MORPHOLOGY, CULTURAL-CHARACTERISTICS, AND PATHOGENICITY OF RHIZOSPHAERA-KALKHOFFII ON PICEA SPP IN NORTHERN MINNESOTA AND WISCONSIN

Morphology, cultural characteristics, and pathogenicity of Rhizosphaer a kalkhoffii from spruce (Picea spp.) showing premature needle loss in northern Minnesota and Wisconsin were investigated. Pycnidiospores fr om needles, conidia of the Hormonema-like synanamorph, and pycnidiospo res produced in culture were similar for Colorado blue, Engelmann, Nor way, and white spruce collections and isolates. Pycnidiospores from bl ack spruce needles were smaller than those from Colorado blue or white spruce (P < 0.05). Colony diameters at 14 days were similar on four d ifferent spruce needle extract agars for isolates from Colorado blue, Engelmann, and white spruce. Growth profiles of the fungus from Colora do blue, Engelmann, and white spruce on three agar media at five tempe ratures, and in three liquid media at three temperatures, were also si milar 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 inoculatio n with pycnidiospores of an isolate of the fungus from either Colorado blue or white spruce.