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Ozone and Botrytis Interactions in Onion-Leaf Dieback: Open-Top Chamber Studies. R. T. Wukasch, Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1; G. Hofstra, Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. Phytopathology 67:1080-1084. Accepted for publication 4 March 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1080.

Paired open-top chambers were used to study interactions between Botrytis spp. and ozone in field-grown onions. Charcoal filters removed 35 to 65% of the ambient ozone, resulting in six-fold reduction of onion leaf dieback and a 28% increase in onion yield compared with unfiltered chambers. Symptoms of leaf injury appeared soon after ozone levels exceeded 294 μg/m3 (0.15 ppm) for 4 hr. Lesions caused by Botrytis were few because no dew formed in the chambers. However, when leaves were wetted with foggers, inoculation with mycelial suspensions of B. squamosa in late August produced significantly more lesions and leaf dieback in the unfiltered chamber. Botrytis squamosa, B. cinerea, B. allii, and several genera of secondary fungi were isolated from these lesions. Botrytis squamosa was recovered from lesions only, whereas B. cinerea and B. allii were associated more generally with onion leaf tissue regardless of lesions.

Additional keywords: Yield loss, onion, blast, open-top chambers.