DEVELOPMENT AND PROGNOSIS OF DECAY IN THE SAPWOOD OF LIVING TREES

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Abstract
Fungal growth within reaction zones of London plane (Platanus x hispanico Muenchh.), beech (Fagus sylvatica L.) and large-leaved lime (Tilia platyphyllos Scop.) infected with three basidiomycetes Inonotus hispidus (Bull.:Fr.) Karst., Ganoderma adspersum (Schulz.) Donk, Fomitopsis pinicola (Fr.) Karst, and one ascomycete Ustulina deusta (Fr.) Petrak, was studied in naturally colonised and artificially inoculated wood. With the exception of F. pinicola all the other decay fungi successfully defeated reaction zones. The mechanisms, however, of reaction zone penetration by these species were all somewhat different in nature. Inonotus hispidus defeated reaction zones via soft rot, bypassing blocked cell lumina without causing substantial decomposition of cell walls and polyphenols. Invasion of reaction zones by Ganoderma adspersum was characterised by the preferential degradation of polyphenols. In contrast, Ustulina deusta failed to defeat reaction zones in beech, but readily penetrated reaction zones in large-leaved lime. Failure of Fomitopsis pinicola to invade and defeat reaction zones in beech is apparently related to the limited enzymatic ability and inflexible behaviour of brown rot fungi. Mechanisms of lesion expansion are illustrated and summarised in schematic diagrams. They support former observations that decay fungi may successfully defeat reaction zones.