Potato scab, caused by the soil-borne bacterium Streptomyces scabies, can be a serious disease of potatoes and can substantially reduce crop values on sandy, irrigated soils in the upper midwest. In Minnesota, soil in a potato breeding plot became suppressive to potato scab after long-term potato monoculture. The suppressive soil supports very high densities of antibiotic-producing, non-pathogenic Streptomyces. These organisms produce antibiotics that can kill pathogenic S. scabies and a wide variety of other fungal plant pathogens in vitro.
Application of Streptomyces isolates from the suppressive soil to potato scab-infested fields at planting has resulted in significant reductions in potato scab disease at locations in Minnesota and Wisconsin. The Streptomyces antagonists have been shown to effectively colonize the soil over multiple growing seasons, and to reduce pathogenic S. scabies populations by approximately 50%.
However, disease control using Streptomyces isolates from the suppressive soil is inconsistent over growing seasons and locations. Results to date suggest that soil type, environmental conditions, antagonist isolate, and pathogen population density and aggressiveness may all contribute to the potential effectiveness of biological control using these antagonist strains. Efforts to enhance scab biocontrol, including the use of locally adapted antagonist strains, increased inoculum doses under conditions of high disease pressure, application of purified antibiotics in conjunction with the suppressive Streptomyces, and integration of biological contol with crop rotation, are currently being studied in our laboratories.
Of further significance, we have observed significant levels of control of additional diseaes, including Septoria on aspen and a soilborne disease complex on alfalfa, following applicaion of antibiotic-producing Streptomyces to the plants or soil. Further research on the utility of pathogen-suppressive Streptomyces as a disease management tool in a variety of cropping systems in the upper midwest is underway in our laboratories.
- Linda L. Kinkel, Neil A. Anderson, Janet L. Schottel, and Deborah A. Samac, University of Minnesota
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