RELATIONSHIPS AMONG STREPTOMYCES SPP CAUSING POTATO SCAB

The levels of DNA-DNA hybridization among members of the three major groups of Streptomyces spp. that cause potato scab did not exceed 20% for any pair. The majority of the Streptomyces scabies strains which we examined exhibited greater than 70% relatedness to the type strain, although values as low as 21% were obtained. The levels of homology between S. scabies and nonpathogenic type strains belonging to the Diastatochromogenes group ranged from 10 to 42%, while the reciprocal values obtained with labeled DNAs from Streptomyces bottropensis ATCC 25435T (T = type strain) and Streptomyces eurythermus ATCC 14975T ranged from 37 to 74% and from 2 to 24%, respectively. In contrast to S. scabies, the levels of relatedness between Streptomyces acidiscabies isolates and their type strain were high (83 to 111%). The levels of DNA relatedness within the Streptomyces albidoflavus group were uniformly low. These results are consistent with phenotypic data which indicate that pathogens in the three groups are not related. The genetic diversity of strains referred to as S. scabies exceeds the genetic diversity found at the species level, and some of these strains appear to be related to phenotypically similar nonpathogens.