2008 Annual Report 1a.Objectives (from AD-416) To quantify, characterize, and spatially define the primary inoculum sources of Xylella fastidiosa present in forage alfalfa crop habitats. To document the movement and dispersal patterns of both known and potential XF insect vector species abundant in alfalfa crop habitats. 1b.Approach (from AD-416) The potential of alfalfa to serve as reservoir hosts of Xf will be quantified through field surveys to measure the seasonal incidence of the bacterium, and the seasonal abundance and dispersal of native sharpshooter vectors present within and emigrating from alfalfa. The comparative genetic structures of Xf populations obtained in reservoir alfalfa, dispersing vectors, and adjacent vineyards and orchards affected by PD and ALS, respectively, will be determined by simple sequence repeat SSR marker analysis. The relative susceptibility of selected alfalfa cultivars to infection by different genotypes of Xf will be determined by artificial inoculation and also the length of time infections of Xf genotypes can persist in susceptible cultivars. Documents Reimbursable with UC-DANR. Log 31080. Formerly 5302-22000-007-23R. (04/07) 3.Progress Report Pierce’s disease of grape and almond leaf scorch disease are both caused by the bacterial pathogen Xylella fastidiosa. The pathogen is vectored by xylem feeding insects. In the San Joaquin Valley of California, the green sharpshooter is the most abundant vector. Green sharpshooter abundance is often high in weedy alfalfa fields and alfalfa is a known host of X. fastidiosa. Thus, the role of alfalfa in the epidemiology of almond leaf scorch and Pierce’s disease was assessed. Biweekly sampling of alfalfa fields found that green sharpshooter abundance was highest on weedy field margins. Seasonal sampling of alfalfa to determine the incidence of X. fastidiosa found that incidence was low. Combined the results suggest that alfalfa may be an important source of vectors, but does not appear to be an important source of inocula. This project is monitored by submission of an annual progress report to the granting agency.