Wood decay Fungus
Wood decay Fungus
Brown Rot
Brown-rot fungi break down hemicellulose and cellulose that
form the wood structure. Cellulose is broken down by hydrogen
peroxide (H2O2) that is produced during
the breakdown of hemicellulose. Because
hydrogen peroxide is a small molecule,
it can diffuse rapidly through the wood, leading to a decay that is not
confined to the direct surroundings of the fungal hyphae. As a result of
this type of decay, the wood shrinks, shows a brown discoloration, and cracks
into roughly cubical pieces, a phenomenon termed cubical fracture. The fungi of certain
types remove cellulose compounds from wood and hence the wood becomes
brown colour.
Brown rot in a dry, crumbly condition is sometimes incorrectly
referred to as dry rot in general. The term brown rot replaced
the general use of the term dry rot, as wood must be damp to decay,
although it may become dry later. Dry rot is
a generic name for certain species of brown-rot fungi.
Brown-rot fungi of particular economic importance include Serpula
lacrymans (true dry rot), Fibroporia vaillantii (mine fungus),
and Coniophora puteana (cellar
fungus), which may attack timber in buildings. Other brown-rot fungi include
the sulfur shelf, Phaeolus schweinitzii, and Fomitopsis pinicola.
Brown-rot fungal decay is characterised by extensive
demethylation of lignins whereas white-rot tends to produce low yields of
molecules with demethylated functional groups.
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Soft-rot fungi secrete cellulase from
their hyphae,
an enzyme that
breaks down cellulose in the wood. This leads to the formation
of microscopic cavities inside the wood, and sometimes to a discoloration and
cracking pattern similar to brown rot.[4][5] Soft-rot
fungi need fixed nitrogen in order to synthesize enzymes, which they
obtain either from the wood or from the environment. Examples of
soft-rot-causing fungi are Chaetomium, Ceratocystis,
and Kretzschmaria deusta.
Soft-rot fungi are able to colonise conditions that
are too hot, cold or wet for brown or white-rot to inhabit. They can also
decompose woods with high levels of compounds that are resistant to biological
attack. Bark in woody plants contains a high concentration of tannin,
which is difficult for fungi to decompose, and suberin which
may act as a microbial barrier. The
bark acts as form of protection for the more vulnerable interior of the plant. Soft-rot
fungi do not tend to be able to decompose matter as effectively as white-rot
fungi: they are less aggressive decomposers
White Rot
White-rot fungi break down the lignin in
wood, leaving the lighter-colored cellulose behind; some of them break down
both lignin and cellulose. As a result, the wood changes texture, becoming
moist, soft, spongy, or stringy; its colour becomes white or yellow. Because
white-rot fungi are able to produce enzymes, such as laccase,
needed to break down lignin and other complex organic
molecules, they have been investigated for use in mycoremediation applications.
There are many different enzymes that are involved in the decay
of wood by white-rot fungi, some of which directly oxidize lignin. The
relative abundance of phenylpropane alkyl side chains of
lignin characteristically decreases when decayed by white-rot fungi. It
has been reported that the oyster mushroom (Pleurotus ostreatus)
preferentially decays lignin instead of polysaccharides. This
is different from some other white-rot fungi, e.g., Phanerochaete chrysosporium, which
shows no selectivity to lignocellulose.
Other white-rot fungi include the turkey tail, artist's conk, and tinder fungus.
White-rot fungi are grown all over the world as a
source of food .
Blue stain Fungi
Blue stain fungi (also
known as sap stain fungi) is a vague term
including various fungi that cause dark staining in sapwood. The
staining is most often blue, but could also be grey or black
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