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Histopathology of Immune and Susceptible Cotton Cultivars Inoculated with Xanthomonas malvacearum. Edward T. Cason, Jr., Langston University, Langston, OK 73050; P. E. Richardson(2), L. A. Brinkerhoff(3), and R. K. Gholson(4). (2)(4)Oklahoma State University, Stillwater, OK 74074; (3)Langston University, Langston, OK 73050. Phytopathology 67:195-198. Accepted for publication 24 August 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-195.

Histological observations showed that, with large doses of inoculum, damage to immune host tissue occurred within 4-6 hr after inoculation. Chloroplast damage, cell compression, and tissue shrinkage followed by necrosis and desiccation were the most obvious features of the hypersensitive response. The susceptible cultivar exhibited none of these responses; the pathogen directly disintegrated host cells and produced foliar lesions. A direct relationship between inoculum concentration and a cellular staining phenomenon was observed in the immune cultivar. Thick sections of plastic embedded tissue showed bacteria localized among host cells. High numbers of bacteria were found in sub-stomatal cavities and between palisade and spongy parenchyma cells. Growth of the pathogen in the immune host tissue occurred during the hypersensitive reaction with the resultant appearance of localized colonies of bacteria in polysaccharide slime among necrotic host cells.

Additional keywords: plasmolysis, flaccid, intensely-stained, water-soaked, tissue-shrinkage.