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Techniques

A Selective Medium for the Isolation and Quantification of Pseudomonas solanacearum from Soil. W. C. Nesmith, Assistant professor, Department of Plant Pathology, Kansas State University, Manhattan, KS 66506; S. F. Jenkins, Jr., professor, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607. Phytopathology 69:182-185. Accepted for publication 14 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-182.

A new selective medium was developed for monitoring populations of Pseudomonas solanacearum in naturally and artificially infested soils. The basal medium was derived by modification of a standard triphenyl tetrazolium chloride medium (TTC). The final selective medium is prepared by adding antimicrobial compounds at the time of use. The basal medium could be stored for 60 days at room temperature and the final selective medium for 10 days at 4 C without noticeable alteration of its efficiency. Fluidal and butyrous colonies of most strains of P. solanacearum tested on the selective medium were similar in appearance to those observed on TTC medium. With the selective medium, P. solanacearum could be detected easily when as few as 100 colony forming units were added per gram of oven dry soil, but meaningful quantification was not possible with less than 10³ cells/g. Recovery of P. solanacearum was dependent on soil moisture, soil type, and bacterial strain. Most strains grew well on the selective medium and were recovered easily from soil, but some were partially or completely inhibited. Growth of other soilborne organisms seldom was observed at soil dilutions greater than 10^–3.