Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2009
Publication Date: May 23, 2009
Citation: Wanner, L.A. 2009. A patchwork of Streptomyces species isolated from potato common scab lesions in North America. American Journal of Potato Research. 86:247-265.
Interpretive Summary: Common scab disease is a serious problem for potato growers, reducing the quality and market value of the crop. We determined how many and which species of the bacteria cause this disease in potato production areas across North America. Samples were collected from field locations across the continent and also from neighboring fields. Although there were general geographic patterns in the distribution of the eight disease-causing species found, a patchwork of pathogenic species types was seen when local field sites were compared. Knowledge of what species of bacteria cause common scab and where they are found will be used by crop consultants for improving disease management by breeders developing disease-resistant potato varieties.
Common scab (CS) is a universal problem wherever potatoes are grown, but disease severity differs from place to place. About ten species have been described world-wide that cause common scab. This information has come from individual case reports and small-scale local collections. No large systematic survey of plant pathogenic Streptomyces genotypes and their prevalence has been conducted. To determine genetic variation in Streptomyces species associated with common scab in North America, more than 1400 isolates were obtained from common scab lesions. The sampling strategy included a wide geographical spread as well as multiple locations in close geographic proximity to examine regional and local species variation. Putatively pathogenic isolates belonged to eight species, most of which have been previously associated with common scab somewhere in the world. However, this is the first report in North America for three of the species. Nearly two-thirds of the isolates belonged to two species, S. scabies and S. europaeiscabiei. S. europaeiscabiei was predominant in the west and common in the northeast, while S. scabies predominated in the middle and eastern Midwest. Other species were characteristic of the western Midwest. Although there were geographic trends in species prevalence, species distribution was patchy, with single species often predominating in a field location, and neighboring field locations having different species. Additional local and regional variation was seen when isolates were genotyped for (1) repetitive sequence element patterns, reflecting the conserved or core genome, and (2) genes characteristic of the Streptomyces pathogenicity island, reflecting flexible components of the Streptomyces genome. In summary, a patchwork of pathogenic Streptomyces species and genotypes was found in potato-production regions of North America, possibly reflecting a dynamic evolutionary history. This large working collection represents the largest survey to date of the distribution of potential CS-causing Streptomyces species. The collection is a resource for population biology studies, and for tracing the evolutionary history and spread of CS-associated Streptomyces. Knowledge of the populations of scab-causing streptomycetes regionally and locally is essential in developing better management strategies and identifying or developing CS-resistant potato varieties.