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Reduction of Pith Maceration by Erwinia chrysanthemi in Chrysanthemum Cuttings Infected With Chrysanthemum Stunt Viroid. Ann Finer Silverglate, Former research assistant, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Robert S. Dickey(2), and R. K. Horst(3). (2)(3)Professor, and associate professor, respectively, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 70:135-139. Accepted for publication 27 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-135.

Cuttings of Chrysanthemum morifolium ‘Bonnie Jean,’ either healthy or artificially infected with chrysanthemum stunt viroid (CSV), were dipinoculated with Erwinia chrysanthemi strain 159. Infection by CSV reduced the amount of bacterial pith maceration, which was determined by measuring the length of maceration from the base of the cutting. A decrease in maceration coincided with the occurrence of viroid symptoms on the leaves and/or the detection of CSV RNA by polyacrylamide gel electrophoresis. Differences between healthy and CSV-infected stems were not noted by histological examination between 10 and 41 days after inoculation with CSV. Erwinia chrysanthemi was restricted to xylem vessel elements in CSV-infected cuttings 5 days after inoculation with the bacterium, whereas bacteria spread from the vessel elements to the adjacent vascular cells and into the pith tissue of healthy cuttings.