Brazil and USA are the major orange juice producing countries in the world. In both countries, orange orchards are attacked by several diseases that cause severe losses to the citrus industry. Among the most serious diseases is citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac), a phytopathogenic bacteria whose genome was completed sequenced in 2002 (Silva et al.). This created the perspective of a more effective control of the disease, through the use of new strategies as functional genome analysis.  In our laboratory, a bank of 3,300 Xac mutants were obtained by random insertion of transposon sequence (EZ:TN Kit; Epicentre). The pathogenicity of these mutants were tested by individual inoculated in Citrus limonia seedlings and 100 were selected based on the different symptoms they induced in infected plants when compared to Xac wild type (wt). For each mutant the truncated gene was confirmed by sequencing. Through growth curves in vitro and in planta we evaluate the growth profile of 16 mutants.  The in vitro growth curves allowed us to identify the mutants whose growth profile were similar to that observed for Xac wt.  The in planta growth curves enabled us to identify the mutants whose growth profile in the plant were different from the observed for the wt bacterium.  Mutants with reduction in the multiplication capacity inside the plant host, but that present a similar development  to wt bacterium in vitro, may correspond to mutants whose knocked out genes can be related to characteristics of pathogenicity and virulence in Xac.  The qualitative and quantitative characteristics and functions of the putative pathogenicity/virulence related genes will be presented.