Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/6/2005
Publication Date: 12/5/2005
Citation: Labavitch, J., Backus, E.A., Matthews, M., Shackel, K. 2005. Linking the model of the development of Pierce's Disease in grapevines to an understanding of the dynamics of gwss transmission of xylella fastidiosa to grapevines and grapevine gene expression markers of Pierce's Disease. Proceedings of the 2005 Pierce's Disease Symposium. p.34-38.
Interpretive Summary: We showed that polygalacturonase (PG), an enzyme produced by Xylella fastidiosa (Xf) actually contributes to development of Pierce’s Disease symptoms in inoculated grapevines. In particular, the size of vessel pores increases with Xf infection, presumably allowing bacterial cells to pass from vessel to vessel, and thus to spread to new tissues to eventually kill the plant. When Xf-derived PG and endoglucanase are together artificially introduced into grapevine stems, the same increase in porosity occurred. In addition, work was begun to determine whether feeding of glassy-winged sharpshooters (GWSS) causes cavitation of xylem vessels. Insect colonies and host plants were reared, and numerous protocols for recording simultaneous insect feeding and vessel cavitation were developed.
Technical Abstract: This project is testing various steps in a model of Pierce’s Disease etiology that proposes that introduction of Xylella fastidiosa (Xf) into grapevine xylem vessels leads to cavitation, subsequent water deficit, then population growth of the Xf, subsequent production of enzymes by Xf, leading to cell wall digestion, oligosaccharide signal release and ethylene synthesis. Research this year emphasized testing the production of enzymes by Xf and later steps in the model. Successes include the demonstration that the putative Xf polygalacturonase (PG) gene actually encodes a PG, and the fact that this PG contributes to symptom development in inoculated grapevines. In particular, it was found that vessel porosity increases with Xf infection, and that when Xf-derived PG and endoglucanase are together artificially introduced into grapevine stems, the same increase in porosity is observed. In addition, work was initiated to determine whether feeding of glassy-winged sharpshooters (GWSS) causes cavitation of xylem vessels. Insect colonies and host plants were reared; protocols were developed for simultaneous recording of GWSS feeding via electrical penetration graph monitoring and cavitation via electrical acoustic monitoring. Also, imaging of air-filled vs. water-filled vessels in grape was accomplished via MRI. All of these methods will be put together in the coming year.