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The Role of Dew and Temperature in the Epidemiology of Botrytis Leaf Blight of Onion. P. B. Shoemaker, Former Research Assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Senior Author present address: Associate Professor, Department of Plant Pathology, North Carolina State University, Mountain Horticultural Crops Research Station, Fletcher, NC 28732; J. W. Lorbeer, Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 67:1267-1272. Accepted for publication 30 March 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1267.

Numerous leaf blight lesions developed within 48 hr on intact onion leaves which remained wet continuously for at least 6 hr in a dew chamber at 20 1 C following inoculation with conidia of Botrytis squamosa. Lesion numbers increased significantly for each additional 2-hr increment of leaf wetness when tested to 18 hr. When conidia were brushed onto dry leaf surfaces which remained dry in an atmosphere of 92% relative humidity, lesions did not develop. Leaf blighting increased for each 12-hr increment in dew period from 12 to 60 hr after inoculation. Lesion numbers and leaf blighting were significantly greater on older leaves than on younger leaves. Lesions developed over a range of 9 to 23 C after exposure of plants to a leaf wetness period of 40 hr at constant temperatures ranging from 7 to 30 C. Germination of conidia was maximum at 15 C, and it occurred over the range of 12-27 C; growth in culture was maximum at 24 C, and it occurred from 9-31 C.

Additional keywords: Allium cepa, etiology, Botrytis squamosa.