Abstract
The interaction between a bacterial pathogen and its potential plant host develops from a complex combination of bacterial and plant elements, which determines either the establishment of resistance or the development of disease. The use of virulence assays based on competitive index in mixed infections constitutes a powerful tool for the analysis of bacterial virulence factors. In this work, we describe how the use of competitive index assays also constitutes an alternative approach for the analysis of plant immunity, to determine the contribution of different elements to bacterial recognition or immunity signaling.