Characterization of strains of Xanthomonas campestris pv campestris from organic farming systems and reaction of brassicas to black rot

Ninety strains of Xanthomonas campestris pv. campestris (Xcc) from brassicas grown tinder organic farming systems in the 'Mata' and 'Agreste' regions of Pernambuco, Brazil, were characterized based upon sensitivity to antibiotics and copper sulfate, and esterase activity. Most of the strains showed high sensitivity to tetracycline (76.6%), erythromycin (63.3%) and streptomycin (63.3%), resistance to amoxicilin (70%), gentamicin (40.0%) and norfloxacin (45.5%) and medium sensitivity (44.4%) or resistance (44.4%) to neomycin. Fifty-five strains of Xcc were resistant to copper Sulfate at 50 mg mL(-1) and all of them to 200 mg mL(-1); 92.22% of the strains showed esterase activity. Strains were grouped in seven similarity groups by the Euclidean analysis-single linkage. The reaction of 14 genotypes of brassicas to strain 'B21' of Xcc was also studied. The genotypes significantly differed among them in relation to incubation period, incidence and disease severity. The highest disease severity was recorded on broccoli 'Ramoso', cauliflower 'Bola de Neve' and 'Piracicaba de Verao', and cabbage 'Chato de Quintal', classified as highly susceptible to black rot. The Chinese cabbage hybrids 'AF 70', 'AF 72', 'AF 69' and 'AF 66' were highly resistant to black-rot, while broccolis 'Ramoso' and 'Piracicaba Precoce', cauliflower 'Piracicaba de Verao' and 'Hibrido Cindy' and cabbage '60 Dias' showed intermediate resistance.