Cavity Formation and the Exposure of Peculiar Structures in the Secondary Wall (S2) of Tracheids and Fibres by Wood Degrading Basidiomycetes

Abstract

The formation of cavities in the secondary wall (S 2 ) of fibres and tracheids was revealed in wood artificially incubated and naturally infected by a range of wood degrading basidiomycetes. Cavity formation is a characteristic feature of soft rot attack. the observed phenomena however differed from a soft rot mode of attack as hyphal growth was not ascertained within the cell walls. Atypical for a soft rot. or any commonly described white rot degradation pattern, extensive delignification always preceded cavity formation. Single cavities were separated from another within the secondary wall (S 2 ) by peculiar conspicuous radial structures, which apparently have not been described in white-rotted wood before. Radial structures were orientated perpendicular to the middle lamella and extended from the S 1 to the S 3 . Like the S 3 , the exposed radial structures, which revealed birefringence when viewed between crossed nicols, showed an inherent resistance to degradation by the selected basidiomycetes. The presence of cellulose within radial structures of the delignified secondary walls (S 2 ) was also confirmed by staining techniques.