Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2006
Publication Date: August 1, 2006
Citation: Mcclean, A.E., Sudarshana, P., Kluepfel, D.A. 2006. Detection of brennaria rubrifaciens the causative agent of deep bark canker (dbc)of walnut. American Phytopathological Society Annual Meeting. Technical Abstract: DBC afflicts English walnut cultivars and is characterized by late onset in trees greater than 15 years old. Symptoms include deep bleeding vertical cankers that exude a bacterial-laden reddish brown sap. We have developed a robust PCR-based technique to detect B. rubrifaciens in soil and symptomless infected trees. B. rubrifaciens produces a unique red pigment called rubrifacine, which was exploited by generating mutants defective in pigment production. Two unique insertion sites were identified that exhibited no nucleotide homology to closely related bacterial phytopathogens. The first region is homologous to nonribosomal peptide synthetases and the second has homology to the outermembrane lipoprotein sly B from enteric bacteria. PCR primers were designed to amplify these two loci involved in pigment production. We also designed PCR primers to a unique region of the 16S rDNA from this bacterium. B. rubrifaciens was detected from DNA isolated from infected walnut sap, spiked soil samples, and infiltrated walnut leaves. No amplification was observed from closely related Erwinia species or the 15 species from 6 plant-associated bacterial genera examined. These results provide a useful tool for specific and sensitive detection of B. rubrifaciens and the examination of latent infection of walnut trees by B. rubrifaciens.