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Valsa melanodiscus (anamorph Cytospora umbrina) has been associated with cankers, dieback, and death of alder (Alnus) stems in western North America. To determine the ability of this fungus to induce these symptoms, the responses of thinleaf alder (Alnus tenuifolia) stems to inoculation with V. melanodiscus were studied in field locations in Alaska and on plants in a greenhouse. In the field, woody stems were wounded to expose both inner bark and sapwood and inoculated in early May 2007 or September 2007 by placing a colonized agar plug over the wound. Sunken, elongated cankers that developed on inoculated stems in the field closely resembled those attributed to natural infection of thinleaf alders by V. melanodiscus. In contrast, wounded control stems exhibited strong callus production and wound closure. In the greenhouse, actively growing lateral shoots were inoculated by placing a colonized agar plug over a fresh leaf scar. Inoculation in the greenhouse resulted in development of cankers, and ...

An epidemic of cytospora canker [Valsa melanodiscus, anamorph Cytospora umbrina] is associated with dieback and mortality of Alnus incana ssp. tenuifolia in the Southern Rocky Mountains and had begun by the late 1980s. Isolations showed that inoculum was often abundant on bark and bud surfaces even in winter, especially near diseased stems. The pathogen was occasionally isolated from internal tissues of dormant buds and asymptomatic wood and phloem. In infected stems, the pathogen was detected up to 5 cm beyond visible canker margins. The data suggest that the pathogen can cause latent infections, but the infection court remains unclear. Inoculations of healthy stems in the field did not induce canker formation. Fruiting of the anamorph was primarily in late winter and spring, and sexual maturation occurred in late summer and fall. Stem age and growth data support earlier conclusions that the mortality does not represent a steady-state condition with normal attrition of older stems. Canker expansion and k...