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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION & EPIDEMIOLOGY OF CITRUS TRISTEZA VIRUS & OTHER INVASIVE & EMERGING GRAFT-TRANSMISSIBLE DISEASES OF CITRUS IN CALIFORNIA Title: Assessing the potential of forage alfalfa crops to serve as Xylella fastidiosa, primary inoculum sources in the San Joaquin Valley

Authors
item Sisterson, Mark
item Groves, Russell - UNIV. WISCONSIN, MADISON
item Daane, Kent - UC BERKELEY

Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: October 9, 2007
Publication Date: December 12, 2007
Citation: Sisterson, M.S., Groves, R., Daane, K. 2007. Assessing the potential of forage alfalfa crops to serve as Xylella fastidiosa, primary inoculum sources in the San Joaquin Valley. In: Procedings of the Pierce's Disease Research Symposium, December 12-14, 2007, San Diego, California. p. 279-280.

Interpretive Summary: Pierce’s disease of grapes and almond leaf scorch disease are chronic problems in the San Joaquin Valley of California. Both diseases are caused by the bacterium Xylella fastidiosa; however limited information exists to characterize the primary inoculum sources for acquisition by insect vectors. We evaluated the potential of alfalfa forage crops to serve as primary X. fastidiosa inoculum sources by: 1) testing the relative susceptibility of 14 cultivars of alfalfa to infection by X. fastidiosa via needle inoculation, 2) monitoring the seasonal incidence of X. fastidiosa in alfalfa fields, and 3) documenting the seasonal level of vectors that occur in alfafa. Laboratory inoculation of fourteen cultivars of alfalfa indicated that all alfalfa cultivars tested were equally suitable hosts for X. fastidiosa. Incidence of X. fastidiosa in forage alfalfa, averaged across all field sites in the San Joaquin Valley of California, was low (0.1%). Green sharpshooter, a known vector, was found in high abundance at field sites and preferred field edges. The three cornered alfalfa hopper, whose vector competency is unknown, was more abundant in field samples than the green sharpshooter. However, laboratory tests suggest that it is not a competent vector. The results of this research will help determine the importance of alfalfa in the epidemiology of Pierce’s disease and almond leaf scorch in the San Joaquin Valley of California.

Technical Abstract: The potential for forage alfalfa to serve as a primary inoculum source of Xylella fastidiosa in the San Joaquin Valley of California was evaluated. Laboratory inoculation of fourteen cultivars of alfalfa indicated that all alfalfa cultivars tested were equally suitable hosts for X. fastidiosa. Incidence of X. fastidiosa in forage alfalfa, average across all field sites in the San Joaquin Valley of California, was low (0.1%). Green sharpshooter, a known vector, was found in high abundance at field sites and preferred field edges. The three cornered alfalfa hopper, whose vector competency is unknown, was more abundant in field samples than green sharpshooter. Greenhouse transmission tests with the three cornered alfalfa hopper did not document transmission.

Last Modified: 12/22/2014
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