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Lignin Distribution in Cell Walls of Birch Wood Decayed by White Rot Basidiomycetes. R. A. Blanchette, Associate professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; L. Otjen, and M. C. Carlson. Research fellow, and Junior scientist, respectively, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 77:684-690. Accepted for publication 6 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-684.

Sound wood and wood decayed by various white rot fungi were brominated and analyzed by Energy Dispersive X-ray Analysis (EDXA-STEM) to determine lignin distribution within the cell wall. Lignin was distributed throughout the cell wall in sound wood with the highest concentration in the middle lamella and in cell corners. Wood decayed by Coriolus versicolor, a simultaneous white-rotter, had eroded cell walls with all cell wall components degraded. Lignin was removed from the secondary wall beneath hyphae and around the circumference of the lumen before cellulose loss was detected. Erosion troughs and thinning of the cell walls were evident. Wood decayed by white-rotters that selectively delignified wood, Dichomitus squalens, Heterobasidion annosum, Phellinus pini, Phlebia tremellosus, and Poria medulla-panis, had extensive amounts of lignin removed from throughout the cell wall layers. Lignin was removed in the secondary wall from the lumen toward the middle lamella. The middle lamella between cells was degraded only after extensive lignin depletion in the secondary wall. In advanced stages of decay, lignin was removed from throughout the cell wall layers but not from the cell corners. After delignification, only D. squalens and H. annosum had noticeable amounts of cellulose removed from the secondary wall. Wood fixed with KMnO4 and chemical analyses of lignin and wood carbohydrates confirmed these patterns of lignin degradation from the cell walls.