Rifampin-Resistant Xanthomonas phaseoli var. fuscans and Xanthomonas phaseoli: Tools for Field Study of Bean Blight Bacteria

Abstract

Rifampin-resistant mutants of X. 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 (R 10) 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 .mu.g/ml). Addition of cycloheximide at 25 .mu.g/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 were detected.