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Western Gall Rust
Endocronartium harknessii (J. P. Moore) Y. Hiratsuka
(= Peridermium harknessii J. P. Moore)
Basidiomycotina, Uredinales, Cronartiaceae
Hosts: Endocronartium harknessii is restricted to pine, specifically the two-needle, or 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, Austrian pines.
Distribution: Western gall rust is widespread throughout the province affecting susceptible trees throughout their range. Because the rust is found in eastern North America as well, the common names "pine-to-pine gall rust" or "globose gall rust" are sometimes used.
Identification: Western gall rust is characterized by the formation of woody swellings (galls) on branches and stems (Fig. 35a). Although the galls are generally globose, they may be asymmetrical and are sometimes deeply fissured. In the late spring (May-July, depending on climate), orange-coloured spores form in blisters beneath the bark of the galls (Fig. 35b). The bark generally sloughs off, exposing spores over much of the gall surface. For most of the year, however, galls are covered with normal bark.
Infection occurs through the succulent tissue of elongating shoots, so all galls are initially formed on one-year-old growth (Fig. 35c). Galls continue to increase in diameter as the host tree grows, and typically reach sizes of 5-10 cm in diameter (although larger galls sometimes develop on main stems). Galls become inactive with the death of the branch or stem, or are often killed by hyperparasitic fungi, but the woody swellings remain on the tree.
Microscopic Characteristics: Spermatia rare, in droplets on gall surface. Aecia and uredinia lacking. Peridermioid teliospores 1-celled, catenulate, oblong, obovate-oblong, or ellipsoid, 14-24 x 23-25 µm, verrucose with tapered columnar rods, wall colourless, spore colour provided by orange lipid bodies within cell, some spores with smooth area on one side (Fig. 35d). Teliospores resemble aeciospores of other Cronartium spp.
Damage: Damage is not significant on mature trees where most infections occur on branches. Branch galls do not result in serious growth losses. However, infections on young trees more often result in main stem galls that can cause stem malformations and predispose the tree to breakage in high winds or under heavy snow loads (Figs. 35e, 35f).
Remarks: Unlike the other important stem rusts, E. harknessii does not require an alternate host to complete its life cycle. Infection occurs directly from pine-to-pine. This allows rapid intensification of the disease when conditions optimal for infection occur. However, such conditions only occur every several years, resulting in "wave years" of infection and gall formation.
References:
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 35a: Branch and stem galls on lodgepole pine caused by E. harknessii.
Figure 35b: Endocronartium harknessii gall with orange spores produced beneath bark.
Figure 35c: Immature gall that has never produced spores on one-year old pine branch.
Figure 35d: Endocronartium harknessii spores.
Figure 35e: Main stem galls on nursery-produced pine seedlings.
Figure 35f: Stem breakage at the site of a western gall rust gall.