VIRULENCE ANALYSIS OF THE PIERCES DISEASE AGENT XYLELLA FASTIDIOSA

• Author(s): Bruening, George; Civerolo, Ed; Gilchrist, David; Kirkpatrick, Bruce;
• Abstract: The glassy-winged sharpshooter, Homolodisca coagulata, spreads the causative agent of Pierces disease, the bacterium Xylella fastidiosa (Xf). Depending on whether the glassy-winged sharpshooter can establish itself in Northern California, Pierces disease may represent a multi-billion dollar threat to the grape and wine industry and the associated tourist trade. The symptoms of Pierces disease include a yellowing and gradual necrosis (scorching) of grapevine leaf edges, stunting of cane growth, and, particularly in the spring for vines infected for two or more seasons, inter-veinal chlorosis of leaves (Hewitt, 1970). (Lee et al., 1982) reported that detached grape leaves from grape cultivars that are particularly sensitive to Pierces disease, showed typical marginal yellowing and scorching in less that 12 hr after petiole uptake of cell-free washing from Xf cells grown on agar plates. The activity did not survive autoclaving or multiple freezing and thawing and was not inactivated by incubation with proteinase K. No activity was observed for washings of uninoculated agar plates. Applying the conditions of (Lee et al., 1982), (Goodwin et al., 1988) also observed phytotoxicity after petiole uptake of cell-free washing, but from both Xf-populated and uninoculated agar plates. Further, (Goodwin et al., 1988) found a correlation between increased midday stomatal resistance and symptom development on leaf margins and an approximately six-fold increase in leaf proline content (fresh-weight basis) associated with Pierces disease. They discounted phytotoxins as significant contributors to Pierces disease symptoms and state that The biophysical and biochemical changes observed for diseased vines indicate that marginal leaf necrosis occurs when water stress develops. Diseased leaves are apparently water stressed because of vascular dysfunction which, when prolonged, may result in accelerated leaf senescence. (Goodwin et al., 1988) also found that higher stomatal resistance was associated with spring inter-veinal chlorosis but was not as pronounced as the stomatal resistance increase observed for leaves showing symptoms first at the margin.
• Publication Date: Dec 2001
• Journal: 2001 Pierce's Disease Research Symposium