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Cytology and Histology

Selective Delignification of Eastern Hemlock by Ganoderma tsugae. Robert A. Blanchette, Assistant professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; Phytopathology 74:153-160. Accepted for publication 14 June 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-153.

Ganoderma tsugae caused two distinct types of degradation in naturally decayed eastern hemlock, Tsuga canadensis. Large areas of wood were selectively delignified and a white rot, characterized by simultaneous removal of lignin and carbohydrates from the cell walls, occurred in localized areas. Scanning and transmission electron micrographs of delignified wood demonstrated a diffusible ligninolytic system that caused degradation of the compound middle lamella without substantial alteration of the secondary wall. The S₂ layer of the secondary wall remained least affected. Chemical analyses of delignified wood indicated hemicelluloses were removed in preference to cellulose when lignin was degraded. Pseudosclerotia, or zone lines, present in the outer edges of decayed logs and stumps were morphologically different from the black areas that occurred only in delignified wood. Micromorphological and ultrastructural studies made possible a schematic illustration of decay patterns caused by G. tsugae in eastern hemlock wood.