According to results significant differences were found in the effect of antibiotics on growth of Xoo isolates. Duncan multiple range test revealed 5 distinct groups. Fitt et al. (1992) reported that some antibiotics can control bacterial growth when these were daily applied to the culture media; according to the observation chloramphenicol and penicillin/ dihydrostreptomycin were effective only during the first 48 h, despite continuous replacement with fresh antibiotics.