ARS | Publication request: TEMPORAL PATTERNS OF ALMOND LEAF SCORCH DISEASE PROGRESS AND ASSOCIATED XYLELLA FASTIDIOSA GENOTYPES.

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: June 6, 2005
Publication Date: July 30, 2005
Citation: Groves, R.L., Chen, J., Viveros, M., Freeman, M., Lynn, K., Civerolo, E.L. 2005. Temporal patterns of almond leaf scorch disease progress and associated Xylella fastidiosa genotypes. Phytopathology. 95(6):S37.

Technical Abstract: Almond leaf scorch (ALS) disease has emerged as a potential threat to almond production areas throughout California’s San Joaquin Valley. The disease results from infection by the xylem-limited bacterium, Xylella fastidiosa (Xf), and the pathogen is transmitted by xylophagous insect vectors. Five orchards were surveyed in 2003 and 2004 for symptoms of ALS and (Xf) confirmed by DAS-ELISA and bacterial isolation followed by PCR. Disease incidence varied significantly between survey years and among almond cultivars in each orchard. The highest mean incidence and most severe ALS symptoms were observed in the cultivar ‘Sonora’. Isolates of (Xf) consisted of mixtures of grape or ‘G-genotype’ and almond or ‘A-genotype’ strains in surveyed orchards. Spatial analyses revealed ALS aggregates in four of the five orchards. Clusters of ALS-affected trees frequently occurred in the outermost orchard rows. Plots of semivariance in ALS incidence over distance varied in shape and magnitude between survey years and among almond cultivars. Semivariance increased over distance with increasing ALS incidence and spatial dependence was best fit by a combination of models. Increasing spatial dependence in (Xf), G-genotypes was observed at two survey locations over successive years suggesting aggregate patterns of strain distribution.