Relationships of in Vitro Pathogen Inhibition and Soil Colonization to Potato Scab Biocontrol by Antagonistic Streptomyces spp

Spontaneous mutants of two scab-suppressive streptomycetes that were defective in in vitro pathogen inhibition activity were isolated. Morphological characterization of these mutants by rep-PCR genomic DNA fingerprinting or by fatty acid analysis indicated that the mutants of each parent were closely related to one another and to their respective parent, though the mutants could be differentiated from the parent strains and from one another. Despite the reduced in vitro pathogen inhibition activity, most of the mutants demonstrated significant scab biocontrol activity against pathogenic Streptomyces scabies strains. These results suggest that pathogen inhibition activity detected in vitro may not be an accurate predictor of scab biocontrol. Colonization of the suppressive strain or its mutants was generally reduced in the presence versus in the absence of the pathogen. In addition, colonization assays showed no significant differences in pathogen population density among the suppressive strain and mutant strain treatments.