BIOLOGICAL, CULTURAL, GENETIC, AND CHEMICAL CONTROL OF PIERCE'S DISEASE: SIGNIFICANCE OF RIPARIAN PLANTS IN THE EPIDEMIOLOGY OF PIERCES DISEASE

• Author(s): Baumgartner, Kendra; Purcell, Alexander; Walker, Andrew;
• Abstract: The goal of this research is to evaluate the significance of riparian hosts in the epidemiology of Pierces disease (PD) in the North Coast grape-growing region of California. Our first objective is to examine the epidemiological role of seasonal Xylella fastidiosa (Xf) concentration fluctuations in riparian hosts in the field, where plants are subject to seasonal temperature changes. Among systemic riparian hosts, differences in seasonal Xf concentrations and Graphocephala atropunctata (blue-green sharpshooter, BGSS) feeding preference affect their importance as Xf reservoirs. Temperature affects Xf concentrations in plant hosts and, in turn, Xf concentrations affect the probability of a BGSS acquiring Xf while feeding on an infected plant. We focused on Xf concentrations in five systemic hosts: Rubus discolor (Himalayan blackberry), R. ursinus (California blackberry), Sambucus mexicana (blue elderberry), Vinca major (periwinkle), and Vitis californica (California grapevine). We needle inoculated potted plants of California grape, California blackberry, Himalayan blackberry, blue elderberry, and periwinkle in the greenhouse. After confirming infection with PCR, we transferred infected plants to two sites in the North Coast (Napa County and Mendocino County). Populations of Xf reached detectable levels in all five riparian hosts located at our Napa County site in October 2003. Every replicate plant of periwinkle and California grapevine showed typical leaf scorch symptoms of PD, which is not surprising given the high concentrations of Xf detected among them. The fact that none of the Himalayan blackberry showed symptoms, despite high Xf concentrations, suggests that Himalayan blackberry is more tolerant of Xf infection. Assuming our results reflect that of naturally-established riparian hosts in the field, Xf concentrations in California grapevine, Himalayan blackberry, and periwinkle are still sufficient for acquisition by BGSS in autumn. Dilution plating results have not yet been obtained from our Mendocino County site and real-time PCR reactions have not been completed for plants from either site. We will continue to estimate Xf concentrations in plants at both sites using dilution plating and real-time PCR on a seasonal basis. Xf concentration estimates from each plant species at each site will be averaged among replicate plants. The effects of plant species, season, and location on mean Xf concentration will be determined using an analysis of variance. Results obtained using the two quantitation techniques will be analyzed separately.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium