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Stringy Butt Rot

Perenniporia subacida (Peck) Donk
(= Poria subacida (Peck) Sacc.)

Basidiomycotina, Aphyllophorales, Polyporaceae

Hosts: Perenniporia subacida is found in a wide range of coniferous and deciduous hosts. In B.C., it has been reported on amabilis, grand, and subalpine fir, tamarack, Engelmann, white, and Sitka spruce, lodgepole, Scots, and western white pine, Douglas-fir, western redcedar, western hemlock, maple, alder, arbutus, birch, cherry, cottonwood, and willow. Elsewhere in North America it has also been found on mountain hemlock, western larch, juniper, chestnut, tulip-tree, and cypress.

Distribution: This fungus is widely distributed throughout the range of its hosts in B.C.

Identification: The fruiting bodies are perennial, resupinate, and leathery to crust-like (Fig. 17a). The exposed surface is cream to light yellow and poroid; the pores are circular in outline, 5-6 per mm. Fruiting bodies may form on living trees, especially western redcedar, but are generally found on the underside of decayed logs or on the lower stem of dead-standing trees.

The early stage of decay appears as a light brown stain. Later, small white pits develop and coalesce to form a mass of white spongy fibres containing small, black flecks (Fig. 17b). Annual rings may separate to form a laminate decay; yellow-white mycelial mats frequently form between the sheets. The yellow colour of mycelial mats is relatively unique to this fungus. In the final stage, the wood is completely destroyed, leaving a hollow butt (Fig. 17c).

Microscopic Characteristics: Hyphae in the context of the fruiting body thin-walled with clamp connections. Basidiospores ovoid to broadly ellipsoid, hyaline, thin-walled, smooth, IKI-, 4.5-7.5 x 3-5 µm. Growth in culture moderately rapid, mat white, laccase positive, fibre hyphae common. Stalpers: 1 3 (6) (7) (11) (13) (14) 17 19 21 22 24 25 30 37 39 42 44 45 46 (47) 50 51 52 53 54 78 (80) 83 (88) (89) 90.

Damage: The presence of fruiting bodies on living trees indicates up to 3-4 m of defect; on dead trees fruiting bodies indicate almost total cull.

Remarks: Root and butt decay caused by P. subacida can cause significant losses and predispose infected trees to wind throw.


Gilbertson, R. L. and L. Ryvarden. 1987. North American Polypores. 2:531. Fungiflora, Oslo.



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P. subacida sporophore on western redcedar - Click on this image to see a larger version

Figure 17a: P. subacida sporophore on western redcedar.




Advanced decay with mycelial mats - Click on this image to see a larger version Figure 17b: Advanced decay with mycelial mats caused by P. subacida.





Advanced decay with mycelial mats - Click on this image to see a larger version Figure 17c: Advanced decay with mycelial mats caused by P. subacida.