluene (BHT) were tested as antioxidant/chelators. BHA was found to be a highly effective control measure for the three pathogenic fungi tested at concentrations >0.5 mM. The biocontrol species Bacillus subtilis and Hypocrea (Trichoderma) atroviride were also tested, with both H. atroviride and B. subtilis effectively inhibiting growth of the three GTD fungi.     

Decay resistance of wood treated with boric acid and tall oil derivates

In this study, the effect of two boric acid concentrations (1% and 2%) and four derivates of tall oil with varying chemical composition were tested separately and in combination. The tall oil derivates were chosen in a way that they consist of different amounts of free fatty, resin acids and neutral compounds. Decay tests using two brown rot fungi (Postia placenta and Coniophora puteana) were performed on both unleached and leached test samples. Boric acid showed a low weight loss in test samples when exposed to fungal decay before leaching, but no effect after leaching. The tall oil derivates gave better efficacy against decay fungi compared to control, but are not within the range of the efficacy needed for a wood preservative. Double impregnation with boric acid and tall oil derivates gave synergistic effects for several of the double treatments both in unleached and leached samples. In the unleached samples the double treatment gave a better efficacy against decay fungi than tall oil alone. In leached samples a better efficacy against brown rot fungi were achieved than in samples with boron alone and a nearly similar or better efficacy than for tall oil alone. Boric acid at 2% concentration combined with the tall oil derivate consisting of 90% free resin acids (TO-III) showed the best performance against the two decay fungi with a weight loss less than 3% after a modified pure culture test.     

Protecting wood from mould,decay, and termites with multi-component biocide systems

Biocides must be developed for controlling mould establishment on cellulose-based building materials. Accordingly, biocides intended for indoor applications must be non-toxic, non-volatile, odourless, hypoallergenic, and able to provide long-term protection under conditions of high humidity. Multi-component biocide systems were tested in American Wood-Preservers’ Association soil block tests for inhibition of brown-rot and white-rot decay fungi and American Society for Testing and Materials standard tests for inhibition of mould fungi and termites. Multi-component systems combining a borate base supplemented with either 0.1% azole or 0.5% thujaplicin, performed well against the two brown-rot fungi Postia placenta and Gloeophyllum trabeum; the white-rot fungus Coriolus versicolor; the three mould fungi Aspergillus niger, Penicillium chrysogenum, and Trichoderma viride; and the subterranean termite Reticulitermes flavipes (Kollar). It was concluded that for interior applications borate-based multi-component biocide systems can protect wood from decay fungi, mould fungi, and termites, and that a system containing thiabendazole provided protection at a lower retention than the other biocides in this study. Synergy was observed between the borate base and voriconazole in inhibition of mould.     

Activity of dehydroabietic acid derivatives against wood contaminant fungi

The antifungal activity of 10 dehydroabietic acid derivatives with different configuration in A and B rings (cis/trans A/B junction) and different substituents and/or functionalities was evaluated in bioassays in vitro and in situ (pine wood blocks).

The test compounds dissolved in acetone were assayed at several concentrations w/w (test compound/culture medium) against the fungi. The Relative Inhibition (RI) was determined by measuring the radial growth of colonies of the fungi treated with the test compounds by comparison with those of control cultures; the results are expressed as EC₅₀.

The results of bioassays in vitro have shown that hydroxyl and aldehyde functions are required for antifungal activity in this group of compounds and deisopropylation can increase the activity. Our assay of antifungal activity in situ (in pine wood blocks) provides a means to investigate the preservative activities of these antifungal compounds under actual conditions of use.

The dehydroabietic acid derivative cis-deisopropyldehydroabietanol (10) inhibited the growth of several of the fungi tested, in vitro and in situ.

The results obtained in situ with the test compound (10) at 6% and 8% were not significantly different from the reference products and a good level of protection of the wood against the organisms tested was achieved.

The results in wood bioassays present new possibilities in the search for natural new compounds in the wood protection, as an alternative to conventional fungicides.     

Wood durability of home-garden teak against brown-rot and white-rot fungi

Natural decay resistance of teak wood grown in home-garden forestry and the factors influencing decay resistance were determined in comparison with that of a typical forest plantation. Accelerated laboratory tests were conducted on 1800 wood samples drawn from 15 trees of three planted sites. Analysis of variance based on a univariate mixed model showed that planted site, fungal species, and their interaction terms were important sources of variation in decay resistance. With increasing decay resistance from centre to periphery of the heartwood, radial position was a critical factor and the interaction effect of fungal species × radial position was significant in influencing the durability. No significant differences were found in decay resistance either between the opposite radii or due to the various possible interaction terms of radii with the site, fungal species and radial position. There were significant differences in decay resistance against brown-rot fungi between wet and dry sites of home-garden teak although differences against white-rot fungi were non-significant among the three planted sites. Polyporus palustris was the more aggressive brown-rot fungus than Gloeophyllum trabeum. The higher susceptibility of wet site home-garden teak to brown-rot decay was associated with a paler colour of the wood and lower extractive content.     

Evaluation of possible decay and termite resistance of particleboard containing waste tire rubber

Particleboard specimens produced by adding waste tire rubber particles were assayed against white- and brown-rot fungi and termites in laboratory conditions. Particleboards were manufactured from a mixture of pine and poplar particles bonded with two different resins (melamine/urea formaldehyde [MUF] and polyisocyanate [PI]) by adding waste tire rubber particles at three different levels (10%/90%, 20%/80%, and 30%/70% by weight of waste tire rubber/wood). The particleboard specimens with waste tire rubber were not generally resistant against four fungi tested. Only MUF-containing specimens showed considerably better performance in decay resistance tests using the brown-rot fungus, Postia placenta; however, addition of waste tire rubber into those specimens did not provide resistance in comparison with control specimens without tire rubber. Formosan termites were also able to degrade particleboard specimens with waste tire rubber.     

Montan wax improves performance of boron-based wood preservatives

Importance of boron compounds in wood preservation is increasing due to their low environmental impact, high efficacy and the fact that many other active ingredients have been removed from the market after the introduction of the Biocidal Products Directive. The most important drawback of boron is prominent leaching in wet environment. In order to improve their fixation, and performance against wood decay fungi, boric acid was combined with montan wax emulsion. Possible synergistic effects of boric acid and montan wax were determined according to modified EN 113 procedure. Norway spruce and beech wood specimens were exposed to three white rot (Trametes versicolor, Pleurotus ostreatus and Hypoxylon fragiforme) and brown rot wood decay fungi (Gloeophyllum trabeum, Antrodia vaillantii and Serpula lacrymans) for 12 weeks. Boron leaching from vacuum/pressure treated Norway spruce wood was determined according to the continuous (EN 84 and ENV 1250-2) and non-continuous (OECD and prCEN/TS 15119-1) procedures. Boron was determined with ICP mass spectrometry in collected leachates. The results of the fungicidal tests clearly showed that montan wax emulsion and boric acid act synergistically against tested wood decay fungi. Approximately 50% lower boric acid retentions are required in combination with montan wax emulsions to achieve sufficient protection against wood rotting fungi. However, it is even more important that all leaching tests performed proved that the addition of montan wax decreased boron leaching from impregnated specimens for 20% up to 50%.     

Exercise,antioxidants, and HSP72: protection against myocardial ischemia/reperfusion

Endurance exercise is associated with protection against myocardial ischemia/reperfusion (I/R) injury and has been shown to increase heat shock protein 72 (HSP72). Dietary antioxidants have also been reported to decrease I/R-induced injury. Because exercise and antioxidants may provide cardioprotection via different mechanisms, combining these countermeasures could provide additive protection. Alternatively, because exercise-induced oxidant production may promote expression of HSP72, antioxidants could attenuate exercise-induced HSP72 expression and decrease exercise-related cardioprotection. These experiments examined the individual and combined effects of exercise and antioxidants on myocardial I/R injury (in vivo). Rats receiving a mixed antioxidant diet or control diet were assigned to exercise or sedentary groups and randomized to receive: (i) short I/R (myocardial stunning), (ii) long I/R (myocardial infarction), or (iii) sham surgery. Antioxidants significantly increased total antioxidant capacity and attenuated exercise-related HSP72 accumulation. Nonetheless, during short I/R, exercise-trained animals demonstrated improved left ventricular developed pressure (LVDP), independent of diet. Further, antioxidants alone resulted in improved LVDP. Finally, compared to control diet/sedentary animals, both exercise groups (control and antioxidant diets) and the antioxidant diet/sedentary group sustained smaller infarctions. We conclude that exercise and antioxidants can independently provide protection against myocardial contractile dysfunction and infarction, and the combination of these two strategies does not enhance or inhibit the protection observed with each individual countermeasure.     

Elucidating wood decomposition by four species of Ganoderma from the United States

The laccate (shiny or varnished) Ganoderma contain fungi that are important wood decay fungi of living trees and decomposers of woody debris. They are also an important group of fungi for their degradative enzymes and bioprocessing potential. Laboratory decay microcosms (LDMs) were used to study the relative decay ability of G anoderma curtisii, Ganoderma meredithiae, Ganoderma sessile, and G anoderma zonatum, which are four commonly encountered Ganoderma species in the U.S., across four wood types (Pinus taeda, Quercus nigra, Q uercus virginiana, and Sabal palmetto). Generally, all Ganoderma species were able to decay all types of wood tested despite not being associated with only certain wood types in nature. G. sessile, on average caused the most decay across all wood types. Among the wood types tested, water oak (Q. nigra) had the most mass loss by all species of Ganoderma. Scanning electron microscopy was used to assess micromorphological decay patterns across all treatments. All Ganoderma species simultaneously decayed wood cells of all wood types demonstrating their ability to attack all cell wall components. However, G. zonatum caused selective delignification in some sclerenchyma fibers of the vascular bundles in palm (S. palmetto) as well as in fibers of water oak. In addition, G. zonatum hyphae penetrated fibers of palm and oak wood causing an unusual decay not often observed in basidiomycetes resulting in cavity formation in secondary walls. Cavities within the secondary walls of fibers gradually expanded and coalesced resulting in degradation of the S2 layer. Differences in colony growth rates were observed when Ganoderma species were grown on medium amended with water soluble sapwood extracts from each wood type. G. meredithiae had enhanced growth on all media amended with sapwood extracts, while G. curtisii, G. sessile and G. zonatum had slower growth on loblolly pine extract amended medium.     

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

Fast-growing bacteria and fungi are expected to cause the initial stage of decomposition of woody fragments in and on soils, i.e. the respiration of sugars, organic acids, pectin and easily accessible cellulose and hemi-cellulose. However, little is known about the factors regulating initial wood decomposition. We examined the effect of wood fragment size, vertical position, nitrogen addition and soil origin on initial wood decay and on the relative importance of fungi and bacteria therein. Two fractions of birch wood were used in microcosm experiments, namely wood blocks (dimensions: 3 × 0.5 × 0.5 cm) and sawdust (dimensions: 0.5–2 mm). The woody fragments were enclosed in nylon bags and placed on top of- or buried in an abandoned arable soil and in a heathland soil. After 15, 25 and 40 weeks of incubation, fungal biomass was quantified (as ergosterol and chitin content) and bacterial numbers were determined. The results indicated that initial wood decay was mostly caused by fungi; bacteria were only contributing in sawdust in/on abandoned arable soil. Larger fragment size, burial of fragments and nitrogen addition positively influenced fungal biomass and activity. Fungal biomass and decay activities were much lower in woody fragments incubated in/on heathland soil than in those incubated in/on abandoned arable soil, indicating that soil origin is also an important factor determining initial wood decay.     

Fungal resistance of rubber wood modified by fatty acid chlorides

Decay resistance of Rubber wood (Hevea brasiliensis) esterified with three fatty acid chlorides (hexanoyl chloride (C6), decanoyl chloride (C10) and tetra-decanoyl chloride (C14)) was evaluated. Unmodified and modified wood samples were exposed to a brown rot (Polyporus meliae) and a white rot (Coriolus versicolor) fungus for 12 weeks. Unmodified rubber wood was severely decayed by P. meliae and C. versicolor, which was indicated by significant weight loss. The rate of decay by brown rot was higher than white rot. Modified wood samples exhibited very good resistant to brown and white-rot fungi. The degree of protection increased with increase in degree of modification. P. meliae, a brown rot fungus, removed structural carbohydrate component in unmodified wood selectively whereas, C. vesicolor showed preference to lignin. The FTIR spectra of modified wood exposed to fungi show no significant changes in relative peak intensities of lignin/carbohydrates indicating effectiveness of chemically modified wood in restricting chemical degradation. Chemical modification occurred more efficiently at carbohydrate portion of the wood. Therefore, it is more effective in retarding decay due to P. meliae.     

Evaluation of Gliocladium roseum Against Wood-Degrading Fungi in vitro and on Major Canadian Wood Species

The protection of wood from fungal stain using biological agents has considerable potential for reducing discoloration of freshly sawn logs and lumber, while decreasing fungicide use. A number of biocontrol candidates have been reported worldwide, and Gliocladium roseum is one of such microorganisms. In this study, the bio-activity of G. roseum was investigated against different wood-degrading fungi on agar plates and wafers of 12 major Canadian wood species. Of the four sap-staining fungi tested on agar plates, Ophiostoma piceae and Alternaria alternata showed greater sensitivity than Aureobasidium pullulans or Cladosporium sphaerospermum to G. roseum . On wood wafers, a spore suspension of G. roseum (1 10 6 spores/ ml) provided satisfactory protection of wood from stain on western hemlock ( Tsuga heterophylla ), white spruce ( Picea glauca ), amabilis fir ( Abies amabilis ), balsam fir ( Abies balsamea ) and jack pine ( Pinus banksiana ). The antagonist also restricted the development of moulds and stain on black spruce ( Picea mariana ), lodgepole pine ( Pinus contorta ) and white pine ( Pinus strobus ), but did not protect Douglas fir ( Pseudotsuga menziesii ), red pine ( Pinus resinosa ), white birch ( Betula papyrifera ) and trembling aspen ( Populus tremuloides ). Logs of black spruce and jack pine treated with G. roseum were much less stained than untreated ones after a 4-month period of summer storage in the field. In an anti-decay test, no significant difference was found for weight loss between wood blocks treated with G. roseum and untreated samples. Application of G. roseum with low levels of an anti-sap stain chemical (NP-1) to wood wafers simultaneously did not produce a noticeable improvement in wood protection against stain compared with the chemical treatment alone.     

Wood decay under the microscope

Many aspects of the interactions between host wood structure and fungal activity can be revealed by high resolution light microscopy, and this technique has provided much of the information discussed here. A wide range of different types of decay can result from permutations of host species, fungal species and conditions within wood. Within this spectrum, three main types are commonly recognised: brown rot, white rot and soft rot. The present review explores parts of the range of variation that each of these encompasses and emphasizes that degradation modes appear to reflect a co-evolutionary adaptation of decay fungi to different wood species or the lignin composition within more primitive and advanced wood cell types. One objective of this review is to provide evidence that the terms brown rot, white rot and soft rot may not be obsolete, but rigid definitions for fungi that are placed into these categories may be less appropriate than thought previously. Detailed knowledge of decomposition processes does not only aid prognosis of decay development in living trees for hazard assessment but also allows the identification of wood decay fungi that can be used for biotechnology processes in the wood industry. In contrast to bacteria or commercial enzymes, hyphae can completely ramify through solid wood. In this review evidence is provided that wood decay fungi can effectively induce permeability changes in gymnospermous heartwood or can be applied to facilitate the identification of tree rings in diffuse porous wood of angiosperms. The specificity of their enzymes and the mild conditions under which degradation proceeds is partly detrimental for trees, but also make wood decay fungi potentially efficient biotechnological tools.     

Resistance of Scots pine wood to Brown-rot fungi after long-term forest fertilization

The susceptibility of Scots pine (Pinus sylvestris L.) sap- and heartwood against the wood decaying brown-rot fungus (Coniophora puteana) was investigated after long-term forest fertilization at three different sites in central Finland. Different wood properties: wood extractives, wood chemistry, and wood anatomy were used to explain sap- and heartwood decay. Scots pine sapwood was more susceptible to decay than its heartwood. In one site, sapwood seemed to be more resistant to wood decay after forest fertilization whereas the susceptibility of heartwood increased. Significant changes in the sapwood chemistry were found between treatment and sites, however, no relationship between wood chemistry and wood decay was observed in the factor analysis. The results of this study show that there was an inconsistent relationship between decay susceptibility and fertilization and the measured physical and chemical attributes of the wood were not consistently correlated with the decay rate.     

Assessing the relative bioavailability of copper to fungi degrading treated wood

Copper is ubiquitous as a biocide component in wood preservatives. Some fungi detoxify copper by immobilizing copper ions with oxalate, decreasing its physiological availability (bioavailability). Decreases in copper bioavailability may also occur during wood treatment. To date, however, copper retention in wood has been measured as overall weight-to-volume concentration without an estimate of its bioavailability and without assessment of its relative contribution to preservative efficacy. Here, we gauge the bioavailability of copper ions in treated wood by using oxalate to pre-treat wood prior to colonization by a moderately copper-tolerant fungus. Copper-treated wood was treated with a gradient of sodium oxalate concentrations, rinsed thoroughly, and exposed in soil-block jars to an isolate of Serpula himantioides. Wood treated with copper ethanolamine was extremely effective in preventing decay by S. himantioides, but toxicity could repeatedly be overcome above a threshold level of oxalate pretreatment. In agar plates, copper-treated wood stimulated oxalate production by S. himantioides, but levels were less than those needed (>10 mM) to overcome copper in soil-block jars. This capacity to overcome copper using an oxalate pretreatment was absent in commercially available samples treated with co-biocide(s). Results demonstrate a useful relative measure of copper bioavailability, with potential to be modified for specific quantification.     

Decay resistance of ash,beech and maple wood modified with N-methylol melamine and a metal complex dye

This study evaluated the decay resistance of ash (Fraxinus excelsior L.), beech (Fagus sylvatica L.), and maple (Acer platanoides L.) wood impregnated by a full cell process with N-methylol melamine (NMM) and combined NMM-metal complex dye (NMM-BS) in aqueous solutions. Basidiomycete decay testing involved incubation with Coniophora puteana (brown rot) and Trametes versicolor (white rot) according to a modified EN 113 (1996) standard, while for the soft rot fungal resistance was evaluated following the standard ENv 807 (2001). NMM and NMM-BS modifications at a WPG range of 7–11% provided decay protection against brown rot resulting in a mass loss less than the required limit (3%). The NMM and NMM-BS modified wood showed increased resistance to white rot decay; however, a higher WPG is needed to prohibit attack from this hardwood specific fungus. The metal-complex dye alone revealed biocidal effects against basidiomycetes. An increased WPG in NMM or NMM-BS had a positive impact against soft rot decay and the lowest mass losses after 32 weeks of exposure were obtained with NMM modification at about 18–21% WPG. NMM modification at this WPG range, however, was not sufficient to protect the wood from soft rot decay. The wood of beech and maple showed slightly higher resistance to all decay types than ash, probably due to the poorer degree of modification of the latter.     

Synergistic effects of cinnamaldehyde in combination with eugenol against wood decay fungi

The combined effects of using cinnamaldehyde with catechin, quercetin or eugenol against wood decay fungi were examined by comparing their isoeffective concentrations to that of individual compound. Among all combinations, cinnamaldehyde with eugenol revealed the strongest synergy against Laetiporus sulphureus. The synergism was due to the interference of fungal cell wall synthesis and cell wall destruction plus radical scavenging effect. Results also suggested that antioxidant with fungicidal effect might be a better candidate than pure antioxidant for the system of fungicide/antioxidant.     

Carbon and nitrogen acquisition strategies by wood decay fungi influence their isotopic signatures in Picea abies forests

We examined whether sporocarp carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N values) reflected different functional strategies in 15 species of wood decay fungi. In Finnish Picea abies forests, we compared sporocarp δ¹³C and δ¹⁵N against log diameter, proximity to ground, and three wood decay types, specifically brown rot, nonselective white rot, and selective white rot (targeting hemicellulose and lignin preferentially). In regression analysis (adjusted r² = 0.576), species accounted for 31% of variability in δ¹³C, with factors influencing wood δ¹³C accounting for the remainder. Brown rot fungi and three white rot fungi that selectively attacked hemicellulose (Heterobasidion parviporum, Phellopilus nigrolimitatus, and Trichaptum abietinum) were higher in δ¹³C than nonselective white rot fungi. This was attributed to greater assimilation of ¹³C-enriched pentoses from hemicellulose by these fungi. The pathogenic white rot fungus Heterobasidion parviporum had higher δ¹⁵N with proximity to ground and increasing log diameter. This suggested that ¹⁵N-enriched soil N contributed to decomposing logs and that Heterobasidion growing from a bigger resource base had increased access to soil N. These isotopic patterns accordingly reflected both functional diversity of wood decay fungi and site-specific factors.