Fungicides for Wood Protection - World Viewpoint and Evaluation/Testing in Slovakia

Abstract

Hardwoods (e.g. ash, beech, oak, poplar) and softwoods (e.g. fir, pine, spruce) consist of various types of cells: vessel elements, tracheids, libriform fibres, axial parenchyma cells, ray parenchyma cells, epithelial cells, etc. These cells exhibit various orientations in relation to the standing tree and provide various functions, such as, imparting mechanical strength, acting as water-conducting elements, or functioning as storage cells. Wood cells, their cell walls and lumens have typical shapes and dimensions. Cell walls usually consist of primary and secondary wall layers which are made up from basic natural polymers: cellulose, hemicelluloses and lignin. Extractives of durable wood species (such as terpenoids, tropolones, stilbenes, flavonoids or chinones) are usually present in the cell lumens, or sometimes even in the cell walls (Fengel & Wegener 1984). Wood is a natural organic material and as such it can be degraded by biological agents: bacteria, fungi and insects. The use of wood is thereby limited by its susceptibility to organisms that may damage its structure and deteriorate its properties. Wood-destroying fungi, such as brown-rot (Serpula lacrymans, Coniophora puteana, Antrodia vaillantii, Gloeophyllum trabeum, Lentinus lepideus, etc.) and white-rot (Trametes versicolor, Trametes hirsuta, Schizophyllum commune, etc.) basidiomycetes, or soft-rot (Chaetomium globosum, Monodictys putredinis, etc.) ascomycetes, destroy polysaccharides (cellulose and hemicelluloses) present in the cell walls. They may also, in different degrees, degrade the lignin (Arantes et al. 2010, Schmidt 2006). Fungi attain the depolymerization of polysaccharides by producing various types of hydrolytic enzymes, e.g. degradation of crystalline cellulose is achieved using etracellular endo-1,4-s-glucanases, exo-1,4-sglucanases, and 1,4-s-glucosidase. Brown rot-fungi which do not have exo-1,4-sglucanases use the low molecular non-enzymatic Fenton chelator-mediated system consisting of oxalic acid, iron cations and hydrogen peroxide (Eriksson et al. 1990, Goodell et al. 2007, Hastrup et al. 2010, Messner et al. 2003). Rotten wood has lower density and lower strength (Reinprecht 1992, Wilcox 1978). In parallel to the changes above, rot-fungi also change the moisture, colour, acoustic and other properties of wood, with an expressive influence on wood quality. However, these fungi can only degrade the structural components of wood in situations when its moisture content (MC) is 20 % or more (Carll & Highley 1999).