STREPTOMYCES SPP. ISOLATED FROM POTATO SCAB LESIONS UNDER NORDIC CONDITIONS IN FINLAND

Actinomycetes isolated from scab lesions of potato tubers in Finland ( 60 degrees-68 degrees N, 21 degrees-31 degrees E) were characterized u sing physiological tests and production of necrosis on potato minitube rs. Seven strains were additionally analyzed for their whole cell fatt y acid profiles. The majority of the pathogenic strains were similar t o the Streptomyces scabies type strain ATCC 49173 that is characterize d by gray to brown colonies, gray spores, spiral sporophores, melanin production, and utilization of the International Streptomyces Project (TSP) sugars. However, two groups of strains (designated as Group 4, 3 8 strains; and Group 5, nine strains), each containing several pathoge nic isolates, differed from S. scabies ATCC 49173 in at least two phen otypic 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 th e iso and anteiso forms of fatty acids were different from all other s treptomycetes 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 g rew at pH 4.6 or 4.4 but not at pH 4.2.