AN AGAR MEDIUM FOR THE ISOLATION AND IDENTIFICATION OF XANTHOMONAS-CAMPESTRIS PV VESICATORIA FROM SEED

An agar medium was developed for the isolation and identification of Xanthomonas campestris pv. vesicatoria, the causal agent of bacterial spot of pepper and tomato. The new medium, designated as CKTM, contained soy peptone, Bacto tryptone, dextrose, L-glutamine, L-histidine, ammonium phosphate, potassium phosphate, magnesium sulfate, calcium chloride, Pourite, and agar. Selectivity was afforded with cycloheximide, bacitracin, neomycin, cephalexin, 5-fluorouracil, tobramycin, and Tween 80. Strains of X. c. vesicatoria were easily distinguished from strains of other pathovars of X. campestris by the formation of a clear ring around their colonies. The ring appeared 1-2 days after colony transfer or 3-4 days after serial dilutions were plated. Minute tan to white crystals of various intensity formed in the clear ring. X. c. vesicatoria was detected in 15 of 22 seed lots. Recovery of X. c. vesicatoria from tomato seed ranged from 17.7 to 100% on CKTM compared with 6.3 to 44.4% on Tween B medium. In addition, recovery of X. c. vesicatoria on CKTM medium was qualitatively superior to that of Tween B medium, with a greater reduction of contaminating microflora.