Figure 87

Figure 88

There are, of course, many variations to the five basic themes.

Discolored wood. Color of the wood is changed when cell contents are altered.

Bacter1a anaerobic, aerobic, and facultative forms - and nondecay fungi usually are involved in these processes, but decay fungi can also be involved.

Some genera of fungi commonly associated with discolored wood are:
Ceratocystis, Fusarium, Trichocladium, Hypoxylon, Graphium, Phialophora, Leptographium, Alternaria, Pullularia, Torula, and Rhinocladiella. Also associated are species of Fomes and Polyporus. Plugging in vessels can impart a color change, a vertical type of discoloration, but most color changes result from alteration of cell contents in ray parenchyma (radial discoloration). Some slight discolorations can result from the reaction of the tree alone to a wound, but intense discoloration usually involves the interaction of microorganisms with living and dying cells in the tree.

Blue stain fungi in white pine-tangential section through discolored rays. Bacteria are clustered near pits. (fig. 87)

Blue stain fungi in white pine-radial section through discolored rays. Bacteria are clustered in the ray cells.

Figure 91  Magnified section of above showing vessel plugs.

	Figure 89 Transverse section through discolored wood surrounding decayed wood in Populus tremuloides. (see fig.30)
	Figure 90 Radial section of discolored rays in red maple

	Figure 92 White rot associated with stub in white pine
	Figure 93 Close-up of white rot in pine.

White rot.

The cellulose and lignin are digested at about equal rates. The digestion usually starts from the cell lumens and proceeds towards the middle lamella. Hymenomycetes are involved mostly, although species in the Xylariaceae also are associated with white rot (genera-Hypoxylon Xylaria, Daldinia). There are many types of white rot (fleck, stringy, ring, pocket, etc.). These terms describe their macroscopic appearance. White rots occur also in wood products such as utility poles. Some of the most damaging fungi associated with white rots are Phellinus pini, Armillariella mellea, Fomitopsis annosa, Ganoderma applanatum, Oxyporus populinus, Phellinus igniarius, Innotus glomeratus, I. obliquus, and Echinodontium tinctorium. (figs. 92-94)

	Figure 95 Brown rot in southern yellow pine
	Figure 95 Closeup of brown rot in pine

Brown rot.

The cellulose is digested preferentially, and the lignin is only altered slightly in this type of rot. Brown rots have a shrunken cubical appearance. Brown rots occurs mostly in gymnosperms and in wood products. Some common fungi associated with brown rots are Phaeolus schweinitzii, Poria monticola, Lentinus lepideus, and Polyporus betulinus. Polyporus sulphureus and Fomes pinicola are examples of fungi that cause the less common brown rot in angiosperms. (figs. 95-96)

Soft rots

The S₂ layer of the middle cell wall is digested by some microorganisms. (fig. 97) Several patterns of digestion occur: Rhomboid cavities, (fig. 98) long spindle- shaped cavities, and a general breakdown of the S₂ layer. Many variations occur. The causal fungi are usually nonhymenomycetes- Phialophora, Penicillium, Chaetomium, etc. Soft rots occur mostly in moisture-saturated angiosperm wood products. Little is known about soft rots in living trees.

Bacterial alteration.

Little is known yet about the effects of bacteria alone on wood. In ponded logs, bacteria do invade pits-mostly the microfibrils of the pit margos. Under some conditions, bacteria have been known to digest some cell wall constituents. Some bacteria genera commonly associated with this type of wood alteration are Pseudomonas, Bacillus, and Clostridium. Bacteria are often intimately associated with fungi in the decay process. Many bacteria are facultative forms. (fig. 99)

Figure 97 Cavities in cells
Figure 98 Rhomboid cavities in walls

Figure 99 Bacteria on pine pits.

Wetwood

Figure 100   Wetwood associated with small stubs in white fir.

Bacteria are the only major organisms associated with a wood condition called wetwood. The infected wood may or may not be darkly discolored. The infected wood may have a bleached or glassy appearance. (figs 100-101)

Figure 101    Wetwood zones in white fir

Slash deterioration

Dead wood on the forest floor is inhabited by a wide variety of microorganisms that continue their activities until the wood is completely decomposed. The microorganisms compete among themselves under constantly changing environmental conditions. (fir. 102)

Table of Contents Previous Section | Next Section