LINKING THE MODEL OF THE DEVELOPMENT OF PIERCES DISEASE IN GRAPEVINES TO AN UNDERSTANDING OF THE DYNAMICS OF GLASSY-WINGED SHARPSHOOTER TRANSMISSION OF XYLELLA FASTIDIOSA TO GRAPEVINES AND GRAPEVINE GENE EXPRESSION MARKERS OF PIERCES DISEASE

• Author(s): Backus, Elaine; Labavitch, John; Matthews, Mark; Shackel, Ken; Greve, Carl; Kirkpatrick, Bruce; Morgan, David; Perez, Alonso; Roper, Caroline;
• Abstract: For three years, our group has been testing the steps in PD development that were proposed in a model. Xf introduction to vessels>vessel cavitation> initial water deficit> Xf population increase> production of enzymes by Xf> cell wall digestion > oligosaccharide signals > ethylene synthesis rise> a "wave" of vessel occlusion beyond the infection site > collapse of vine water transport> leaf abscission>vine death In the course of that research, we have shown that xylem vessel obstruction (tyloses, plant cell wall component-derived gels, and, perhaps, bacterial extracellular polysaccharides) and consequent reductions in stem water transport capacity are early consequences of infection with Xylella fastidiosa (Xf), before bacterial populations are substantial and have spread far from the inoculation point. We have shown that ethylene treatment of vines also triggers vessel obstruction development and reduced water movement and that ethylene emanation from vines may increase following infection. We have also developed data for xylem vessel length distributions in grapevines and shown that Xf must pass through vessel pit membranes if the bacterial population is to develop systemically, thus suggesting that digestion of cell wall polymers in the pit membranes is likely to be important to disease spread. These findings are reported in several reports at the annual PD Symposium and, more recently, at disciplinary scientific society meetings and in refereed reports (Stevenson et al., 2004). Work to retest aspects of our model, those parts relating specifically to the involvement of cell wall breakdown caused by the action of Xf enzymes, remain and will be tested in this new proposal (see Objectives). Also to be tested are ideas based on the reports of the studies of others involved in unraveling problems associated with the transmission and spread of PD, within and between grapevines. We will link the anatomical, biochemical and physiological findings from our model testing to the work of Cook et al. (), describing genes that are expressed in vines relatively soon after Xf infection. We have nothing to report on this aspect of the new proposal. We will also address a question that entomologists and plant biologists generally have differing opinions about. Do vessels cavitate (i.e., become air-filled and, hence, non-functional when the glassy-winged sharpshooter (GWSS) starts or finishes its feeding on a vine? The answer to this question may have important implications regarding Xf transmission, GWSS feeding strategy and spread of the bacteria in an infected vine. Below and in the report from Shackel and Labavitch in these proceedings, we report on the start we have made in addressing this question.
• Publication Date: Dec 2004
• Journal: 2004 Pierce's Disease Research Symposium