ARS | Publication request: ALMOND LEAF SCORCH DISEASE IN THE SAN JOAQUIN VALLEY OF CALIFORNIA: FACTORS AFFECTING PATHOGEN DISTRIBUTION

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 5, 2004
Publication Date: June 1, 2004
Citation: Groves, R.L., Chen, J., Civerolo, E.L., Viveros, M., Freeman, M., Haviland, D. 2004. Almond leaf scorch disease in the San Joaquin Valley of California: Factors affecting pathogen distribution [Abstract]. Phytopathology. 94:S36.

Technical Abstract: Almond leaf scorch disease (ALSD), caused by the xylem-limited bacterium Xylella fastidiosa(Xf), has long been present in the San Joaquin Valley (SJV). Recently, the incidence of ALSD has reemerged as a significant disease threat in many almond producing regions of the SJV. ALSD incidence was monitored within affected orchards of Fresno and Kern Counties, in California to determine patterns of disease distribution, symptom expression among affected varieties, and to determine the genotypes of Xf strains associated with ALSD. Disease incidence ranged from <1.0% to 10.2% in four surveyed orchards. With increasing disease incidence, significant aggregations of diseased trees occurred within rows in three of four orchards surveyed using ordinary runs analysis. Almond varieties including Sonora, Price, and Carmel displayed more severe leaf scorching symptoms than Nonpareil, Peerless, Norman, and Fritz. Two genomic populations of Xf were simultaneously detected in affected trees within orchards of Kern County representing both grape and almond strains. Taken together, results from these studies improve our understanding of the factors responsible for movement and distribution of the pathogen and will provide a more complete characterization of ALSD epidemiology.