The Soil-Plate Method for Isolation of Fungi from Soil

Abstract

RESEARCH on the ecological distribution of fungi in soil, in progress in this laboratory, has been facilitated by the use of a simple plating technique, whereby soil is distributed throughout a thin layer of nutrient medium. A soil plate is prepared by transferring a small amount of the soil to be examined into a sterilized Petri dish. 8–10 ml. of cooled medium is added and the soil particles dispersed throughout the agar. With sandy soils an adequate dispersal may be obtained by shaking and rotating the plate before the agar solidifies. If, however, the soil is very dry, or contains a high proportion of clay, it is preferable to mix the particles with a drop of sterile water in the plate, before the medium is added. The amount of soil used in the preparation of a soil plate varies with the soil investigated, and is determined by trial. With many natural surface soils about 0.005–0.015 gm. of soil has been found to give a convenient number of colonies on each plate. Czapek–Dox + 0.5 per cent yeast extract agar, acidified with phosphoric acid to pH 4.0, has been found a satisfactory medium for the growth and sporulation of many soil fungi and has been extensively used as an isolation medium. A microspatula made by flattening the end of a nichrome needle has been found useful for transferring soil and crushing soil aggregates.