MXP, a Semi-Selective Medium forXanthomonas campestrispv.phaseoli

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Abstract
A semi-selective medium (MXP) was developed for isolation of Xanthomonas campestris pv. phaseoli and ''fuscans'' strains from common blight-infected dry beans [Phaseolus vulgaris] 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 (0.6), 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 .mu.l/L; 1% solution in 20% ethanol), and methyl green (60 .mu.l/L; 1% aqueous solution) were added before pouring the plates.