A SEMISELECTIVE MEDIUM AND PROCEDURES FOR ISOLATION AND ENUMERATION OF CHALARA-ELEGANS FROM ORGANIC SOIL

Recovery of Chalara elegans from soils with high organic matter conten t (76-80%) and with a high population of general microbes (fungi and b acteria) was compared using three described media. Modifications were made to a basal medium composed of carrot root extract and yeast extra ct by adding (in milligrams per liter): ampicillin, 200; chloramphenic ol, 250; nystatin, 50; oxgall, 1,000; penicillin G, 60; rose bengal, 2 5; dicloran, 6; metalaxyl, 45; and pentachloronitrobenzene, 750. The r ecovery 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 vege table fields sampled at various times during the growing seasons of 19 90 and 1991. Diluting 5 cm3 of field soil tenfold, then plating 0.5-ml portions of the suspension onto TBM-2RBA, either directly or followin g additional dilutions, and incubating dishes in the dark for 5-6 days at 22-27 C provided maximum propagule recovery. The medium proved use ful for isolating C. elegans from muck or peat soils.