Pilus-mediated adsorption of Pseudomonas syringae to the surface of host and non-host plant leaves

SUMMARY: Adsorption of cells of a variety of Pseudomonas syringae pathovars to the leaf surface of host and non-host plants was measured. The strains used were sensitive to the pilus-specific bacteriophage ø6. Phage-resistant non-piliated mutants were isolated and found to have reduced ability to adsorb to plant surfaces. The pilus-mediated adsorption was not host-specific. Piliated strains adsorbed well to both host and non-host plants. Scanning electron microscopy of the P. syringae pathovar syringae strain R32 and the pathovar phaseolicola strain HB10Y revealed a difference between these strains in the distribution of the bacterial cells over the lower bean leaf surface. P. syringae pv. syringae spread evenly over the leaf surface whereas P. syringae pv. phaseolicola adsorbed preferentially to the stomata. No such localization was observed on chloroform-treated leaves, where the cells of both pathovars were evenly distributed. Adsorption of bacteria to leaf disks was independent of divalent cations, and no specific ionic conditions were required.