JWSS - Journal of Water and Soil Science

Pseudomonas syringae is a phytopathogenic bacterium with a wide host range. The biology of this bacterium consists of two phases. The first phase is the indication of disease on the host plant which generally appears in the form of necrosis on the aerial parts of plant (pathogenicity phase). The second phase is a rapid multiplication of bacteria on the aerial surface of the plant without inflicting any defense response (epiphytic phase). In this study, the impact of pathogenic virulence genes of aggress, dsp, ice, cor and hrp genes in the epiphytic process of Pseudomonas syringae on resistant and sensitive varieties of tomato is examined. The population dynamism of bacterial colonization on the root, stem and leaves was studied.

The results indicated that the hrp genes system (hypersensitive reaction and pathogenicity) in Pseudomonas syringae pv. tomato, P. s. pv. syringae and P. s. pv. phaseolicola and the coronatine gene system in P. s. pv. tomato are necessary for colonization on both host and non-host plants. The mutants isolates of hrp and cor compared with wild isolates could colonize at a lower level on all parts of the plant. In contrast, the ice (Ice nucleation), aggress (Agressivity) and dsp (disease specific) gene systems had no significant impact on the epiphytic colonization of P. s. pv. syringae. However, under in vitro conditions no significant difference was observed among the wild type isolates and their mutants in king B medium in the bioscreen machine. It is concluded that the lower multiplication of P. syringae mutants in planta is due to the plant-bacteria interaction.