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Isolate Characteristics and Epidemic Components of Leptosphaerulina Leaf Spots on Alfalfa and White Clover. Ocen Modesto Olanya, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, Present address: International Institute of Tropical Agriculture, Oyo Road, PMB 5320, Ibadan, Nigeria.; C. Lee Campbell, Associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 80:1278-1282. Accepted for publication 21 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1278.

Isolates of Leptosphaerulina spp. from alfalfa (Medicago sativa) and white clover (Trifolium repens) were compared for growth rate on V-8 juice medium at 12?28 C, colony characteristics, production of pseudothecia, ascospore morphology, and pathogenicity on alfalfa and white clover. Optimum growth rate occurred at 20?24 C. Isolates from white clover generally had slower, restricted growth with irregular colony margins on agar medium, whereas isolates from alfalfa generally grew rapidly with regular colony margins. Production of pseudothecia, ascospore characteristics, and pathogenicity on detached leaves of alfalfa and white clover were similar among isolates. The conspecificity of L. briosiana and L. trifolii was supported. Under controlled-environment conditions, disease severity was lower at 30 C than at 22 or 15 C. At all temperatures, mean disease severity was similar for white clover and alfalfa when inoculated with isolates of L. trifolii from white clover, but was greater on alfalfa than on white clover with isolates from alfalfa. Disease severity was similar among isolates tested from each host. Mean incubation period (3?4 days), latent period (14?15 days), and infectious period (21 days) were similar, but sporulation varied among isolate-host combinations.