Resistance of fibre regions in wood of Acer pseudoplatanus degraded by Armillaria mellea

The white rotting Armillaria mellea induced a spatially very distinctive pattern of degradation in sycamore wood, under both natural and artificial conditions. Degradation began preferentially within groups of fibres containing intercellular spaces, whereas fibre regions lacking such spaces were undegraded and remained largely intact even when decay had become advanced elsewhere. The two types of fibre region differed not only in the presence of intercellular spaces, and hence in the potential for gas exchange, but also in their degree of lignification. This was higher in the more resistant type, as shown by staining of undecayed wood with toluidine blue-O, by microspectrometry after staining for the Maule colour reaction, and by uv-microscopy. A spatially similar pattern of cellulose degradation was induced by the brown rotting Laetiporus sulphureus, which is known to cause preferential degradation of less strongly lignified cell walls. By contrast, the white-rotting Ganoderma pfeifferi showed a tendency to degrade the stronger lignified cell walls. Thus, in combination with the application of conventional histological methods, the wood degradation modes observed give additional evidence for stronger and weaker lignified fibre regions within the wood of sycamore.