CHARACTERIZATION OF STREPTOMYCETES CAUSING RUSSET SCAB IN QUEBEC

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.