Alternative Hosts of Pierce'S Disease of Grapevines that Occur Adjacent to Grape Growing Areas in California

Abstract

Wild plants were collected in and around vineyards along the Napa River in California. Leaf and stem samples were tested by enzyme-linked immunosorbent assay (ELISA) for Pierce's disease bacterium. Positive reactions were obtained for Paspalum dilatatum, Conium maculatum, and Cyperus eragrostis collected from areas with high Pierce's disease incidence in the adjacent grapevines. No positive reaction was obtained with any plant from areas without Pierce's disease in nearby grapevines. Electron microscopy or light microscopy detected bacteria with rippled cell walls in infected P. dilatatum and C. maculatum. A gram-negative catalase-positive bacterium was isolated from P. dilatatum collected along the Napa River but not from others that were ELISA-negative. When infected and uninfected plants of P. dilatatum were transferred and held in pots in the greenhouse, the infected ones became stunted and fruitless, in contrast to uninfected plants, which developed into fruit-bearing plants about 60 dm tall. The bacteria isolated from P. dilatatum (PS-NA-1) are serologically the same as Pierce's disease bacterium isolated from grapes. The bacteria from Paspalum produced typical Pierce's disease symptoms in Mission grapes that were inoculated by needle injection but not in uninoculated ones. The same bacterium was isolated from the symptomatic grape leaves.