Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: March 21, 2003
Publication Date: June 21, 2004
Citation: Wanner, L.A. 2003. Molecular and pathogenic variation in streptomycetes causing common scab [abstract and talk]. Phytopathology 93 (6):S89 Supplement
Common scab is the fourth most important potato disease, and affects root and tuber crops world-wide. Scab is caused by streptomycetes, phylogenetically diverse soil-inhabiting gram-positive bacteria. Most are not plant pathogens. To better understand pathogenesis and variability in symptoms, we are investigating pathogenicity determinants and virulence factors in plant pathogenic streptomycetes. Pathogenicity is associated with production of the toxin thaxtomin and with a proposed pathogenicity island (PAI) containing a gene for a pathogenicity factor (nec1) within a conserved region that may be horizontally transferred into distantly related streptomycetes to produce plant pathogenic strains. We isolated streptomycetes from scabby potatoes from several US states. Disease varied in severity and appearance in potato and radish. All pathogenic isolates contain the txtA gene, but several do not produce the pigment melanin, and a few lack the nec1 gene. We further characterized the putative PAI using PCR, Southern blotting and sequence analysis. In contrast to our expectation of conservation in this region, we find variation among plant pathogenic strains.