Response of Alnus tenuifolia to inoculation with Valsa melanodiscus

Abstract 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 ...