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Soil Temperature and Moisture Effects on Sclerotium Germination and Infection of Onion Seedlings by Sclerotium cepivorum. F. J. Crowe, Formerly graduate research assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Extension Plant Pathology, Kansas State University, Manhattan, KS 66506; D. H. Hall, extension plant pathologist, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 70:74-78. Accepted for publication 24 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-74.

Germination of sclerotia of Sclerotium cepivorum in soil dampened with and without garlic extract was optimal at 18 C and 300 millibars (mb) matric potential (field capacity). Seventy-eight percent of sclerotia germinated with extract and 16% germinated without extract. Germination was confined to temperatures between 9 and 24 C at 300 mb and between 12.5 mb and 3 bars at 18 C. Interactions between temperature and soil moisture were more apparent at less optimum temperature and soil moisture combinations. Germination varied more with matric potential than with moisture content of two different soils. Only 0.4% of germinating sclerotia formed secondary sclerotia in soil. Decay of sclerotia was similar in soil with and without garlic extract and was directly proportional to increasing temperature and increasing soil moisture. Infection of host plants by sclerotia was confined to temperatures between 6 and 24 C and 45 mb and 3 bars matric potential. Disease developed more rapidly with increasing temperature within the 624 C range, but developed at the same rate for all permissive matric potentials at a given temperature.

Additional keywords: Allium cepa, Allium sativum, white rot.