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Stalactiform Blister Rust
Cronartium coleosporioides Arthur
(=Cronartium stalactiforme Arth. & Kern)
Basidiomycotina, Uredinales, Cronartiaceae
Hosts: Cronartium coleosporioides is restricted to pine, specifically the two- and three-needle, "hard" pines. In B.C., it is found on lodgepole, ponderosa, and jack pine in natural forests, and on any of the introduced hard pines including bishop, mugo, Monterey, Scots, and Austrian pines. The main alternate hosts are paintbrush (Fig. 31a), and cow-wheat (Fig. 31b). Other alternate hosts that have been identified by artificial inoculation are: yellow owl's clover, bracted lousewort, and yellow-rattle.
Distribution: This fungus is found throughout the range of its hosts in B.C., but is limited to areas where both aecial and telial hosts occur.
Identification: Perennial cankers, which form on stems and branches of the pine host, are generally elongate (up to and over 10 times longer than broad), diamond-shaped, and often girdle smaller stems and branches (Figs. 31c, 31d). Bark tissue may be thickened resulting in fusiform swelling. During late spring and summer, aecia appear as white-orange blisters that release orange aeciospores. During other times of the year, C. coleosporioides infections may be identified by their size, shape, and by sunken, dead bark and resinosis associated with the cankers. Porcupines and other rodents often preferentially chew on cankers during the winter leaving exposed wood (Fig. 31e).
Microscopic Characteristics: Spermatia and aecia on pine caulicolous, spermatia ovoid. Aecial filaments on inner surface of peridium pendant (Fig. 31f). Aeciospores orange, ellipsoid, 17-24 x 23-34 µm, verrucose with a conspicuous smooth spot and warts up to 3 µm high (Fig. 31g).
Urediospores on Castilleja globose-ellipsoid, 14-22 x 17-27 µm, orange, sparsely echinulate, not produced by all races. Teliospores oblong, 12-17 x 30-52 µm, colourless, smooth.
Damage: Mortality may occur as a result of girdling of small diameter stems, and as such can act as a natural thinning agent in young stands. In older trees stem defects occur, reducing wood quality and predisposing trees to damage from wind and heavy snow. Atropellis piniphila is often associated with stalactiform blister rust cankers.
Remarks:Cronartium coleosporioides can be distinguished from C. comandrae by its more elongate cankers, and more precisely by its ellipsoid aeciospores (cf. pear-shaped aeciospores of C. comandrae). Differentiating between C. coleosporioides and C. comptoniae is more difficult. The longitudinal hypertrophied ridges produced by sweet fern blister rust are not present on stems infected by stalactiform blister rust. In addition, the aecial filaments of C. comptoniae are continuous, whereas those of C. coleosporioides are pendant. Identifying the presence of the alternate hosts will also help distinguish between these two rusts. Non-sporulating cankers may also be confused with those caused by Atropellis piniphila.
References:
Peterson, R. S. and F. F. Jewell. 1968. Status of American stem rusts of pine. Ann. Rev. Phytopathol. 6: 23-40.
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 31a: Indian paint brush, telial host of Cronartium coleosporioides.
Figure 31b: Cow wheat, telial host of Cronartium coleosporioides.
Figure 31c: Aecial pustules on lodgepole pine stems and branches.
Figure 31d: Aecial pustules on lodgepole pine stems and branches.
Figure 31e: Squirrel damage on a sporulating C. coleosporioides canker.
Figure 31f: Pendant aecial filaments characteristic of C. coleosporioides.