The fungus colonizes wood at an optimum moisture content of 40–100%
(similar to conditions fav orable for brown rot) and progressively erodes
the woody cell wall. All cell-wall layers are eroded in the vicinity of the
hyphae located in cell lumina (Fig. 4a). More advanced stages of decay
showcompletely degraded cell walls adjacent to cells that are not exten-
sively decayed (Fig. 4b, c). This localized degradation of some cells results
in relatively small reductions in wood strength properties until moderate
to advanced stages of decay occur. Some species of white-rot fungi have
the capacity to remove lignin selectively from wood. The removal of lignin
in the cell walls and middle lamella causes cells to detach and separate
from one another (Fig. 4d). The remaining cells consist primarily of cellu-
lose (Blanchette 1990).Mold and stain fungi
Many opportunistic nonwood-destroying fungi colonize freshly cut wood
by utilizing simple sugars and other readily available substances. Surface
molds may discolor the wood with aggregates of pigmented hyphae and
spores or extracellular fungal compounds that stain the wood cell walls
(Table 1). Fungi commonly referred to as stain fungi may penetrate
deepinto the sapwood, preferentially colonizing ray parenchyma cells60 Blanchette
cda bFigure 3a–d
Decay by soft-rot fungi of pine (Pinus) from
Tumulus MM, Gordion, Turkey (700 B.C.E.):
(a) and (b) Transverse sections showing
numerous cavities, characteristic of soft-rot
attack, within the secondary walls of tra-
cheids; (c) and (d) radial sections of tracheids
exhibiting chains of cavities with conical ends
formed within the cell walls. These cavities
are not visible from the cell lumina until the
very advanced stages of decay. Scanning elec-
tron micrographs; bar 5 30 μm.