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Large-Spored Spruce-Labrador Tea Rust
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Chrysomyxa ledicola Lagerh.
Basidiomycotina, Uredinales, Coleosporiaceae
Hosts: The aecial hosts of Chrysomyxa ledicola in B.C. include white, black, Sitka, and Englemann spruce. The telial hosts are Labrador-tea and northern Labrador-tea.
Distribution: This disease is common throughout the province and affects spruce in areas where the alternate host is present. Its occurrence on Ledum, however, is not restricted to areas where spruce occurs.
Identification:Chrysomyxa ledicola is the most common of the non-brooming needle rusts of spruce. Blister-like aecia form on current years needles, and occasionally on cone scales, producing orange-coloured aeciospores throughout the summer (Figs. 29a, 29b). C. ledicola is easily recognized on the alternate host, Labrador-tea, since it is the only rust that produces uredinia on the upper surface of the leaves (Fig. 29c).
Microscopic Characteristics: Spermogonia amphigenous, aecia hypophyllous; on current years needles, rarely on cone scales. Aecia orange with fragile white peridium. Aeciospores broadly ellipsoid, 22-34 x 27-46, walls colourless, 3-6 µm thick, coarsely verrucose, warts stellate in surface view. Uredinia and telia epiphyllous on previous years foliage. Uredinia orange. Urediniospores broadly ellipsoid or globoid, 20-33 x 24-45 µm, wall colourless, 1.4-4.8 µm thick, warts nearly cylindrical to fluted. Telia epiphyllous, flat, 10-24 x 13-18 µm, wall colourless, uniformly 1 µm thick.
Damage: Severe defoliation of spruce occurs in localized areas, particularly when moist environmental conditions prevail.
Remarks: A similar rust on spruce, small-spored spruce-Labrador-tea rust, caused by Chrysomyxa ledi de Bary var. ledi, differs from C. ledicola in that its aeciospores are smaller (13.5-25 x 18-32 µm) and that uredinia form on the lower surface of Ledum leaves.
References:
Savile, D. B. O. 1950. North American species of Chrysomyxa. Can J. For. Res. 28:318-330.
Ziller, W. G. 1974. The tree rusts of western Canada. Can. For. Serv., Publ. No. 1329. Victoria, B.C.
Figures
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Figure 29a: Chrysomyxa ledicola aecia on spruce needles.
Figure 29b: Chrysomyxa ledicola aecia on spruce needles.
Figure 29c: Chrysomyxa ledicola uredinia on the upper surface of Labrador-tea leaves.