BIOLOGICAL CONTROL OF PIERCES DISEASE WITH NON-PATHOGENIC STRAINS OF XYLELLA FASTIDIOSA

• Author(s): Cooksey, Donald;
• Abstract: Competitive exclusion of plant pathogens with nonpathogenic or less virulent strains has been demonstrated for a number of bacterial, fungal, and viral pathogens. Many nonpathogenic mutants retain the ability to colonize either external or internal plant tissues, and if established first, can effectively compete for colonization and establishment of pathogenic strains. One advantage of this approach for biological control is that the biocontrol agent and target pathogen occupy the same niche and have similar requirements for growth and survival. In addition, the specificity of the biocontrol interaction reduces the possibility of undesirable non-target effects. We propose to construct several nonpathogenic derivatives of Xylella fastidiosa (Xf) and test them for preemptive competitive exclusion of pathogenic strains in grape. In practice, such strains could be established in plants at the nursery level or potentially inoculated to mature vines. To construct nonpathogenic mutants, we are taking advantage of the completed genome sequence of the citrus variegated chlorosis (CVC) strain of Xf and the rough genome sequence of the almond leaf scorch strain, which is closely related to the PD strains. We predict that genes that are likely to be required for pathogenicity can be identified through comparison of these sequences with known pathogenicity gene sequences from its nearest relative, Xanthomonas campestris, or other plant or animal pathogens. PCR methods are being used to amplify these genes from the Pierces disease strain of Xf. Deletions are being created in the genes, and homologous recombination will be used to introduce each deletion independently into the Pierces disease strain. Each mutant will be tested for virulence and systemic colonization of grapevines, as well as the ability to competitively reduce populations of a pathogenic strain and reduce expression of symptoms.
• Publication Date: Dec 2001
• Journal: 2001 Pierce's Disease Research Symposium