Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/23/2005
Publication Date: 7/30/2005
Citation: Chen, J., Groves, R.L., Civerolo, E.L., Viveros, M., Freeman, M., Zheng, Y. 2005. Colony morphology of Xylella fastidiosa almond leaf scorch strains and their genomic and diagnostic implications. Phytopathology. 95:S18.
Technical Abstract: Xylella fastidiosa is the causal agent of almond leaf scorch disease (ALSD) and is currently re-emerging in California as a production problem. In addition to X. fastidiosa genotypic data, phenotype information, or the expression of genes, is equally important for understanding the epidemiology and the genetics of this pathogen. We examined the colony morphologies of strains of two X. fastidiosa genotypes isolated from ALSD-affected trees in California. Although significant variations occurred during more than 14 sub-culturing passages, the colony morphology associated with each genotype could be found among most strains. Best differentiations were in the early passage cultures. G-genotype strains were typically smooth with entire margin. Most of the A-genotype strains were “pit”-like, or umbonate with a smooth convex center and rough surface in the outskirt. Both A-genotype and G-genotype strains produced colony imprints or surface etchings on PWG medium, suggesting enzymatic depolymerization of gellan polysaccharide. Two candidate genes for gellan depolymerization were identified in silico. The colony morphology data in conjunction with PCR genotyping was used to survey genotype distribution in the central and southern San Joaquin Valley of California. We conclude that the two genotypes did not spread simultaneously.