Infection Sites of Pseudomonas cichorii into Head Leaf of Lettuce

Abstract

Sections of middle head leaf of lettuce were stained with fluorescein isothiocyanate-conjugated antibody against Pseudomonas cichorii, a causal agent of bacterial rot of lettuce, and were observed under a fluorescent microscope. Fluorescent antibody-labeled P. cichorii cells were observed in stomata of the sections, which did not contain browing symptom of the disease. Special fluorescent specks derived from P. cichorii were most frequently observed in guard cells and intercellular spaces of substomatal cavities. Browing, which was the initial symptom of disease, progressed from epidermis to mesophyll. In advance of progress of browing symptom, specific fluorescent specks were observed in intercellular spaces of epidermis and then were observed in intercellular spaces of mesophyll. These results suggested that P. cichorii first invaded head leaf of lettuce through stomata, later multiplied in intercellular spaces of epidermis and colonized intercellular spaces of mesophyll. Specific fluorescent specks were also observed in leaf hairs.