PILUS-MEDIATED ADSORPTION OF PSEUDOMONAS-SYRINGAE TO THE SURFACE OF HOST AND NONHOST PLANT-LEAVES

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 phi6. Phage-r esistant 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 no n-host plants. Scanning electron microscopy of the P. syringae pathova r syringae strain R32 and the pathovar phaseolicola strain HB10Y revea led a difference between these strains in the distribution of the bact erial cells over the lower bean leaf surface. P. syringae pv. syringae spread evenly over the leaf surface whereas P. syringae pv. phaseolic ola adsorbed preferentially to the stomata. No such localization was o bserved on chloroform-treated leaves, where the cells of both pathovar s were evenly distributed. Adsorption of bacteria to leaf disks was in dependent of divalent cations, and no specific ionic conditions were r equired.