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.