Tween Media for Semiselective Isolation of Xanthomonas campestris pv. vesicatoria from Soil and Plant Material. Raymond G. McGuire, Postdoctoral Associate, Department of Plant Pathology, University of Florida, Gulf Coast Research and Education Center, Bradenton 34203. Jeffrey B. Jones, Assistant Professor, Department of Plant Pathology, University of Florida, Gulf Coast Research and Education Center, Bradenton 34203, and Myron Sasser, Professor, Department of Plant Science, University of Delaware, Newark 19711. Plant Dis. 70:887-891. Accepted for publication 20 March 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-887.

Three semiselective culture media have been developed for the isolation of Xanthomonas campestris pv. vesicatoria (X. c. pv. vesicatoria) from soil and plant material. These media contain Bacto peptone, Tween 80, potassium bromide, calcium chloride, and Difco agar. Selectivity is afforded through the use of boric acid, methyl green, and the antibiotics cephalexin, 5-fluorouracil, tobramycin, and cycloheximide. Although elimination of contaminating bacteria is not total, identification of Xanthomonas is aided by the use of Tween 80, a fatty acid ester and substrate for lipolytic enzymes of the pathogen. The released fatty acids are precipitated by calcium and form soap crystals around the colonies. Also, production by Xanthomonas of a yellow pigment, a dibromomethoxyphenyl polyene, is enhanced by incorporating KBr into the media. The resulting colonies of Xanthomonas have a fried-egg appearance. Compared with King's medium B, recovery on Tween media of X. c. pv. vesicatoria averages more than 90%, as does reduction of contaminating microorganisms from soil and plant samples.

Keyword(s): Capsicum, Lycopersicon.