Dual modes of degradation by Fistulina hepatica in xylem cell walls of Quercus robur

Sequential effects of colonisation by the wood decaying Fistulina hepatica were examined microscopically in naturally infected and artificially inocul ated heartwood of pedunculate oak (Quercus robur). For 6 mo, the deposition of brown materials within parenchyma cells containing hyphae was the only visible effect of colonisation. After 12 mo degradation occurred but was in itially confined to parenchyma of xylem rays, in which the secondary cell w alls showed helically orientated internal cavities containing hyphae, as in a soft rot. The hyphae were covered with a resinous material and persisted in a herring bone pattern after the secondary walls became heavily degrade d. The adjacent libriform wood fibres also showed cavity formation. By cont rast fibre-tracheids were mainly affected by a brown rot. uv-microscopy ind icated that cell types in which the soft rot mode occurred were rich in syr ingyl lignin, whereas the brown rot was associated with cells rich in guaia cyl lignin. Thus, the present study shows that F. hepatica possesses dual m odes of degradation which appear to correlate with the different lignin com position within cell types of oak.