Morphology, Cultural Characteristics, and Pathogenicity of Rhizosphaera kalkhoffii on Picea spp. in Northern Minnesota and Wisconsin. Jennifer Juzwik, Research Plant Pathologist, USDA Forest Service, North Central Forest Experiment Station, 1992 Folwell Avenue, St. Paul, MN 55108. . Plant Dis. 77:630-634. Accepted for publication 16 February 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-0630.

Morphology, cultural characteristics, and pathogenicity of Rhizosphaera kalkhoffii from spruce (Picea spp.) showing premature needle loss in northern Minnesota and Wisconsin were investigated. Pycnidiospores from needles, conidia of the Hormonema-like synanamorph, and pycnidiospores produced in culture were similar for Colorado blue, Engelmann, Norway, and white spruce collections and isolates. Pycnidiospores from black spruce needles were smaller than those from Colorado blue or white spruce (P < 0.05). Colony diameters at 14 days were similar on four different spruce needle extract agars for isolates from Colorado blue, Engelmann, and white spruce. Growth profiles of the fungus from Colorado blue, Engelmann, and white spruce on three agar media at five temperatures, and in three liquid media at three temperatures, were also similar to each other, with optimum growth occurring at either 20 or 25 C. Needle cast symptoms and R. kalkhoffii pycnidia developed within 12 mo on black, Colorado blue, Norway, and white spruce after inoculation with pycnidiospores of an isolate of the fungus from either Colorado blue or white spruce.