Diversity of Xanthomonas spp. associated with bacterial spot of processing tomatoes in Brazil

Bacterial spot has become a major problem in Brazilian processing tomato fields due to favorable environmental conditions, lack of resistant cultivars or lack of efficient chemical control. The occurrence of genetic groups/species of Xanthomonas associated with bacterial spot in tomato in Brazil was studied from 1995 to 2000, upon phenotypic and genotypic characterization of 447 strains collected in commercial fields in the Central-West and Northeast. The four recently described Xanthonionas species associated with bacterial spot of tomato were detected. The populations from the Central-West were mainly composed of X. gardneri (group D/race T2). Xanthonionas vesicatoria (group B/race T2) and X. euvesicatoria (group A/race T1) were also present in some fields but at low rates. In the Northeast, only X. euvesicatoria (group A/race T1) and X. perforans (group C/race T3) were found. Genetic variability was analysed using pulsed-field electrophoresis. Strains of X. euvesicatoria, which were collected mostly from an open pollinated variety, were more variable in contrast with those of X vesicatoria, X perforans, and X. gardneri. Further collection and characterization of 53 strains from 2002 and 2003 revealed that race T3 is already present in the Central-West associated with imported hybrid cultivars. Surveys on bacterial spot occurrence should be continuous in order to detect eventual changes in population composition.