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Ecology and Epidemiology

The Role of Phyllosphere Bacteria in Pathogenesis by Botrytis squamosa and B. cinerea on Onion Leaves. C. A. Clark, 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 67:96-100. Accepted for publication 27 July 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-96.

Numbers of lesions formed by Botrytis squamosa on onion leaves were reduced only slightly by two of thirteen onion leaf surface bacteria. Ten of the isolates stimulated greater frequency of lesion formation. Conidial germination of B. squamosa and B. cinerea in water in vitro was inhibited by several of the bacteria. Most of the isolates did not inhibit germination in nutrients. Two bacterial isolates were selected as potential nutrient competitors based on their ability to inhibit germination of the two Botrytis species in water, but not in nutrients. They grew equally as well on leaves inoculated with B. squamosa or B. cinerea as on noninoculated leaves. The same isolates grew moderately well in vitro in cell-free diffusates of conidia of both pathogens, but poorly in suspensions of conidia. Treatment of leaves with antibiotics (streptomycin, penicillin, chloramphenicol, or penicillin plus chloramphenicol) reduced natural bacterial populations. None of the antibiotics stimulated lesion formation on onion leaves following inoculation by B. cinerea or B. squamosa conidia in water suspension.