Characterization of Streptomycetes Causing Russet Scab in Québec. Esther Faucher, Groupe de Recherche en Biologie des Actinomycètes, Département de Biologie, Université de Sherbrooke, Sherbrooke (Qué), Canada, J1K 2R1. Barbara Otrysko, Éric Paradis, Nancy C. Hodge, Robert E. Stall, and Carole Beaulieu. Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec, Service des Sciences et Technologies de la pomme de terre, Station de Recherches “Les Buissons,” Les Buissons (Qué), Canada, G0H 1H0; Groupe de Recherche en Biologie des Actinomycètes, Département de Biologie, Université de Sherbrooke, Sherbrooke (Qué), Canada, J1K 2R1; Plant Pathology Department, University of Florida, Gainesville 35611; and Groupe de Recherche en Biologie des Actinomycètes, Département de Biologie, Université de Sherbrooke, Sherbrooke (Qué), Canada, J1K 2R1. Plant Dis. 77:1217-1220. Accepted for publication 26 August 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-1217.

Strains of actinomycetes causing russet scab on potato tubers were different from Streptomyces scabies and S. acidiscabies. The russet scab-inducing organisms were characterized by a bright yellow mycelium on yeast malt extract (YME) which turned brown with age, and by aerial mycelium forming flexuous spore chains which appeared as a gray mass on the colonies. The organisms utilized l-arabinose, d-fructose, d-glucose, d-mannitol, raffinose, rhamnose, sucrose, and d-xylose. They degraded xanthine and xylan, but did not produce melanin. The russet scab-inducing organisms should be placed in the genus Streptomyces, since they possessed the typical morphology, biosynthesized similar fatty acids, and produced ll-diaminopimelic acid in their cell walls, characteristic of Streptomyces species. A high level of similarity (78%) was found between the russet scab-inducing organisms and members of the cluster S. aureofaciens, indicating that both groups may be included in the same Streptomyces cluster.