Isolation of Soft-Rot Erwinia spp. from Agricultural Soils Using an Enrichment Technique

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Abstract
A soil enrichment technique was used to isolate soft rot Erwinia spp. from 3 fallow soils previously cropped to potatoes, a fallowed cabbage soil, soil from a sugar beet 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.degree. C and 24.degree. 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 .cntdot. 7H2O. The above mixture was added to 25 g of soil in a 250-ml flask and incubated anaerobically for 48 h. 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 articially infested with greater than 10 cell/g (dry weight) of soil, 78% of the time from soils containing 2-7 cells/g (dry weight) of soil, but only 11% of the time from soils containing 0.3-1.5 cells/g (dry weight) of soil.

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