Blue stain (synonymous sap stain) is a blue,grey or black, radially striped dially stri wood discoloration of sapwood, which can be caused by about 100 to 250 (Kaarik 1980) fungi belonging to the Ascomycetes and De (1999) and others differentiated three uteromycetes.
Seifert groups of blue-stain fungi: - Cerato-cystis, Ophiostoma and Ceratocystiopsis species (Upadhyay 1981; Perry 1991; Gibbs 1999), - black yeasts such as Hormonema dematioides, Aureobasidium pullulans, Rhinocladiella atrovirens, and Phialophora species, - dark molds such as Alternaria alternata, Cladosporium sphaerospermum, and C. cladospo-rioides. Yang (1999) differentiated dark staining fungi, such as Ophiostoma piliferum on jack pine, Ceratocystis minor on white pine, and C. coerulescens on white spruce, and light staining fungi, such as 0. piceae, C. adiposa and Leptographium sp.
Frequently, like in the Ophiostoma species, the teleomorph is a perithecium . Blue stain occurs in conifers, particularly in pine, but also in spruce, fir, and larch, in hardwoods, like beech and birch, and in tropical woods. The stain may be superficial or penetrate deeply into the wood. In heartwood species, only the sapwood discolors, since blue-stain fungi live mainly on the content of the parenchyma cells. shows some details of blue stain.
The hyphae are brown colored due to melanin (Zink and Fengel 1989) and relatively thick . Some species like A. pullulans develop dark-brown, thick-walled chlamydospores .
The blue-black color of th. e wood develops as optical effect due to refraction of light. Hyphae penetrate into stem wood from cross sections or radially through bark fissures and move via the medullary rays. Easily accessible nutrients (sugars, carbohydrates, starch, pro-teins, fats, extractives) are taken up lase have from the ray parench.)rmacells.bXluylea-nstaasien nnanase, p Xylanase, maectinase and amye been detected in several fungi s of the bordered through the torus (Schirp et al. 2003a).
From the rays, the hyphae penetrate into the longi-tudinal tracheids with mechanical pressure pits (thin hyphae through the margo) and grow there from cell to cell through the pits. Because fungi colonize the sapwood tracheids and fibers, components of the capillary liquid also might be used as nutrients. Although there are special microhyphae, transpressoria , which can break through the wood cell wall, probably by physical pressure and/or enzymatic action (Schmid and Liese 1966; Liese 1970), in most cases the strength properties of wood are hardly affected. Thus, the occasionally used term "blue rot" is wrong. Some species however caused some strength loss. Toughness was the property most seriously affected (Seifert 1999; Schirp et al. 2003b). In most cases, however, the damage to wood is mainly cosmetic.
The damage however affects domestic and export earnings for the forest industries. For example, Pinus radiata in New Zealand is highly susceptible to blue stain with an estimated annual loss in revenue of NZ$ 100 million per year (Thwaites et al. 2004). Temperature minimum depends on the species, and is between 0 and —3°C; the optimum is between 18 and 29 °C and the maximum is between 28 and 40 °C. The moistures pan reaches from fiber saturation close to umax. In many species, the optimum is between 30 and 120%(Kaarik 1980; Schumacher and Schulz 1992). For log colonization, moisture loss in the felled tree of 10-15% is sufficient.
Blue stain occurs during seasoning or transportation ofgreen lumber before the wood is dried and is enhanced at relative humidities above 90% (Seifert 1999). Blue-stain fungi were arranged into different ecological groups (Butin 1995): In blue stain of stems (primary blue stain), spores of Ophiostoma species (mois-ture optimum 50-130%), particularly Ophiostoma piceae (Harrington et al. 2001) and also Discula pinicola are transferred by wind in bark wounds (forest work or wood transport) as well as by bark beetles particularly in un-debarked pine stems which are allowed to dry out slowly over weeks or months while ly-ing in the forest (Neumaller and Brandstatter 1995).
Hormonema dematioides, A. pullulans, and a Leptographium species were the most frequently isolated stain-fungi from bark and sapwood of living Pinus banksiana trees. There were indications that none of the well-known log-staining fungi was associated with healthy living jack pine trees, and it was deduced that prompt transportation of logs from forests to sawmills and sanitary treatment of log storage yards thp ceverity- of log staining before sawing (Yang 2004)