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Formation of Microsclerotia of Cylindrocladium spp. in Infected Azalea Leaves, Flowers, and Roots. R. G. Linderman, Research Plant Pathologist, Northeastern Region, ARS, USDA, Beltsville, Maryland 20705; Phytopathology 63:187-191. Accepted for publication 25 July 1972. DOI: 10.1094/Phyto-63-187.

Lesions on attached azalea leaves infected with Cylindrocladium scoparium, C. theae, or C. floridanum contained pigmented hyphae or cells, but no microsclerotia. Following abscission, each species of Cylindrocladium rapidly invaded the entire leaf when held at a high relative humidity. Cylindrocladium scoparium and C. floridanum formed abundant microsclerotia in leaf mesophyll parenchyma within 2 weeks after abscission, whereas C. theae formed relatively few. Microsclerotia were not specifically associated with stomata. Both C. theae and C. floridanum produced sclerotiumlike stromata in leaves on which perithecia of their Calonectria stages developed. Flower tissues infected with each of the three Cylindrocladium spp. contained microsclerotia and smaller, thick-walled, pigmented cell aggregates. Perithecia of C. theae and C. floridanum were observed on the stamens of infected flowers. Azalea roots infected with C. scoparium or C. floridanum, examined after the onset of wilt symptoms, contained relatively few microsclerotia. Roots infected with C. theae contained some small, pigmented cell aggregates, but no microsclerotia.

Additional keywords: survival structures, flower blight, leaf spot, root rot, azalea wilt.