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Isolation of Soft-Rot Erwinia spp. from Agricultural Soils Using an Enrichment Technique. J. C. Meneley, Department of Plant Pathology, University of Arizona, Tucson 85721, Present address of senior author: Standard Fruit Co., Honduras Division, Box 1689, Gulfport, MS 39501; M. E. Stanghellini, Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 66:367-370. Accepted for publication 15 October 1975. DOI: 10.1094/Phyto-66-367.

A soil enrichment technique was used to isolate soft-rot Erwinia spp. from three fallow soils previously cropped to potatoes, a fallowed cabbage soil, soil from a sugarbeet field, and soil from the rhizosphere of volunteer cabbage plants growing among potato plants. Most isolates were classified as E. carotovora var. carotovora or var. atroseptica (sensu Graham). However, all isolates produced blackleg of potato at 18 C and 24 C. The enrichment medium contained: 225 ml distilled water; 0.625 g sodium polypectate; 2.5 ml 10% (NH₄)₂SO₄; 2.5 ml 10% K₂HPO₄; and 1.5 ml 5% MgSO₄·7H₂O. The above mixture was added to 25 g of soil in a 250-ml flask and incubated anaerobically for 48 hours. Cultures were then serially diluted and plated on pectate. Colonies of soft-rot Erwinia spp. formed characteristic deep depressions in the pectate surface. The introduced Erwinia sp. was recovered 100% of the time from soils artificially infested with greater than 10 cells per gram (dry weight) of soil, 78% of the time from soils containing 2-7 cells per gram (dry weight) of soil, but only 11% of the time from soils containing 0.3 - 1.5 cells per gram (dry weight) of soil.