Wood discoloration caused by staining fungi and moulds

ABSTRACT • Some moulds also cause wood discoloration in later stages of their growth but mostly on the surface. The most notable wood discolouring moulds genera are Aspergillus, Penicillium and Trichoderma. Some Trichoderma species cause increasing of permeability of infected wood. Staining fungi are divided into two groups: sapstain - discoloration of logs and fresh cut boards, and bluestain - discoloration of wood in use. The most important sapstaining fungi are of the following genera: Ceratocystis, Ceratocystiopsis, Ophiostoma, Sphaeropsis and Lasiodiplodia. They are dispersed by wind and rainfall water but also by insects (active - insects wear spores on or in their body, and passive - spores are introduced into insect holes by wind or water). In live trees these fungi are also strong pathogens. Important bluestaining fungi are the following genera: Cladosporium, Aureobasidium, Alternaria and Phialophora. Species of genera such as Ceratocystis, Aureobasidium, Alternaria and Phialophora cause the increase of permeability, decrease of density and consequently the decrease of some mechanical properties. Some species of genus Aureobasidium are common in woodin-service, where they break out coatings and colour wood into black. They are mostly dispersed by wind and rainfall water. Wood discoloration is a process caused by staining fungi and hence it is not only harmful for the surface but also for the entire wood. Depending on staining fungi species and wax stages, wood could be slightly damaged, and the use of such wood is restricted. Such wood discoloration should be seriously considered, and the possibility of infection by staining fungi reduced in all stages of wood processing. An environmentally friendly way of reducing infection and quantity of wood discoloration is to make unfavourable conditions for fungal growth by keeping moisture content over or under favourable values or by removing carbohydrates, starch, fats and proteins out of the wood.