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Decreased Hypersensitivity to Xanthomonads in Pepper after Inoculations with Virulent Cells of Xanthomonas vesicatoria. R. E. Stall, Department of Plant Pathology, University of Florida, Gainesville 32611; J. A. Bartz(2), and A. A. Cook(3). (2)(3)Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 64:731-735. Accepted for publication 17 December 1973. DOI: 10.1094/Phyto-64-731.

Living cells of a virulent strain of Xanthomonas vesicatoria decreased hypersensitivity in pepper leaf tissue to an avirulent strain of the organism. Moreover, reduced hypersensitivity occurred only when cells of the virulent strain were injected into pepper leaves prior to injections with the avirulent cells. The attenuation of hypersensitivity increased with time between inoculations. The virulent cells of X. vesicatoria decreased hypersensitivity initiated by some other xanthomonads, but not by some species of Pseudomonas. Heat-killed cells of X. vesicatoria were also effective in reducing hypersensitivity initiated by avirulent cells of the same organism. It was theorized that a zone of influence was exerted on the host cells by the virulent bacteria and that the zone increased with time of incubation. Hypersensitivity initiated by avirulent cells was prevented, if avirulent cells were deposited in the zone of influence, but not if they were deposited elsewhere on the cell surface.