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Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings Publication Acceptance Date: 11/2/2002 Publication Date: 12/16/2002 Citation: Baumgartner, K. 2002. Significance of 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. A preliminary experiment was initiated at three commercial vineyards in Napa County, CA, to measure seasonal Xf populations in five riparian host species: Vitis californica (California grape), Rubus ursinus (California blackberry), Rubus discolor (Himalayan blackberry), Sambucus mexicana (blue elderberry), and Vinca major (periwinkle). All five species are known hosts of Xf and the vector of PD in North-coastal California, Graphocephala atropunctata (blue-green sharpshooter, BGSS). In spring, plants of five riparian host species were inoculated with Xf by placing a drop of a suspension of cultured Xf cells on a stem and piercing the stem with a pin beneath the suspension. In summer, fall, and winter following inoculation, Xf populations were estimated in inoculated plants. Populations of Xf reached detectable levels in California blackberry, blue elderberry, and California grape in summer and increased fall. Xf was not detected in periwinkle until early fall, when populations were found to be as high as that of California blackberry, blue elderberry, and California grape. Due to low inoculation success, the number of plants that developed infections was too low to obtain an adequate sample size for statistical analysis of Xf concentrations among riparian hosts and seasons. Methodology has been modified to improve inoculation success by inoculating riparian host plants propagated in the greenhouse, instead of relying on naturally-established plants in the field, and reducing the rate of contamination on culture plates. Technical Abstract: The objective of this research is to determine the epidemiological role of riparian hosts in the spread of Pierce's Disease (PD). A preliminary experiment was initiated at three commercial vineyards in Napa County, CA, to measure seasonal Xf populations in five riparian host species: Vitis californica (California grape), Rubus ursinus (California blackberry), Rubus discolor (Himalayan blackberry), Sambucus mexicana (blue elderberry), and Vinca major (periwinkle). All five species are known hosts of Xf and Graphocephala atropunctata (blue-green sharpshooter, BGSS), the most efficient vector of PD in North-coastal California. In spring, individuals of the five riparian host species were inoculated with a PD strain of Xf by placing a drop of a suspension of cultured Xf cells on a stem and piercing the stem with a pin beneath the suspension. In summer, fall, and winter following inoculation, Xf populations were estimated in petioles located immediately distal to stem inoculation sites by dilution plating. Populations of Xf reached detectable levels in California blackberry, blue elderberry, and California grape in summer and increased fall. Xf was not detected in periwinkle until early fall, when populations were found to be as high as that of California blackberry, blue elderberry, and California grape. Due to low inoculation success, the number of plants that developed infections was too low to obtain an adequate sample size for statistical analysis of Xf concentrations among riparian hosts and seasons. Methodology has been modified to improve inoculation success by inoculating riparian host plants propagated in the greenhouse, instead of relying on naturally-established plants in the field, and reducing the rate of contamination on culture plates. |
