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Genetics

Ascospore Dimorphism in Sclerotinia trifoliorum and Cultural Characters of Strains from Different-Sized Spores. J. Y. Uhm, Former research assistant, Plant Pathology, Tokyo University of Agriculture, Tokyo, 156, Japan, Present address: Assistant professor, Department of Agricultural Biology, College of Agriculture, Kyungpook National University, Daegu, 635, Korea; H. Fujii, professor, Plant Pathology, Tokyo University of Agriculture, Tokyo, 156, Japan. Phytopathology 73:565-569. Accepted for publication 28 October 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-565.

Among five isolates of Sclerotinia trifoliorum from different sources, all mature asci displayed ascospore dimorphism, with 4:4 segregation of large and small ascospores, arranged in six types of first and second meiotic division segregation. The second meiotic division frequency (mean = 20.8%) did not vary significantly among isolates. This indicated that dimorphism in spore size was regulated by the same allelic pair in all isolates. The strains derived from the large and small ascospores of an ascus were very similar in morphology, growth rate, and pathogenicity. Without exception, nonpaired cultures from single-ascosporic strains derived from small spores failed to produce apothecia, whereas those derived from large spores produced sporulating apothecia, although their asci again exhibited 4:4 segregation for spore size.