Fate of Pierce's disease strains of Xylella fastidiosa in common riparian plants in California

The fate of strains of the bacterium Xylella fastidiosa that cause Pierce's disease of grapevines was investigated in 33 species of mostly perennial p lants common in riparian habitats in northern coastal California grape-grow ing regions. Plants were inoculated in the field with needle puncture using cultured cells of X, fastidiosa as inoculum or inoculated in the laborator y with infective insect vectors (Graphocephala atropunctata). Populations o f X. fastidiosa were highest in most plant species within 3 to 6 weeks of i noculation, followed by declines in populations of viable bacteria over the next 3 to 4 months. Homogenates of petioles of California black walnut (Ju glans hindsii) and coffeeberry (Rhamnus californica) inhibited in vitro gro wth of X. fastidiosa, precluding culture of the bacterium from these plants . Big leaf maple (Acer macrophyllum), California buckeye (Aesculus californ ica), California blackberry (Rubus ursinus), coast live oak (Quercus agrifo lia), elderberry (Sambucus mexicana), French broom (Genista monspessulanus) , periwinkle (Vinca major), valley oak (Quercus lobata), and the grape root stock Vitis rupestris supported systemic populations of X, fastidiosa that survived throughout the year outdoors in Napa Valley, California.