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Ecology and Epidemiology

Sources of Primary Inoculum of Botrytis squamosa. L. A. Ellerbrock, Graduate Research Assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853; J. W. Lorbeer, Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853. Phytopathology 67:363-372. Accepted for publication 2 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-363.

Sclerotia-bearing conidia of Botrytis squamosa were found on onion bulbs and leaf debris in cull piles and seed production fields in April and May and on the surface of organic soil from April through July in fields cropped to onions in Orange County, New York. Sclerotia produced conidia in the laboratory over a range of 3-27 C (optimum 9 C) and produced four successive crops of conidia in repeated germination tests. Apothecia of B. squamosa were observed in April on sclerotia associated with onion leaf debris on the surface of soil in fields previously cropped to onions. Ascospores from these apothecia were pathogenic to onion leaves. Dormant sclerotia covered with 10-15 cm of soil in April produced apothecia when uncovered at different times from late May through July. Botrytis squamosa frequently was isolated from lesions on leaves of sprouted bulbs in cull piles and seed production fields in late May and early June. Conidia of B. squamosa were trapped from the air over cull piles and seed production fields 2-4 wk prior to the appearance of Botrytis leaf blight in commercial onion fields in 1971-73. Cull piles and seed production fields are, therefore, important sources of primary inoculum for initiation of Botrytis leaf blight epidemics in commercial onion fields in Orange County. Elimination or reduction of these sources of inoculum should delay the development of leaf blight epidemics.