IDENTIFICATION OF MECHANISMS MEDIATING COLD THERAPY OF XYLELLA FASTIDIOSA- INFECTED GRAPEVINES

• Author(s): Kirkpatrick, Bruce; Meyer, Melody;
• Abstract: During October/November 2004, 11 control and 11 Xylella fastidiosa (Xf) infected Pinot Noir and Cabernet Sauvignon grapevines grown in five gallon pots were transported to four locations in Northern California with different winter severities. Another set of similar healthy and Xf-infected vines were placed in four different cold rooms with varying temperatures. These vines were rated for mortality and remission of Pierces disease (PD) symptoms in fall 2005. A high level of mortality occurred at the coldest location (Fall River, Shasta County), moderate mortality occurred at UC Blodgett Research Station, while little mortality occurred at the UC Davis and Hopland sites. Disease ratings were lower in vines from the three cold temperature sites compared to vines grown at UC Davis, however the large discrepancy in the number of vines surviving at each location prevented meaningful comparisons between the field sites. Unexpectedly, mortality of vines in the warmest and coldest chamber regimes was greater than the two intermediate temperatures. Disease severity was also greatest in the warmest temperature which may have contributed to the observed high mortality when the vines were subsequently planted in the field. All three cold chamber regimes had lower disease ratings than the warmest temperature. Comparisons of xylem sap pH and osmolarity in Cabernet vines growing in a vineyard in Placer County and UC Davis were not consistent with results obtained in 2004. Differences in the date of collection may have influenced these results. Effects of buffer and xylem sap on the survival of Xf and various cold temperatures were reported in the Proceedings of the 2004 Pierces Disease Research Symposium. Abscisic acid (ABA) levels are elevated in many cold-treated plants and ABA has been shown to induce the synthesis of certain pathogenesis related (PR) proteins that in some case possess anti-fungal properties. ABA concentrations were lower in xylem sap collected from vines growing in El Dorado County compared to UC Davis, which suggests ABA is probably not directly mediating the cold therapy phenomenon. However, we are proceeding with experiments to determine if exogenous applications of ABA on non-chilled grapevines can elicit PR proteins.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium