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Ultrastructural Effects of Ozone on the Host-Parasite Relationship of Botrytis cinerea and Pelargonium hortorum. Charles R. Krause, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Nursery Crops Research Laboratory, Delaware, OH 43015; T. Craig Weidensaul, Director, Laboratory for Environmental Studies and Associate Professor of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster, OH 44691. Phytopathology 68:301-307. Accepted for publication 12 September 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-301.

Scanning electron microscopy (SEM) was used to observe effects of ozone on floristís geranium (Pelargonium hortorum) inoculated and noninoculated with the gray mold disease fungus, Botrytis cinerea. Greenhouse-grown geranium plants of cultivar Sincerity were exposed to either ozone-free air, 299 μg/m3 [0.15 ppm (v/v)] ozone for 10 days for 6 hr/day, or 1,398 μg/m3 (0.70 ppm ozone) for two 6-hr periods 24 hr apart. Plants inoculated with Botrytis cinerea were exposed to filtered air or ozone at 299 μg/m3 (0.15 ppm) for two 6-hr periods 24 hr apart. Fresh leaf samples from each treatment were examined by SEM. Non-ozonized, noninoculated leaf tissues were distinguished from ozonized, chlorotic, prematurely senescent leaf tissues by SEM on the basis of cuticular features. Premature senescence was characterized by ruptured guard cells. Tissues subjected to 1,398 μg ozone/m3 (0.70 ppm ozone) exhibited abaxial necrotic lesions; epidermal cells appeared smooth and without definite cell boundaries. Sporulation and germination of conidia, and hyphal penetration by, B. cinerea were readily observed by SEM on non-ozonized, inoculated geraniums. Neither hyphal penetration, sporulation, nor germination of conidia was observed on ozonized, inoculated leaves. A flocculence of unknown composition covered ozonized, inoculated specimens.

Additional keywords: scanning electron microscopy, ozone injury.