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A New Semiselective Medium for the Isolation of Xanthomonas campestris pv. campestris from Crucifer Seeds. C. J. Chang, Department of Plant Pathology, University of Georgia, Georgia Station, Griffin, 30223-1797; R. Donaldson(2), M. Crowley(3), and D. Pinnow(4). (2)Department of Plant Pathology, University of Georgia, Georgia Station, Griffin, 30223-1797; (3)(4)Seed Laboratory, Georgia State Department of Agriculture, Griffin, 30223-1797. Phytopathology 81:449-453. Accepted for publication 19 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-449.

Antibiotics were evaluated for inclusion in a semiselective medium for isolation of Xanthomonas campestris pv. campestris from crucifer seed. Ampicillin, penicillin G, and tetracycline completely inhibited the growth of X. c. campestris B-24 at 6.25 ?g/ml or less, whereas carbenicillin, cephalothin, gentamicin, and kanamycin inhibited X. c. campestris at 25–80 ?g/ml. Bacitracin, neomycin, and streptomycin were least inhibitory with the minimal inhibitory concentrations at >400, 160, and 640 ?g/ml, respectively. CS20ABN medium was developed by incorporation of bacitracin, neomycin, and cycloheximide at 100, 40, and 100 ?g/ml, respectively, into CS20A. Washings from samples of crucifer seed were assayed for X. c. campestris on five media: CS20A, CS20ABN, NSCA, NSCAA, and FS. Saprophytic bacteria were often too numerous to count and overgrew X. c. campestris on all media except CS20ABN where 59–100% of recovered colonies were X. c. campestris. Colony size of X. c. campestris on CS20ABN was two- to threefold or three- to sevenfold larger than that on NSCA and NSCAA or FS, respectively.