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 Pierce9s disease bacterium. Positive reactions were obtained for <i>Paspalum dilatatum, Conium maculatum</i>, and <i>Cyperus eragrostis</i> collected from areas with high Pierce9s disease incidence in the adjacent grapevines. No positive reaction was obtained with any plant from areas without Pierce9s disease in nearby grapevines. Electron microscopy or light microscopy detected bacteria with rippled cell walls in infected <i>P. dilatatum</i> and <i>C. maculatum</i>. A gram-negative catalase-positive bacterium was isolated from <i>P. dilatatum</i> collected along the Napa River but not from others that were ELISA-negative. When infected and uninfected plants of <i>P. dilatatum</i> 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 <i>P. dilatatum</i> (PS-NA-1) are serologically the same as Pierce9s disease bacterium isolated from grapes. The bacteria from <i>Paspalum</i> produced typical Pierce9s 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.