Cronartium comandrae Peck
Basidiomycotina, Uredinales, Cronartiaceae
Hosts: The aecial hosts are 2- and 3- needle hard pines, including lodgepole and ponderosa pine, The telial hosts are California Comandra (C. umbellata (L.) Nutt.) (Fig. 32a) and Bastard toadflax (Geocaulon lividum (Richardson) Fernald) (Fig. 32b).
Distribution: Throughout host range in B.C., but limited to areas where both aecial and telial hosts occur.
Identification: On pines, the rust causes swelling, cracking, and marginal resinosus of bark on stems and branches, forming elongate, sometimes diamond-shaped cankers (Fig. 32c). Perennial cankers grow both vertically and radially, and can girdle stems resulting in the death of tissues distal to the infection. Spermogonial (Fig. 32d) and aecial pustules form within the boundaries of the cankers, producing orange spores in the spring and early summer (Fig. 32e). Uredinia (Fig. 32f) and telia (Fig. 32g) are produced on leaves and stems of the herbaceous alternate hosts in mid to late summer.
Microscopic Characteristics: Spermagonia and aecia caulicolous. Spermatia pear-shaped. Aeciospores are orange, finely verrucose, 19-24 x 32-66 µm, with a characteristic pear-shape (Fig. 32h). Urediniospores 20-23 x 22-28 µm, teliospores produced in prominent orange-brown telial columns, 12-15 x 32-44 µm.
Damage: Trees of all sizes and ages are affected, and the presence of cankers can result in growth defects and mortality. Outbreaks of this disease are sporadic, due to variations in the distribution of the alternate host and the periodicity of environmental conditions necessary for infection. The most serious damage has been observed in nurseries and plantations where rapid stem girdling results in high mortality.
Remarks: The aecial cankers of comandra blister rust are very similar in appearance to those of sweet-fern and stalactiform rusts. However, examination of the uniquely shaped aeciospores with a microscope or even a hand-lens will distinguish this rust from others. Swellings on seedlings might be confused with pre-sporulating gall of Endocronartium harknessii; however, C. comandrae swellings result from swollen bark, while E. harknessii galls have normal bark over abnormally thickened xylem tissue.
Hiratsuka, Y. and J. M. Powell. 1976. Pine stem rusts of Canada. Can. For. Serv., NFRC, For. Tech. Rep. 4.
Krebill. R. G. 1968. Cronartium comandrae in the Rocky Mountain states. USDA For. Serv., Res. Paper INT-50. Ogden, UT.
Ziller, W. G. 1974. The tree rusts of western Canada. Can. For. Serv., Publ. No. 1329. Victoria, B.C.
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Figure 32a: California comandra, telial host of Cronartium comandrae.