Identification of Potato Scab Inducing and Suppressive Species of<i>Streptomyces</i>

Complementation, co-plating, antibiotic, and taxonomic tests were used to identify pathogenic and suppressive species of Streptomyces. Of 17 strains of Streptomyces (16 from potato tubers and one from garden beet), 13 were determined to be S. scabies, two were S. diastatochromogenes, one was S. albogriseolus, and one could not be identified. Only the 13 S. scabies strains and the one unidentified russet scab strain were pathogenic on leaf-bud tubers. Prototrophs between auxotrophic mutants formed only in intraspecies pairings, and for S. scabies at rates of 1. 11 and 1.43% for intra- and interstrain pairings, respectively. Tests involving inhibitory reactions of paired strains supported the taxonomic study. In co-plating tests, the type A (lethal zygosislike) reaction occurred only in interspecies pairings. The type B reaction indicated production of and sensitivity to inhibitory compounds. Antibiotic assays confirmed the type B reactions and placed the 17 strains into seven groups that were consistent with the taxonomic work. Three strains, two S. diastatochromogenes and one S. albogriseolus, obtained from a potato scab plot that had become suppressive, produced antibiotic-like compounds against highly pathogenic strains of S. scabies