Biological, Cultural, Genetic and Chemical Control of Pierce’s Disease
Significant progress was made on nearly all of the seven diverse objectives that comprise this long term research project. Microscopy and plant xylem chemistry studies have been initiated to understand why Xylella fastidiosa (Xf) systemically colonizes and multiplies to high concentrations in some plant hosts such as V. vinifera while only establishing “microsite” infections in other plant hosts. Field plots were established in Napa to evaluate the utility of insecticide-treated “trap” crops to reduce the numbers of blue green sharpshooter vectors that enter vineyards from adjacent riparian habitats. Experiments were conducted to better understand how cold temperatures influence the overwintering of Xf in grapevines and how severe pruning may have some promise as a management tool for PD. In vitro studies determined the concentrations of plant micronutirents such as zinc, manganese and copper that are toxic to Xf and several large field trials using these materials were established in Napa and Temecula commercial vineyards. Several methods were evaluated to introduce bactericides in grapevines. Electroporation conditions were identified that allow exogeneous DNA to be introduced into Xf cells. Numerous broad-host ranges were electroporated into Xf, however none of these vectors were stable in Xf Native Xf plasmids have been cloned, sequenced and engineered as potential shuttle vectors. Numerous crosses were made between resistant and susceptible Vitis spp. to facilitate the mapping of PD-resistance genes.