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Comparative Pathogenicity of Calonectria theae and Cylindrocladium scoparium to Leaves and Roots of Azalea. S. A. Alfieri, Jr., Assistant Director, Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Gainesville 32601; R. G. Linderman(2), R. H. Morrison(3), and E. K. Sobers(4). (2)Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; (3)Research Assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55101; and (4)Associate Professor of Plant Pathology, University of Georgia, College of Agriculture Experiment Stations, Coastal Plain Station, Tifton 31794. Phytopathology 62:647-650. Accepted for publication 19 January 1972. DOI: 10.1094/Phyto-62-647.

Calonectria theae was isolated from leaves, root, and stems of several greenhouse cultivars of azalea. Pathogenicity of this fungus was compared with that of Cylindrocladium scoparium to roots and leaves of three greenhouse and three hardy cultivars of azalea. No mortality occurred among plants grown for 2 months in soil artificially infested with either species. However, more plants grown in soil infested with C. scoparium showed smaller and/or discolored root systems than those grown in soil infested with C. theae. The leaves of all cultivars showed various degrees of susceptibility to both species. In general, C. scoparium was more virulent to leaves and roots than was C. theae. A morphological comparison of C. theae and C. crotalariae was made.

Additional keywords: Calonectria crotalariae, Candelospora theae, Cercosporella theae, Cylindrocladium crotalariae,Cylindrocladium theae, Rhododendron obtusum.