Mechanisms of reaction zone penetration by decay fungi in wood of beech (Fagus sylvatica)

Fungal growth within reaction zones of beech (Fagus sylvatica) challenged b y three basidiomycetes, Inonotus hispidus, Ganoderma adspersum, Fomitopsis pinicola, and one ascomycete, Ustulina deusta, was studied in naturally col onized and artificially inoculated wood. All the fungi, except F. pinicola, breached reaction zones, but the mechanisms involved were all somewhat dif ferent. Both I. hispidus and U. deusta bypassed blocked cell lumina by tunn elling through cell walls (soft-rot mode), but the latter caused far more d ecomposition of cell walls. Degradation of polyphenols was slight with I. h ispidus and absent with U. deusta. By contrast, G. adspersum preferentially degraded the polyphenolic occlusions in the cell lumina. The failure of F. pinicola to invade reaction zones was typical of a brown rot fungus having limited enzymatic potential and a uniform growth pattern. Mechanisms of le sion expansion, illustrated and summarized in schematic diagrams, are consi stent with earlier observations that reaction zones in beech sapwood are st atic boundaries, which may be successfully breached by white and soft-rot f ungi.