Fornes annosus - A forest pathogen.

Abstract

Fornes annosus (Fries) Cooke is a pathogenic fungus that decays roots and heartwood of living trees. The fungus is one of the most destructive of all the parasites encountered in coniferous plantations. Its distribution is widespread. Modern silvicultural practices have enhanced its spread and development. The pathogen has a life cycle typical of most wood-inhabiting Hymenomycetes. Inoculation occurs when basidiospores of the fungus come in contact with freshly cut stump surfaces or other wounds. If environmental conditions are favourable, such as temperature and relative humidity, germination penetration and colonisation occurs and eventually the sexual stage, a perennial basidiocarp, develops on the stump or root surface. Basidiospores released from these fructifications are disseminated by wind and are eventually deposited by impaction or gravity. The disease cycle may be renewed by viable spores which alight on a suitable substrate, such as an exposed stump. Secondary disease cycles have not been studied in great detail but it has been shown that the conidial state, Oedocephalum lineatum Bakshi, is also capable of stump infection. Disease losses occur as the fungus grows, via root contacts from colonised stumps to living trees, where it causes a root and butt decay. The merchantable volume of timber, therefore, is greatly reduced and the infected trees are liable to be wind-blown. An intensive research programme has been initiated to study the complexity and diversity of this ubiquitious pathogen. Chemical treatment of stumps has been the chief method of control used although biological control by stump inoculation with antagonistic microorganisms has also been suggested. However, as with many diseases of forest trees, there is need for an economically feasible silvicultural control.