Abstract
The existence of the causal agent of potato scab in high acid soils having a pH as low as 4.4 was confirmed in Japan. A five years survey of potato fields in the Uwaba area in Saga Prefecture revealed the occurrence of potato scab disease in high acid soils with pH values of less than 5.2. A pathogenic Streptomyces sp. forming rectiflexibile spore chains (RF type) was isolated in high density from scab lesions of potato tubers grown in high acid soil. On the other hand, a pathogenic Streptomyces sp. forming spiral spore chains (S type) was isolated in low density from the same tubers. The S type pathogens could not grow on acidic media with pH values of less than 4.5, however, that of the RF type could grow on acidic media with a pH value of 4.0. The optimum pH values for ATP production of S type and RF type pathogens were 6.0 and 5.0, respectively. Severe pathogenicity of RF type pathogen was observed in soil with a pH value of 4.4 in the field inoculation test.
