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Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings Publication Acceptance Date: 11/4/2003 Publication Date: 12/8/2003 Citation: Baumgartner, K. 2003. Significance of seasonal fluctuations of xylella fastidiosa concentrations in riparian plants in the epidemiology of pierce's disease. CDFA Pierce's Disease Control Program Research Symposium. Interpretive Summary: The objective of this research is to determine how riparian plants that host the Pierce's Disease (PD) pathogen, Xylella fastidiosa (Xf), contribute to the spread of PD. Our first objective is to measure seasonal Xylella fastidiosa (Xf) concentration fluctuations in riparian hosts. Among riparian hosts, differences in seasonal Xf concentrations and insect vector 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 vector acquiring Xf while feeding on an infected plant. We focused on five riparian hosts: Rubus discolor (Himalayan blackberry), R. ursinus (California blackberry), Sambucus mexicana (blue elderberry), Vinca major (periwinkle), and Vitis californica (California grapevine). Potted plants of California grape, California blackberry, Himalayan blackberry, blue elderberry, and periwinkle were inoculated with Xf in the greenhouse. Infected plants were transferred to two sites (Napa, Mendocino). Xf populations reached detectable levels in all five riparian hosts in Napa in October 2003. Every periwinkle and California grapevine plant 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 these results reflect what occurs in 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. Technical Abstract: The goal of this research is to evaluate the significance of riparian hosts in the epidemiology of Pierce's Disease (PD) in North Coastal California. Our first objective is to examine the epidemiological role of seasonal Xylella fastidiosa (Xf) concentration fluctuations in riparian hosts. 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 five riparian hosts: Rubus discolor (Himalayan blackberry), R. ursinus (California blackberry), Sambucus mexicana (blue elderberry), Vinca major (periwinkle), and Vitis californica (California grapevine). Potted plants of California grape, California blackberry, Himalayan blackberry, blue elderberry, and periwinkle were needle-inoculated in the greenhouse. After confirming infection with PCR, infected plants were transferred to two sites (Napa, Mendocino). Xf populations reached detectable levels in all five riparian hosts in Napa 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 these 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. |
