Structural damages to oak wood provoked by some stereales - basidiomycetes decaying fungi

Abstract

The impact of the four Stereales fungi on the anatomical elements of sessile and pedunculate oak has been investigated as follows: Stereum hirsutum, Chondrostereum purpureum and Stereum rugosum known as oak sapwood white rot causers, as well as Xylobolus frustulatus as oak heartwood white - pocket rot (Partridge wood) causer. Samples of sessile- and pedunculate oak sapwood as well as heartwood were exposed to developed dicariotic mycelia of the tested fungi under controlled conditions for 8 weeks. After that period, micro preparations were made for the analysis using light microscope providing normal-, UV-, blue fluorescence- and polarising light, as well as using SEM (Scanning electron microscope). All the tested fungi caused greater damages to the anatomical elements of sessile oak in comparison with pedunculate one. In both cases, the sapwood zone was more damaged than heartwood one. The notified damages of the heartwood, except those for the fungus Xylobolus frustulatus have not been obtained so far. The most affected elements of the both oak species were the fibres of tension wood (G-layers) and parenchyma cells, while tracheas and normal wood fibres, especially in the heartwood zone, were far more resistant to the hyphens of Stereales fungi. In all the tested combinations where damages were notified, fungi had previously consumed the content of the parenchyma cells and have than destroyed the cell-walls of the tension wood fibres, parenchyma cells, and tracheal walls near by pit zones. However, the normal wood fibres, especially in the heartwood zone, were the least damaged or undamaged. During the wall thinning, the damaging advanced from cell lumen to middle lamella. Hyphens were, however, not noted in the intercellular spaces, excepting the final stages of wood cells damaging. Considering the irregular and disordered distribution and appearance of damaged zones inside the wood, the conclusions relating to endangered species or wood zones, need not be considered in the quantitative, but exclusively in qualitative sense.