SCANNING ELECTRON-MICROSCOPY OF OLIVE AND OLEANDER LEAVES COLONIZED BY PSEUDOMONAS-SYRINGAE SUBSP SAVASTANOI

Leaves of olive and oleander were sprayed with suspensions of their homologous strains (PVBa230 and ITM519, respectively) of Pseudomonas syringae subsp. savastanoi and examined by SEM. It was found that both strains multiplied on the lower surface of the leaves of both species. Preferred sites for survival and multiplication were the shields of peltate hairs on olive and the stomatal pits on oleander. The findings suggest that, at least in olive leaves, some bacteria entered the leaf tissue through the stomata but that this was not important since cells which entered the host did not cause any disease symptoms. Cells of both strains were agglomerated and cells of ITM519 were further attached to the surface of the leaf hairs on oleander by fibrillar material. Inoculated leaves did not show any disease symptoms except at leaf abscission scars on olive plants where leaves had been excised prior to inoculation. It is suggested that on both olive and oleander preexisting wounds are necessary for symptoms to develop.