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A Semiselective Medium and Procedures for Isolation and Enumeration of Chalara elegans from Organic Soil. S. Chittaranjan, Graduate Research Assistant, Centre for Pest Management, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6. Z. K. Punja, Associate Professor and Director, Centre for Pest Management, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6. Plant Dis. 77:930-932. Accepted for publication 11 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0930.

Recovery of Chalara elegans from soils with high organic matter content (7680%) and with a high population of general microbes (fungi and bacteria) was compared using three described media. Modifications were made to a basal medium composed of carrot root extract and yeast extract by adding (in milligrams per liter): ampicillin, 200; chloramphenicol, 250; nystatin, 50; oxgall, 1,000; penicillin G, 60; rose bengal, 25; dicloran, 6; metalaxyl, 45; and pentachloronitrobenzene, 750. The recovery of pathogen propagules from artificially infested soil on this semiselective medium (TBM-2RBA) was about 80%. The pathogen also was recovered from naturally infested field soil from four commercial vegetable fields sampled at various times during the growing seasons of 1990 and 1991. Diluting 5 cm3 of field soil tenfold, then plating 0.5-ml portions of the suspension onto TBM-2RBA, either directly or following additional dilutions, and incubating dishes in the dark for 56 days at 2227 C provided maximum propagule recovery. The medium proved useful for isolating C. elegans from muck or peat soils.

Keyword(s): black root rot, inoculum density, Thielaviopsis basicola.