Rickettsia-like Bacterium Associated with Pierce's Disease of Grapes.

A pleomorphic bacterium was observed by electron microscopy in grape plants infected with Pierce's disease. The organism was located in xylem tissue, and its occurrence was closely associated with symptoms of Pierce's disease. The bacterium resembled a rickettsia in morphology, in its failure to grow on cell-free media, and in its sensitivity to tetracycline antibiotics.