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Ecology and Epidemiology

Rifampin-Resistant Xanthomonas phaseoli var. fuscans and Xanthomonas phaseoli: Tools for Field Study of Bean Blight Bacteria. David M. Weller, Graduate Student, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; A. W. Saettler, Research Plant Pathologist, Bean Disease Investigations, Agricultural Research Service, U. S. Department of Agriculture, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 68:778-781. Accepted for publication 18 November 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-778.

Rifampin-resistant mutants of Xanthomonas phaseoli (Xp) and X. phaseoli var. fuscans (Xpf) were screened for similarity to wild-type isolates and their utility as tools for field study of bean blight bacteria. A mutant (R10) isolate of Xpf and one (Ra) of Xp were similar to wild types in numerous bacteriological tests, grew at rates identical to, and were as virulent as the wild types in bean leaves. The doubling time for R10 and Ra was about 11% longer than that for the wild types in buffered yeast-extract liquid medium. The rifampin-resistance marker permitted selective isolation of R10 and Ra from field-grown inoculated bean leaves; growth of all phyllosphere bacteria was inhibited on media with rifampin (50 μg/ml). Addition of cycloheximide at 25 μg/ml reduced growth of resident yeasts and fungi. The rifampin resistance marker was stable when the bacteria were grown in culture or beans; no reversions to rifampin sensitivity have been detected.