Ultrastructural Effects of Ozone on the Host-Parasite Relationship of Botrytis cinerea and Pelargonium hortorum

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Abstract
Scanning electron microscopy (SEM) was used to observe effects of ozone on florist''s geranium (P. hortorum) inoculated and noninoculated with the gray mold disease fungus, B. cinerea. Greenhouse-grown geranium plants of cultivar Sincerity were exposed to either ozone-free air, 299 .mu.g/m3 [0.15 ppm (vol/vol)] ozone for 10 days for 6 h/day, or 1398 .mu.g/m3 (0.70 ppm ozone) for two 6 h periods 24 h apart. Plants inoculated with B. cinerea were exposed to filtered air or ozone at 299 .mu.g/m3 (0.15 ppm) for two 6 h periods 24 h 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 1398 .mu.g 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.
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