Submitted to: American Journal of Potato Research
Publication Type: Abstract Only
Publication Acceptance Date: March 16, 2007
Publication Date: February 20, 2008
Citation: Wanner, L.A. 2008. Altered ratios of pathogenic to non-pathogenic Streptomyces associated with lesion type and plant susceptibility to common scab. American Journal of Potato Research. 85(1):33.
Common scab symptoms and severity vary between regions in North America. To see if particular Streptomyces species or strains are associated with differences in disease pressure in scab nurseries in Minnesota and in Maine, several hundred Streptomyces isolates were characterized. Both pathogenic and non-pathogenic isolates were obtained from raised, pitted and superficial lesions and healthy skin of susceptible and resistant potato varieties. Greater numbers of non-pathogens were associated with disease-free skin, while isolates from raised or pitted lesions were nearly all pathogenic. Greater numbers of pathogenic isolates came from susceptible potato varieties, while non-pathogenic isolates predominated on resistant varieties. These observations suggest plant genotype may play a role in attracting or suppressing specific Streptomyces species. All pathogenic isolates from both locations belonged to the species Streptomyces scabies and nearly all shared several markers for pathogenicity-associated genes, although other genetic variation was observed. Further study of this variation is needed to determine its role in disease pressure differences between locations. The non-pathogenic Streptomyces species from potato skin and common scab lesions group into at least three recognizable clades, separate from the pathogenic species. Though non-pathogens are found together with pathogenic species in scab lesions, they have not acquired a pathogenicity island, suggesting the existence of natural barriers to exchange of the pathogenicity region. The role of pathogenic and non-pathogenic Streptomyces flora in common scab disease deserves further investigation. These results emphasize the need for more information on the relationship between the soil or rhizospshere microbial flora and plant disease. (Poster, Plant protection, PAA membership 657).