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Stability of Plasmid-Borne Antibiotic Resistance in Xanthomonas vesicatoria in Infected Tomato Leaves. Mingtan Lai, Plant Pathologist, Laboratory Services, Division of Plant Industry, California Department of Food and Agriculture, Sacramento, CA 95814; S. Shaffer(2), and N. J. Panopoulos(3). (2)Technician, Laboratory Services, Division of Plant Industry, California Department of Food and Agriculture, Sacramento, CA 95814; (3)Department of Plant Pathology, University of California, Berkeley, CA 94720. Phytopathology 67:1527-1530. Accepted for publication 19 July 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1527.

Plasmids RP4 and RK2 were maintained by Xanthomonas vesicatoria in infected tomato leaves which were kept up to 6 mo under a variety of environmental conditions. Only a small percentage (0 to 12%) of bacteria recovered from leaves of plants kept at 27 C or from detached leaves which were kept moist at 5 C for up to 6 wk after inoculation had lost the plasmids. Similary, 94 to 100% of the surviving bacteria in dried leaves stored at 5, 20, 35, and 45 C for up to 6 mo, retained the plasmids. In contrast, the plasmids were lost with high frequency from bacteria kept on slants at the above temperatures. These results indicate that the epidemiological stability of R plasmids in plant pathogenic bacteria may not be easily predictable on the basis of their stability in culture media. The apparent stability of R plasmids in plants infected with bacterial pathogens or plant debris in the absence of antibiotic selective pressure can contribute to their long-term maintenance.

Additional keywords: bacterial leaf spot of tomato, bacterial genetics.