Streptomyces spp. Isolated from Potato Scab Lesions Under Nordic Conditions in Finland.

Actinomycetes isolated from scab lesions of potato tubers in Finland (60°-68°N, 21°-31°E) were characterized using physiological tests and production of necrosis on potato minitubers. Seven strains were additionally analyzed for their whole cell fatty acid profiles. The majority of the pathogenic strains were similar to the Streptomyces scabies type strain ATCC 49173 that is characterized by gray to brown colonies, gray spores, spiral sporophores, melanin production, and utilization of the International Streptomyces Project (ISP) sugars. However, two groups of strains (designated as Group 4, 38 strains; and Group 5, nine strains), each containing several pathogenic isolates, differed from S. scabies ATCC 49173 in at least two phenotypic traits. Additionally, a single, highly virulent strain (SSC 122) differed from all other strains for its phenotypic traits. The fatty acid compositions of the three pathogenic strains of Group 4 and the strain SSC 122 differed from S. scabies ATCC 49173 and S. acidiscabies ATCC 49003. In SSC 122, the ratio of saturated and unsaturated and the iso and anteiso forms of fatty acids were different from all other streptomycetes analyzed. Thus, the strains of Group 4 and 5 and SSC 122 may represent three novel Streptomyces spp. pathogenic on potato. SSC 122 and the pathogenic strains identified to S. scabies grew at pH 5.0 but not at pH 4.6, whereas the pathogenic strains of Group 4 and 5 grew at pH 4.6 or 4.4 but not at pH 4.2.