Host range of streptomycete strains causing common scab

Ten Streptomyces isolates from common scab lesions on carrots (Daucus carota) were characterized. Morphological and physiological characterization of the carrot isolates established that they were closely related to S. scabies. DNA-DNA hybridization studies were carried out between DNA from the carrot isolates and DNA from two potato strains belonging to the two genetic clusters of S. scabies. Most of the carrot isolates exhibited a high level of DNA relatedness (average of 90%) to strain EF-54, which belongs to genetic cluster 1 of S. scabies. Three carrot isolates could not be included in either S. scabies genetic cluster 1 or 2. The pathogenicity of six S. scabies isolates from potato or carrot, two isolates of S. caviscabies, and one isolate of S. acidiscabies was determined on potato, carrot, radish, beet, turnip, and parsnip. All S, scabies isolates were pathogenic on carrot and radish, but pathogenicity on beet, parsnip, turnip, and potato was variable. Even though S. acidiscabies and S. caviscabies until now have been isolated only from potato, we demonstrated that isolates of these species also could infect other crops, such as radish, carrot, parsnip, and turnip.