Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2006
Publication Date: 12/1/2006
Citation: Wanner, L.A. 2006. A survey of genetic variation in streptomyces isolates causing potato common scab in the united states. Phytopathology. 96(12):1363-1371. Interpretive Summary: Common scab is a significant and recurring problem for potato growers, reducing the quality and market value of the crop. There are no available chemical controls for the disease. A variety of similar-looking but genetically different soil bacteria have been reported that can cause common scab disease. This study is the first systematic survey of what types of common scab-causing bacteria are found in potato fields in different regions of the United States. Organisms were isolated from scab lesions on field-grown potatoes from Maine, New York, Michigan, Ohio, Wisconsin and Idaho. Half of the organisms in this collection were genetically quite similar, and caused scab disease; this type was found in all six regions. The remaining organisms were more varied in appearance, and represent several genetic groups, including one group that has not been reported previously. In this relatively small survey, regional differences in scab-causing organisms were seen. This information will serve as a baseline for future studies of types and abundance of scab-causing soil bacteria. Information on the evolution and spread of new, potentially better-adapted or more virulent pathogenic strains is useful for scientists developing methods of predicting and managing common scab.
Technical Abstract: Common scab is a serious disease of potatoes and other root and tuber crops, affecting the quality and market value of the crop. The disease is caused by a genetically complex group of gram positive soil bacteria in the genus Streptomyces. Although common scab occurs wherever potatoes are grown in the world, incidence and severity vary in different locations and years. This paper reports on streptomycetes isolated from scab lesions on field-grown potatoes from Maine, New York, Michigan, Ohio, Wisconsin and Idaho. Isolates were characterized morphologically, and categorized into species groups based on sequence of variable regions in the 16s rRNA gene. The presence of genes associated with the recently described Streptomyces pathogenicity island (PAI) was also determined. About half of the isolates were genetically quite similar based both on features of the PAI and 16s rDNA sequence, grouping with the type strains of both Streptomyces scabiei (syn. S. scabies) and S. europaeiscabiei. They were found in all six regions, and are pathogenic on potato and radish. The remaining isolates included pathogens and non-pathogens. They were more varied in appearance, and represent several genetic groups, including one group that has not been reported previously. Pathogenic isolates lacking one or more gene associated with the PAI were found, although all pathogenic isolates had genes for biosynthesis of the pathogenicity determinant thaxtomin. In this relatively small survey, regional differences in scab-causing streptomycetes were seen. This report provides baseline data on the population genetics of scab-causing streptomycetes in the United States.