Brown trunk rot

Micro-habitat(s)

Trunk

Distribution

North America

This fungus is widely distributed throughout the range of its hosts in British Columbia.

Damage, symptoms and biology

The early stage of decay appears as a light yellow to red-brown stain or, in the case of Douglas-fir, as a purple discolouration. The stain may extend for a considerable distance beyond the advanced decay. In the late stage the wood breaks into brown cubes and thick (5 mm) white mycelial felts may form in the shrinkage cracks.

The fruiting bodies are perennial and vary from hoof-shaped to long pendulous structures. They vary in size from a few to 40 cm in diameter. The upper surface is zoned, white when fresh but drying to dark grey or light brown in old specimens; a chalky coating, which rubs off as a white powder, may be present. The lower surface is white when fresh, drying to light brown, and is poroid; the pores are relatively small and uniform in outline. The context is white or grey, relatively soft when young, toughening with age, and distinctly bitter in taste.

Other information

Fruiting bodies are formed relatively frequently on larch, and are less common on other species. On all hosts a single fruiting body indicates that most of the wood volume has been destroyed. Trees in recreation areas with conks should be considered highly hazardous and should be removed. The decay caused by F. officinalis can be confused with other brown cubical rots such as Laetiporus sulphureus, Phaeolus schweinitzii, or Fomitopsis pinicola. Fomitopsis officinalis, however, has thicker mycelial mats and is more common higher on the stem. Another distinguishing feature is the bitter taste of the sporophore context and mycelial mats, a characteristic that has given this fungus the common name "quinine fungus."

Microscopic Characteristics:
Hyphae in the context of the fruiting body thin-walled, hyaline, with clamp connections. Basidiospores cylindric-ellipsoid to short-cylindric, hyaline, smooth, IKI-, 6-9 x 3-4 µm. Growth in culture very slow, mat white, laccase negative, chlamydospores common, conidia numerous, borne singly on branches, ovoid, 4.5-7.5 x 3-4.5 µm. Stalpers: (10) (11) (12) 13 14 (15) 17 (18) 21 22 (24) (26) 30 (36) (38) 39 42 45 (51) 52 53 54 (75) (80) 83 85 86 90.

Main host(s)

Western larch

Secondary host(s)

Amabilis fir, balsam fir, black spruce, Engelmann spruce, grand fir, ponderosa pine, Rocky Mountain Douglas-fir, shore pine, Sitka spruce, western hemlock, western white pine, white spruce