Taxonomic studies on streptomycetes causing potato common scab: A review.

Several Streptomyces species cause common scab of potato. The predominant pathogenic species, S. scabies, is associated with shallow, raised, and deep-pitted scab lesions. This species displays more diversity than one would expect in a conventional species. In spite of common morphological and physiological traits, S. scabies isolates vary considerably in fatty acid and protein composition. Furthermore, DNA-DNA hybridization Studies reveal that S. scabies isolates can be divided into at least three genetic groups. In addition to S. scabies, other species such as S. acidiscabies and a species related to S. albidoflavus can induce scab symptoms in potato. S. acidiscabies is characterized by its ability to cause common scab in acidic environments. The species related to S. albidoflavus usually induces deep-pitted lesions and is associated with infected tubers grown in well-irrigated soils. Virulence factors of plant pathogenic streptomycetes are still unknown but the ability to produce phytotoxins called thaxtomins is a physiological property shared by most pathogenic strains.