ARS | Publication request: The Egestion-Salivation Hypothesis: Evidence for the role of vector saliva in the inoculation mechanism of Xylella fastidiosa

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 3, 2010
Publication Date: June 1, 2010
Citation: Backus, E.A., Andrews, K., Labavitch, J., Greve, L. 2010. The Egestion-Salivation Hypothesis: Evidence for the role of vector saliva in the inoculation mechanism of Xylella fastidiosa. Phytopathology. 100(6):S9-S10.

Technical Abstract: Despite ca. 40 years of study, the mechanism of inoculation of the Pierce’s Disease bacterium, Xylella fastidiosa (Xf), by vectors such as the glassy-winged sharpshooter (GWSS) is still unknown. Research on the Egestion-Salivation Hypothesis for Xf inoculation will be presented. Two important steps in this hypothesis are uptake of saliva containing the cell wall-degrading enzyme beta-1,4 glucanase into the precibarium where Xf colonies develop, followed by injection of this enzyme-containing saliva into the xylem prior to ingestion. To directly test the role of saliva in inoculation, immunohistology was used to study interactions between Xf and GWSS saliva in grapevine. Adult GWSS were confined in small cages on grapevine stems for 24 hours and allowed to probe, leaving salivary deposits in the plant. Xf was then needle-inoculated into the same stem area; 1 hour later, the tissue was excised and prepared for immunohistology using a commercial Xf probe. Xf bacteria observed in xylem cells penetrated the semi-viscous saliva deposited during GWSS probing prior to Xf inoculation. Therefore, Xf bacteria have the ability to infiltrate gelled saliva containing salivary glucanase. This suggests that, in a natural GWSS inoculation, Xf could potentially migrate out of injected saliva and into xylem fluid. Implications for the mechanism of inoculation are discussed.