The production of citrus fruits is one of the most important agro-industrial activities in our country, which comes being constantly threatened to the citric canker disease, caused by the gram negative bacterium Xanthomonas axonopodis pv. citri (Xac-A). This bacterium when in contact with host plants provokes injuries to leaves, fruits and branches.  On the other hand, when this pathogen infects a non-host plant a necrotic reaction is induced. The diverse mechanisms of plant defense to pathogen attack include those mediated by genes coding for the production of ethylene, salicylic acid, jasmonic acid, fhytoalexin, PR proteins and reactive species of oxygen (ROS).  In this work we have been investigating the expression of resistance response genes during Xanthomonas axonopodis pv. aurantifoli C (Xaa-C)::citrus (resistance response) and the behavior of gene expression during Xac-A::citrus interaction/(citrus canker-illness). Bacterial suspensions (Xac-A or Xaa-C) were inoculated to orange leaves (Citrus sinensis), which were then collected during a bacterial kinetic of infection. The expression of genes related to plant resistance responses have been analyzed by Northern blot with the aid of specific plant probes corresponding to PCR sequences coding to representatives of the resistance metabolic pathways cited above, amplified from orange leaves genomic DNA. The Xaa-C::citrus interaction has shown to induce a more rapid and intense expression of plant resistance pathways when compared to Xac-A::citrus interaction. The plant resistance pathways affected by disease inducing Xac-A::citrus interaction will be discussed.