Fungal Decay of Wood: Soft Rot—Brown Rot—White Rot

Abstract

Wood decay by fungi is typically classified into three types: soft rot, brown rot and white rot. Brown rot fungi are the most prevalent with regard to attack on coniferous, structural wood products in North America. The wood decayed by brown rot fungi is typically brown and crumbly and it is degraded via both non-enzymatic and enzymatic systems. A series of celluloytic enzymes are employed in the degradation process by brown rot fungi, but no lignin degrading enzymes are typically involved. White rot fungi are typically associated with hardwood decay and their wood decay patterns can take on different forms. White rotted wood normally has a bleached appearance and this may either occur uniformly, leaving the wood a spongy or stringy mass, or it may appear as a selective decay or a pocket rot. White rot fungi possess both cellulolytic and lignin degrading enzymes and these fungi therefore have the potential to degrade the entirety of the wood structure under the correct environmental conditions. Soft rot fungi typically attack higher moisture, and lower lignin content wood and can create unique cavities in the wood cell wall. Less is known about the soft rot degradative enzyme systems, but their degradative mechanisms are reviewed along with the degradative enzymatic and non-enzymatic systems known to exist in the brown rot and white rot fungi. As we learn more about the non-enzymatic systems involved in both brown and white rot degradative systems, it changes our perspective on the role of enzymes in the decay process. This in turn is affecting the way we think about controlling decay in wood preservation and wood protection schemes, as well as how we may apply fungal decay mechanisms in bioindustrial processes.