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MXP, a Semi-Selective Medium for Xanthomonas campestris pv. phaseoli. L. E. Claflin, Department of Plant Pathology, Kansas State University, Manhattan 66506; A. K. Vidaver(2), and M. Sasser(3). (2)Department of Plant Pathology, University of Nebraska, Lincoln 68583; (3)Department of Plant Science, University of Delaware, Newark 19711. Phytopathology 77:730-734. Accepted for publication 24 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-730.

A semi-selective medium (MXP) was developed for isolation of Xanthomonas campestris pv. phaseoli and ‘fuscans’ strains from common blight-infected dry beans and infested soil. All X. c. pv. phaseoli strains tested grew on MXP and most X. campestris pathovars tested grew equally well. Other phytobacterial pathogens of bean failed to produce colonies on MXP. For recovery from seed, incubation for 6 hr at 28 C in a diluent of 12.5 mM PO₄ + 10 mM MgSO₄ + 0.01% Tween 20 resulted in the greatest number of cells of X. c. pv. phaseoli recovered. Incubating seeds in distilled water resulted in limited or no recovery of X. c. pv. phaseoli. MXP medium consists of (in grams per liter): K₂HPO₄ (0.8), KH₂PO₄ (0.6), yeast extract (0.7), soluble potato starch (8.0), potassium bromide (10.0), glucose (1.0), and agar (15.0). After autoclaving, chlorothalonil (15 mg/L), cephalexin (20 mg/L), kasugamycin (20 mg/L), gentamycin (2 mg/L), methyl violet 2B (30 μl/L; 1% solution in 20% ethanol), and methyl green (60 μl/L; 1% aqueous solution) were added before pouring the plates.