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Evaluation of Selective Media for Isolation of Soft-Rot Bacteria from Soil and Plant Tissue. Diane Cuppels, Specialist, Department of Plant Pathology, University of Wisconsin, Madison 53706; Arthur Kelman, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 64:468-475. Accepted for publication 10 October 1973. DOI: 10.1094/Phyto-64-468.

A medium (CVP) containing NaNO3, sodium polypectate, and crystal violet was compared with other selective media for the isolation of soft-rot bacteria from soil. Pectolytic colonies of Erwinia spp. could be distinguished from those of Pseudomonas spp. by the type of depressions formed in the pectate medium and colonial morphology. Recovery of E. carotovora and E. atroseptica from field soil on CVP range from 65 to 100%, depending upon soil type and the number of bacteria added to soil samples. Approximately 96% of the natural soil bacteria (ca. 6 × 107 cells/g dry wt soil) were eliminated on CVP. Addition of manganese sulfate (monohydrate) to CVP further reduced the soil bacterial populations without markedly lowering the percent recovery of soft-rot Erwinia. When CVP was used for detection of soft-rot bacteria in soil samples from cabbage, carrot, and potato fields, fluorescent pseudomonads (not soft-rot Erwinia) were the pectolytic gram-negative bacteria most frequently isolated.

Additional keywords: Pseudomonas marginalis, blackleg.