Pitted sap rot
- French disease name: Carie blanche de l'aubier
- Other disease names: Pitted sap-rot
- Pathogen name: Trichaptum abietinum (Dicks.) Ryvarden (Common names for this fungus: purple conk fungus, purple-toothed polypore)
- Kingdom: Fungi
- Phylum: Basidiomycota
- Class: Agaricomycetes
- Order: Hymenochaetales
- Family: Hymenochaetaceae
-
Partial list of synonyms:
- Hirschioporus abietinus (Pers. ex J.F. Gmel.) Donk
- Polyporus abietinus (Pers. ex J.F. Gmel.) Fr.
General information and importance
Trichaptum abietinum is a small, annual, sapwood-decaying basidiomycete with a purple pore surface. It causes a distinctive pitted sap rot in many coniferous species throughout Canada. It is especially common in areas where large numbers of trees have been killed by events such as insect infestation, fire, or windthrow. It is a pioneer decay fungus of dead conifers.
Distribution and hosts
Trichaptum abietinum is endemic to Canada, where it is found in every forested province and territory. It is common on a wide variety of conifer species throughout North America, Europe, and Asia.
Spruce (Picea) and true fir (Abies) species are the most reported hosts because of the large number of dead trees after bark beetle and defoliator outbreaks. Specific conifer species susceptible to pitted sap rot after death include: balsam fir (Abies balsamea), grand fir (A. grandis), subalpine fir (A. lasiocarpa), tamarack (Larix laricina), western larch (L. occidentalis), Englemann spruce (Picea englemannii), white spruce (P. glauca), black spruce (P. mariana), red spruce (P. rubens), Sitka spruce (P. sitchensis), whitebark pine (Pinus albicaulis), jack pine (P. banksiana), shore pine (P. contorta var. contorta), lodgepole pine (P. contorta var. latifolia), western white pine (P. monticola), ponderosa pine (P. ponderosa), red pine (P. resinosa), eastern white pine (P. strobus), Douglas-fir (Pseudotsuga menziesii), eastern white-cedar (Thuja occidentalis), western redcedar (T. plicata ), eastern hemlock (Tsuga canadensis), and western hemlock (T. heterophylla).
There are also occasional reports of non-conifer hosts, including arbutus (Arbutus menziesii), white birch (Betula papyrifera), trembling aspen (Populus tremuloides), and plums and cherries (Prunus spp.). Other Trichaptum species are specific to hardwoods and are more likely to occur on the latter host genera than T. abietinum.
Tree parts affected
The fruiting bodies are produced on dead standing trunks or recently dead fallen conifer logs and branches. It rarely occurs on living trees, except where large wounds have exposed the sapwood. The fungus exclusively colonizes the sapwood of recently dead trees.
Symptoms and signs
The thin, annual fruiting bodies of Trichaptum abietinum are produced in abundance on dead conifers and conifer debris on the forest floor. They emerge from bark crevices on logs and branches. When they develop on the cut end of logs, they cluster in a ring and cover the surface of the exposed sapwood. They are small but often coalesce into large patches. Some lay flat on the bark surface, but most are reflexed to produce a small shelf-like cap (pileus) up to 4 centimetres wide, by 4 centimetres long, by 0.4 centimetres thick. The surface of the pileus is white to grey but may be discoloured green by algae. The texture is velvety to hairy, lacking distinct concentric zones. The interior of the fruiting body (the context) is composed of an upper soft layer and a lower tough and fibrous layer supporting the hymenial layer. The hymenial layer is formed on tubes that open to angular or convoluted (daedaleoid) pores. Young pores have thick intact edges, which become thin, jagged, and tooth-like over time. The tissue between the pores contains hyphal pegs, which are parallel clusters of hyphae that extend into the pore tissues. The pore surface is initially bright purple, aging to reddish brown. The fruiting body produces two types of hyphae (dimitic): thin hyaline (colourless) generative hyphae 2 to 4 micrometres in diameter and skeletal hyphae that are thick walled and branched at the tips, 2.5 to 5.0 micrometres in diameter, extending into the hymenium. The hymenium lining the pores is composed of a tightly packed palisade of basidia and cystidia. Basidia are cylindrical, 12.5 to 14 micrometres × 5 to 6 micrometres in size, and bear four hyaline, cylindrical, slightly curved basidiospores measuring 6.0 to 7.5 micrometres × 2.5 to 3.0 micrometres. The hyaline cystidia are numerous, club-shaped, and 4 to 7 micrometres in diameter. They arise from the skeletal hyphae, protruding up to 15 micrometres beyond the basidia, and are encrusted with crystals at the apex.
The decay is a white pitted rot of the sapwood. The fungus degrades both cellulose and lignin in the wood. In early stages of decay, the sapwood becomes light yellow to tan in colour and soft. As the decay advances, small, elongated, whitened areas develop parallel to the grain of the wood. These areas soon degrade to create pits, forming a honeycomb pattern in cross section. In late stages of decay, the wood is very fragile and lacy due to the numerous pits.
The closely related species Trichaptum laricinum and T. fuscoviolaceum also occur on conifers. These species, however, produce gill-like plates on the undersurface instead of pores. Trametes versicolor, a common polypore that occurs on conifers, has a similar pileus. It is usually wider, with concentric zones of dark and light colouration. Its pore layer is tan to white in colour (never purple). Stereum sanguinolentum also has a similar pileus, but its undersurface, which has no pores, stains red when fresh.
Disease cycle
New fruiting bodies are produced annually, developing after the wood has become extensively colonized. Basidiospores are released from the fruiting body pores and become windborne. If they land on exposed sapwood of a dead conifer host, they germinate and begin to form a decay column. Events that kill large numbers of trees, such as windstorms and insect infestations, provide abundant substrate for T. abietinum.
Damage
Sap rots, such as those caused by T. abietinum, reduce the amount and quality of salvageable wood in conifer forests killed by events such as fire, insect infestations, or windstorms. They also can reduce the quality of pulp produced for the manufacture of paper if the areas of advanced decay, which are close to the bark, are not removed during the debarking process.
In western and southern Ontario, sapwood of spruce and balsam fir killed by the spruce budworm (Choristoneura fumiferana) undergoes rapid colonization by a succession of organisms. Trichaptum abietinum is one of the pioneering fungi at the onset of decay. In the first year after the trees are killed, they are primarily colonized by Stereum chailletti, a decay fungus that is transmitted by Sirex wood wasps. A year or more later, advanced pitted sap rot sets in, the majority of which (95%) is caused by T. abietinum. Rapid onset of damage due to pitted sap rot frequently coincides with the presence of high populations of the balsam fir bark beetle (Pityokteines sparsus). Although there is no evidence that the balsam fir bark beetle plays a direct role in establishing T. abietinum colonization, the presence of the beetle indicates the likely presence of pitted sap rot.
In northeastern Ontario, New Brunswick, and Newfoundland, the decay process after tree death is much slower. There are low levels of pitted sap rot in budworm-killed trees until 4 or more years after tree death. A study of wind-thrown balsam fir in Newfoundland found that there was negligible advanced sapwood decay after 4 years. After 8 years, however, 45% of the gross merchantable volume was affected in the 175 trees examined. Trichaptum abietinum was the second most important fungus associated with advanced sapwood decay. Pitted sap rot is also associated with Douglas-fir killed by Douglas-fir beetle (Dendroctonus pseudotsugae) in western North America.
Prevention and management
Dead trees killed by major disturbances should be harvested as soon as possible to prevent or minimize losses due to pitted sap rot. During salvage operations, peeled logs are less likely to develop extensive sapwood decay than those with bark. A large amount of the decayed sapwood is removed during the debarking process because it is soft. Longer logs deteriorate more rapidly in storage than short logs.
Pest management strategies for a particular pest vary depending on several factors. These include:
- the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
- the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
- an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
- how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
- the value of the host(s) versus the costs of pest management approaches; and
- consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.
Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.
Photos
A cross-section of a balsam fir trunk with pitted sap rot caused by Trichaptum abietinum.
Gaston Laflamme
Fruiting bodies of the fungus Trichaptum abietinum on the bark of red spruce.
Claude Moffet
Fruiting bodies of the fungus Trichaptum abietinum on the bark at the base of a red spruce.
André Carpentier
Old fruiting bodies of Trichaptum abietinum with algae growing on the upper surface.
Eric Allen
The ridged pore layer of Trichaptum abietinum fruiting bodies.
Eric Allen
A typical occurrence of multiple fruiting bodies of Trichaptum abietinum on a dead Douglas-fir stem.
Richard Reich
Selected references
Allen, E.A.; Morrison, D.J.; Wallis, G.W. 1996. Common tree diseases of British Columbia. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. 178 p.
Basham, J.T. 1957. The deterioration by fungi of jack, red, and white pine killed by fire in Ontario. Canadian Journal of Botany 35(2): 155–172. https://doi.org/10.1139/b57-016
Gilbertson, R.L.; Ryvarden, L. 1987. North American Polypores Vol. 2.: Megasporoporia – Wrightoporia. Fungiflora, Oslo, Norway. pp. 437–885.
Ginns, J. 2017. Polypores of British Columbia (Fungi: Basidiomycota). Province of British Columbia, Victoria, British Columbia. Technical Report 104. www.for.gov.bc.ca/hfd/pubs/Docs/Tr/TR104.htm [Accessed April 2024]
Ko, K.S.; Hong, S.G.; Jung, H.S. 1997. Phylogenetic analysis of Trichaptum based on nuclear 18S, 5.8S and ITS ribosomal DNA sequences. Mycologia 89(5): 727–734. https://doi.org/10.1080/00275514.1997.12026839
Niemelä, T.; Renvall, P.; Penttilä, R. 1995. Interactions of fungi at late stages of wood decomposition. Annales Botanici Fennici 32(3): 141–152. https://www.jstor.org/stable/23726315
Parry, D.L.; Filip, G.M.; Willits, S.A.; Parks, C.G. 1996. Lumber recovery and deterioration of beetle-killed Douglas-fir and grand fir in the Blue Mountains of eastern Oregon. United States Department of Agriculture, Forest Service, Pacific Northwest Research Station. Portland, Oregon. General Technical Report PNW 376. 24 p.
Stillwell, M.A. 1959. Further studies of the pathological deterioration in wind-thrown balsam fir in Newfoundland. The Forestry Chronicle 35(3): 212–218. https://doi.org/10.5558/tfc35212-3