QUANTITATIVE ISOLATION OF THE MYCOPARASITE VERTICILLIUM-BIGUTTATUM FROM SOIL

An improved method for the isolation of the mycoparasite Verticillium biguttatum from soil was developed. Initially, soil dilution plating o nto potato dextrose agar (PDA) that had been colonized with Rhizoctoni a solani anastomosis group (AG)-3 (RPs) was used as a selective medium for V. biguttatum. This method gave 73% recovery of V. biguttatum fro m brickearth soil in comparison with only 12% recovery using the exist ing method involving distribution of soil particles onto RPs using an Andersen Air Sampler. Subsequently, acidified RPs (potato yeast dextro se agar at pH 4.0 colonized with R. solani AG-3: ARPs) were developed and recovery of V. biguttatum on this medium was equivalent to that on RPs, but V. biguttatum propagule density could be quantified in only 7 days compared to 10 days on RPs. ARPs were then used as the standard isolation medium. Recovery of V. biguttatum differed with soil type, and highest recovery was obtained on ARPs if the medium had just been overgrown by R. solani AG-3. Of a range of R. solani AGs tested, colon ization with AG-3 provided the optimal combination of a high recovery of V. biguttatum with a low contamination by the soil-microbiota, Glio cladium roseum acid other fungi were isolated from within V. biguttatu m colonies with increased frequency as soil dilution RPs and ARPs aged .