Diversity of Xanthomonas campestris pv vesicatoria in tomato and pepper fields of Mexico

Analysis of 101 strains of Xanthomonas campestris pv. vesicatoria from tomato and pepper fields of the Sinaloa and Sonora regions of Mexico revealed that 95% were X. c. vesicatoria group A and the remaining 5% were group C. In 1992, all strains isolated from fields in Sinaloa belonged to group A, whereas a new strain type, genetically related to the A group but strongly amylolytic, was isolated from fields in Sonora. In 1993, only typical A strains were isolated from fields in sonora, whereas, amylolytic A strains were isolated from pepper plants grown in Culiacan, Sinaloa. Also in 1993, group C strains were isolated from tomato plants in two fields in Guasave, Sinaloa; these were determined to be race T3. This is the first isolation of C strains from a production field outside the United States. Another uncommon strain present in the region was pepper race PO; this race was prevalent in Sinaloa. The distribution of the races in western Mexico varied from year to year and field to field. Most strains were resistant to both copper and streptomycin; thus, it appears that these bactericides will not be useful in controlling the disease in the region.