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Vertical Distribution of Sclerotia of Sclerotium cepivorum and Host Root Systems Relative to White Rot of Onion and Garlic. 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 66506; D. H. Hall, extension plant pathologist, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 70:70-73. Accepted for publication 24 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-70.

Sclerotia of Sclerotium cepivorum placed 30 cm deep in beds in the field germinated and infected garlic bulbs. Mycelium grew upward on roots and hyphae radiated 12 cm into soil, frequently infecting nearby roots. Leaves wilted and plants died only when the pathogen grew onto the stem plate and leaf sheaths. Masses of sclerotia formed as leaf sheaths decayed. Few sclerotia formed in roots. Mycelium spread most rapidly from plant to plant 24 cm below the stem plates where roots grew laterally and root density was highest. Infections 1 cm or closer to the stem plate rarely resulted in disease of adjacent plants because downward movement of mycelium on roots was limited and few roots of neighboring plants grew laterally in this zone. The extent of plant-to-plant disease spread depended on timing and depth of infection. The greatest disease incidence resulted from inoculum placed at intermediate depths and from early infections.

Additional keywords: Allium cepa, Allium sativum, disease development.