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Spruce Cone Rusts
Inland spruce cone rust
Chrysomyxa pirolata G. Wint. in Rabenh.
Coastal spruce cone rust
Chrysomyxa monesis Ziller
Basidiomycotina, Uredinales, Coleosporiaceae
Hosts: In B.C., the aecial hosts of Chrysomyxa pirolata are limited to spruce species, including Engelmann, white, black, Colorado, and Sitka spruce. Elsewhere in North America it has been reported on red spruce. The telial hosts include single delight and a number of species of wintergreen where the rust is systemic and perennial.
Chrysomyxa monesis is restricted to Sitka spruce as an aecial host and single delight as a telial host.
Distribution:Chrysomyxa pirolata is found throughout the province, whereas C. monesis occurs only at the coast on spruce and both at the coast and in the interior on single delight.
Identification:Chrysomyxa pirolata and C. monensis attack only the cones of spruce, not the needles. Infected cones turn brown prematurely and are easily identified by the presence of orange-coloured aeciospores, which form between the cone scales in late summer (Figs. 30a, 30b, 30c). A light "dusting" of aeciospores is often observed on vegetation beneath trees with diseased cones. Yellow uredinia are present on the lower leaf surfaces, and sometimes on the petioles of the telial hosts (Figs. 30d, 30e). Chrysomyxa pirolata-infected leaves of Pyrola spp. are slightly chlorotic, more erect, and the upper surface is less shiny than that of healthy leaves. Chrysomyxa monensis-infected Moneses uniflora plants may be slightly chlorotic, but commonly show no symptoms.
Microscopic Characteristics:
Chrysomyxa pirolata: Spermogonia and aecia on cone scales, aecia yellow-orange. Aeciospores broadly ellipsoid, clear, thick walls, warts depressed, forming a reticulate pattern, 17-35 x 22-37 µm (Fig. 30f). Uredinia hypophyllous, systemic, round, yellowish-red. Urediniospores with yellow contents, ellipsoid, clear walls with warts resembling those of aeciospores, 13-24 x 19-33 µm. Telia hypophyllous, flat, orange-brown.
Chrysomyxa monensis: Spermogonia and aecia on cone scales, aecia yellow-orange. Aeciospores broadly ellipsoid, clear, thick walls, warts narrow, deeply fluted, 17-25 x 29-45 µm. Uredinia hypophyllous, systemic, round, yellowish-red. Urediniospores with yellow contents, ellipsoid, clear walls with warts resembling those of aeciospores, 15-22 x 23-34 µm. Telia hypophyllous and on petioles, waxy, yellow turning brown with age.
Damage: These rusts periodically damage cones in localized forest areas and can be a serious problem in spruce seed orchards.
Remarks: Seeds are not usually formed in diseased cones, and even when they are produced, malformation and resinosis of the cones hinder seed dispersal or extraction. Those seeds that are formed tend to weigh less and have poor germination.
References:
Sutherland, J. R., T. Miller, and R. S. Quinard. 1987. Cone and seed diseases of North American conifers. N. Am. For. Commis., Publ. No.1.
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 30a: Chrysomyxa pirolata aeciospores produced beneath the cone scales of spruce cones.
Figure 30b: Chrysomyxa pirolata aeciospores produced beneath the cone scales of spruce cones.
Figure 30c: Chrysomyxa pirolata aeciospores produced beneath the cone scales of spruce cones.
Figure 30d: Chrysomyxa pirolata uredinia on the lower surface of a wintergreen leaf.
Figure 30e: Orange-yellow urediniospores produced in uredinial pustules.