Didymosphaeria oregonensis Goodd.
Ascomycotina, Dothideales, Didymosphaeriaceae
Hosts: Didymosphaeria oregonensis has been only been found on alder. In B.C., it has been reported on Sitka, mountain, and red alder.
Distribution: This fungus is widely distributed throughout the range of its hosts in B.C.
Identification: Spindle-shaped cankers are common on stems and branches of young alder trees. At the site of a canker, the stem is often swollen, with a band of rough bark encircling the stem (Fig. 42a). Bands of rough bark range from 1-60 cm in length.
Microscopic Characteristics: Pseudothecia black, globose, ostiolate, pseudoparenchymatous, 1 mm in diameter, immersed, single. Asci bitunicate, cylindric-clavate, 8-spored, 75-90 µm long. Ascospores greenish, ellipsoid, 1-septate, 18-21 x 7-9 µm. Pseudoparaphyses filiform, branched, septate.
Damage: The presence of this fungus appears to have little effect on the health or productivity of alder trees. Young trees are occasionally deformed and/or stunted when numerous cankers are present.
Remarks: The infection of alder by Didymosphaeria oregonensis is thought to be restricted to young trees, and the cankers cease to grow after the bark thickens with age. The rough bark remains, however, on the trunks of mature trees.
References:
Gooding, L. N. 1931. Didymosphaeria oregonensis, a new canker organism on alder. Phytopathology 21: 913-918.
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Figure 42a: Canker caused by Didymosphaeria oregonensis on red alder.