| Themes > Science > Botanical Sciences > Trees Pathology > Wood Decay | ||||||||||||||||||||
Wood decay is a deterioration of wood by primarily enzymatic activities of microorganisms. For practical purposes, fungi are the only agents of wood decay. There are other kinds of deterioration, by insects, marine animals, UV, but this is not decay, nor is it quantitatively as important as decay.
White rotWhite rot is fibrous because some cellulose remains intact till very late stages. It usually turns whitish because of bleaching by oxidation and loss of lignin, which is slightly brown. Color and texture vary among white rots caused by different fungi:
In some white rots, there is a phenomenon called selective delignification. All components are removed, but the relative rate varies. Lignin and hemicelluloses are selectively removed in early stages. This leaves enriched cellulose. This is what happens in the white regions of a mottled rot and in the pockets of a white pocket rot. There is a tremendous amount of interest in using these fungi in industry, because many uses of wood involve removing lignin (e.g., biopulping). EthnopathologyIn Chile, selectively delignified wood of the genus Nothofagus occurs in large amounts. It is mostly associated with decay by Ganoderma species and is called palo podrido. Dr. Robert Blanchette reports that Indians in Chile have (had) a god called Trauco. Trauco lives in the forest and looks like a man but has cloven feet. Trauco represents fertility, perhaps in much the same way as of the Indians of southwestern North America. Unwed women who got pregnant often said that Trauco had visited them and he was responsible for their pregnancy. Trauco eats palo podrido, and there are reports that Indians did as well, perhaps to enhance fertility. In selectively delignified wood there are often pockets of clear, gelatinous remnants of the wood. Armillaria species in particular often cause these gelatinous pockets. This may become colonized by yeast and may contain alcohol. We don't know what role this may play in the legend, but one noted forest pathologist who was trying to have kids ate some Armillaria jelly while on a trip and his wife became pregnant soon after! Incidentally, the delignified wood is quite useful as fodder for ungulates. It can be readily broken down with the aid of microorganisms in their gut. Even in Alaska, I have seen evidence that moose have fed on logs decayed by Ganoderma applanatum! Brown RotBrown rot is brown because carbohydrates are removed, leaving brownish, oxidized lignin. There is no fibrous texture because the cellulose is broken up early. The wood shrinks on drying and cross-checking is seen in later stages. Often called "cubical" brown rot for that reason. There are a handful of "brown pocket rots." They only occur in living trees. The initial stage is non-enzymatic. Fungus produces some small chemical agent that zips around in the cell wall like a little pair of scissor, snipping chains of cellulose and hemicellulose into smaller pieces. This happens throughout the wall in fairly early stages. The carbohydrates become partly soluble, enzymes work on them, releasing sugars, and they are slowly absorbed by the fungus. Soft RotThe best known feature is the curious cavities in the secondary wall. They are not always present. |
||||||||||||||||||||
|
|