Pseudomonas syringae is multi host generalist pathogen, it can infect more than 100 families plants. It has a complex life history, including pathogenic, epiphytic and saprophytic phases. The mechanisms of pathogen virulence and host resistance have been well characterized in several model systems. But knowledge about genetic dynamics in ecology is limited. Tn-seq high-throughput parallel sequencing will be used to elucidate the fitness mechanism of Pseudomonas syringae in crops.