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Response of Soybean Foliage to Reciprocal Challenges by Ozone and a Hypersensitive-Response-Inducing Pseudomonad. E. J. Pell, Assistant Professor, Department of Plant Pathology and the Center for Air Environment Studies, The Pennsylvania State University, University Park, PA 16802; F. L. Lukezic(2), R. G. Levine(3), and W. C. Weissberger(4). (2)(3)(4)Professor, Research Assistant, and Research Aide, respectively, Department of Plant Pathology and the Center for Air Environment Studies, The Pennsylvania State University, University Park, PA 16802. Phytopathology 67:1342-1345. Accepted for publication 16 May 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1342.

Primary leaves of soybean inoculated with a concentration of bacteria which elicited a low level of hypersensitive response (HR) were subsequently challenged with an ozone dose which induced a severe water-soaking symptom in noninoculated foliage. Leaves inoculated with bacteria 24 hr prior to ozone exposure exhibited significant reduction in ozone symptoms. Leaves inoculated with bacteria 4 hr prior to ozone exposure displayed an enhanced response. The response to the interaction was unique and was characterized by some properties of each stress. Soybean plants were exposed to a dose of ozone which elicited a slight flecking response and inoculated 24, 48, 96, 144, and 168 hr after exposure with bacterial concentrations sufficient to cause severe HR. Ozone-treated plants did not display the bacteria-induced HR at any inoculation times. The absence of significant differences between ozone-treated and control plants at 168 hr probably was due to increased resistance of the host to the bacteria with increasing leaf age.