Distribution of 66 type III effector (T3E) genes among 55 strains of Xanthomonas citri pv. citri and Xanthomonas citri pv. bilvae. Presence or absence of an orthologue of each selected T3E was determined by polymerase chain reaction (PCR) and Southern blot when necessary. Black, grey and white squares represent the presence, interruption by an insertion sequence and absence, respectively