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Genetic diversity studies conducted continue to document the co-occurrence of two Xf genotypes associated with ALS in affected orchards. Detection frequencies for Xf in adult GSS did vary significantly among dates with peak periods of detection occurring in May and June, 2005 averaging 28.4 and 39.7%, respectively. The mean incidence of Xf detection in dispersing populations of GSS captured was estimated at 14.9% averaging over all dates in 2005. It was documented that green sharpshooters (GSS) were the only known Xf vector speciesĬaptured on dispersal traps among experimental sites over two successive crop seasons (2004-05). The epidemiology of ALS in California's San Joaquin Valley (SJV) is not well defined and the expansion of the almond industry into this agriculturally important region may be impacted by the recent emergence of ALS. The genetic diversity of Xylella fastidiosa (Xf) population(s) associated with almond leaf scorch (ALS) disease was characterized, the temporal patterns of ALS spread were spatially analyzed, the dispersal dynamics of known vector species were monitored, and the impact of ALS on almond yield and quality was evaluated. Additional details of the research can be found in the report for the parent project 5302-22000-007- 00D, Epidemiology and Management of Xylella fastidiosa (Xf)-caused Diseases and Xf Insect Vectors. This report serves to document research conducted under a trust agreement between ARS and the Almond Board of California. Progress 10/01/05 to 09/30/06 Outputs Progress Report 4d Progress report. This project is monitored by submission of an annual progress report to the granting agency. Based on this data, a simple economic model was developed to determine the conditions under which replanting infected trees would increase returns.
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Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than that of Nonpareil. The cultivar Sonora was examined at three sites over three years and the cultivar Nonpareil was examined at one site over two years. Yield and vitality of infected and uninfected almond for the cultivars Sonora and Nonpareil were compared. As the risk of tree-to-tree spread appears to be low, the decision to remove infected trees should focus on the loss of productivity due to infection. Thus, growers are often faced with the decision to remove or keep infected trees. Currently there are no effective management techniques that prevent trees from becoming infected. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem feeding sharpshooters and spittlebugs. Almond leaf scorch disease has been present in California�s almond growing regions for over 60 years. Additional details for the research can be found in the report for the parent project 5302-22000- 008-00D, Epidemiology and Management of Xylella fastidiosa (XF) and Other Exotic and Invasive Diseases and Insect Pests. Significant Activities that Support Special Target Populations This report serves to document research conducted under a Trust Agreement between ARS and the Almond Board of California. Identify possib le Xf inoculum sources within this region.
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Characterize the genetic diversity among the Xf populations(s) assoicated with ALSD within the SJV. Approach (from AD-416) Determine which vector species transmit Xf, where they acquire the pathogen, when they move into orchards, and when they spread the pathogen to almond. Determine the extent of tree-to-tree spread and identify whether affected trees can serve as inoculum sources. Determine the comparative genetic structures of Xylella fastidiosa populations assoicated with affected almond, immigrating insect vectors, and potential reservoir hosts. Progress 10/01/04 to 01/31/08 Outputs Progress Report Objectives (from AD-416) Characterize the seasonal abundance and dispersal biology of the primary vectors of Xylella fastidiosa associated with almond leaf scorch disease (ALSD).