Common scab, a serious disease of potatoes and other root crops, affects crop quality and market value. The disease is caused by Gram positive bacteria in the genus Streptomyces. We surveyed species in Streptomyces isolates causing potato common scab in Kagoshima and Nagasaki Prefectures, major potato-production areas in Japan. Isolates were identified as S. scabiei, S. turgidiscabies or S. acidiscabies by polymerase chain reaction (PCR) based on species-specific primers in the 16S-23S rRNA internal transcribed spacer gene (ITS) and characteristics of the pathogenicity island (PAI). About 42% of the isolates from Kagoshima Prefecture belonged to S. scabiei and about 52% to S. turgidiscabies. However, about 83% of the isolates from Nagasaki Prefecture belonged to S. scabiei. A few isolates from both prefectures belonged to S. acidiscabies. All pathogenic isolates on potato belonged to S. scabiei, S. turgidiscabies or S. acidiscabies and had genes for biosynthesis of the pathogenicity determinant thaxtomin. S. acidiscabies from Nagasaki Prefecture and Saga Prefecture lacked two genes (tomA and nec1) characteristic of the PAI. Pathogenic S. scabiei isolates belonged to two genotypes (type T or JK) based on the sequence of variable regions in the ITS. Some isolates had both genotypes (type B). In particular, all strains of S. scabiei that did not produce melanin belonged to type T. The identification using primers specific to the three pathogenic Streptomyces species agreed with morphological characteristics and physiological properties; they were almost identical to the American Type Culture Collection strains and published reference strains.
