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Title:   Author  item
                                            Baumgartner, Kendra
  Submitted to: CDFA Pierce's Disease Control Program Research Symposium
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 11/1/2004
                                    Publication  Date: 12/7/2004
                                    Citation: Baumgartner, K. 2004. Significance of riparian plants in the epidemiology of pierce's disease. CDFA Pierce's Disease Control Program Research Symposium.Interpretive Summary: The goal of this research is to determine how riparian hosts contribute to the spread of Pierce's Disease (PD) in the North Coast grape-growing region of California.  The first objective is to examine seasonal changes in concentrations of the pathogen, Xylella fastidiosa (Xf) in riparian hosts.  Changes in pathogen concentrations affects transmission of PD from riparian hosts to grapevines by the insect vector, Graphocephala atropunctata (blue-green sharpshooter, BGSS).  As temperatures increase, Xf concentrations increase, which, increases the probability of disease transmission.  We focused on five riparian hosts: Himalayan blackberry, California blackberry, blue elderberry, periwinkle, and California grapevine.  We inoculated potted plants of each species in the greenhouse and transferred all infected plants to two sites in the North Coast (Napa County, Mendocino County).  Xf was not detected in the majority of plants after several months in the field (from July to Oct. 2003), except for periwinkle which maintained a high number of infected plants through all seasons.  Xf concentrations were highest in periwinkle in all seasons and at both sites, and were sufficient for BGSS transmission year-round.  California grape and Himalayan blackberry supported Xf concentrations that were sufficient for BGSS transmission in autumn and summer, but not in spring.  These results suggest that BGSS likely acquires Xf from riparian hosts in autumn, instead of spring.
                                Technical Abstract: The goal of this research is to evaluate the significance of riparian hosts in the epidemiology of Pierce's Disease (PD) in the North Coast grape-growing region of California.  The first objective is to examine the epidemiological role of seasonal changes in Xylella fastidiosa (Xf) concentrations 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 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 and transferred all infected plants to two sites in the North Coast (Napa County, Mendocino County).  Xf was not detected in the majority of plants after several months in the field (from July to Oct. 2003), except for periwinkle which maintained a high number of infected plants through all seasons.  Xf concentrations were highest in periwinkle in all seasons and at both sites, and were sufficient for BGSS acquisition year-round.  California grape and Himalayan blackberry supported Xf concentrations that were sufficient for BGSS acquisition in autumn and summer, but not in spring.  These results suggest that BGSS likely acquires Xf from riparian hosts in autumn, instead of spring.


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