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Pathogen Variation and Urea Influence Selection and Success of Streptomyces Mixtures in Biological Control

January 2013 , Volume 103 , Number  1
Pages  34 - 42

L. K. Otto-Hanson, Z. Grabau, C. Rosen, C. E. Salomon, and L. L. Kinkel

First, second, and fifth authors: Department of Plant Pathology, and third author: Department of Soil, Water, and Climate, University of Minnesota, St. Paul 55108; and fourth author: Center for Drug Design, University of Minnesota, Minneapolis 55455.

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Accepted for publication 21 September 2012.

Success in biological control of plant diseases remains inconsistent in the field. A collection of well-characterized Streptomyces antagonists (n = 19 isolates) was tested for their capacities to inhibit pathogenic Streptomyces scabies (n = 15 isolates). There was significant variation among antagonists in ability to inhibit pathogen isolates and among pathogens in their susceptibility to inhibition. Only one antagonist could inhibit all pathogens, and antagonist–pathogen interactions were highly specific, highlighting the limitations of single-strain inoculum in biological control. However, the collection of pathogens could be inhibited by several combinations of antagonists, suggesting the potential for successful antagonist mixtures. Urea generally increased effectiveness of antagonists at inhibiting pathogens in vitro (increased mean inhibition zones) but its specific effects varied among antagonist–pathogen combinations. In greenhouse trials, urea enhanced the effectiveness of antagonist mixtures relative to individual antagonists in controlling potato scab. Although antagonist mixtures were frequently antagonistic in the absence of urea, all n= 2 and n = 3 antagonist–isolate combinations were synergistic in the presence of urea. This work provides insights into the efficacy of single- versus multiple-strain inocula in biological control and on the potential for nutrients to influence mixture success.

© 2013 The American Phytopathological Society