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Silver Leaf Disease
Chondrostereum purpureum (Pers.:Fr) Pouzar.
(= Stereum purpureum Pers.:Fr.)
Basidiomycotina, Aphyllophorales, Stereaceae
Hosts:Chondrostereum purpureum is very commonly found on angiosperms, less so on conifers. In B.C., it has been reported on red and mountain alder, paper birch, apple, trembling aspen, balsam and black poplar, horsechestnut, maple, most Prunus spp., willow, subalpine fir, white spruce, Douglas-fir, western redcedar, and western hemlock. Elsewhere in North America it has also been found on grand and amabilis fir, Amelanchier, Arbutus, Cotoneaster, hornbeam, hickory, hackberry, dogwood, quince, beech, tulip-tree, mountain ash, tupelo, Ostrya, London planetree, pear, oak, lilac, elm, and grape.
Distribution: This fungus is widely distributed throughout the range of its hosts in B.C.
Identification: The common name "silver leaf disease" refers to the silver or leaden luster of leaves that occurs on some hosts (e.g., apple and Prunus spp.) resulting from air spaces that form between epidermal and palisade cells. Affected leaves become brown at midribs and margins. Fruiting bodies are common on the dead wood of standing and fallen broadleaved trees, and on cut surfaces of slash. They are annual (often persisting from year-to-year), resupinate to semipileate, extending out 2-4 cm from the substrate, and often form in groups (Figs. 46a, 46b). The upper surface of the sporophore is tomentose, greyish-white to purple, indistinctly zoned with a light-coloured margin. The hymenial surface is smooth or slightly wrinkled, bright purple when fresh, brown-violet when old. Fruiting bodies are 1-2.5 mm thick with a black line visible in cross section.
The incipient stage of decay appears as a reddish-brown stain (Fig. 46c). As decay advances the stain disappears and the wood becomes bleached. In final stages of decay wood is dry, light in weight, and white-mottled to pale yellow in colour.
Microscopic Characteristics: Hyphae in fruiting body thin- to thick-walled, 2.5-4 µm in diameter, clamps. Basidiospores elliptical to cylindrical, hyaline, smooth, non-amyloid, 6.5-8 x 2.5-3.5 µm Growth in culture rapid, mat white to light buff, ovoid terminal vesicles, laccase positive. Stalpers: 1 3 (5) (6) 13 14 (15) 17 19 21 23 25 30 31 (37) 39 or (39) (42) 45 48 51 52 53 54 (60) 75 (82) 83 (88) 89 (94) 95 97 99.
Damage: The economic impact of the disease is greater on ornamental and orchard trees than on trees in a forestry setting. Chondrostereum purpureum is largely a saprophyte but can be a weak parasite on living hardwoods. Toxins produced by the fungus affect leaves, and on some hosts kill branches or entire trees. This fungus is currently being considered as a candidate for use as a biocontrol agent for hardwood stump sprouts.
Remarks: Other related fungi in the Stereaceae such as Amylostereum, Stereum, Columnocystis or Peniophora could be confused with old fruiting bodies of C. purpureum.
References:
Thomas, G. P. and D. G. Podmore. 1953. Studies in forest pathology. XI Decay in black cottonwood in the middle Fraser region, British Columbia. Can. J. Bot. 31: 675-692.
Wall, R. E. 1990. The fungus Chondrostereum purpureum as a silvicide to control stump sprouting in hardwoods. North. J. Appl. For. 7:17-19.
Figures
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Figure 46a: Fruiting bodies of Chondrostereum purpureum.
Figure 46b: Fruiting bodies of Chondrostereum purpureum.
Figure 46c: Stain associated with decay.