Evaluation of the “Most Probable Number” (Mpn) and Wet-Sieving Methods for Determining Soil-Borne Populations of Endogonaceous Mycorrhizal Fungi

The community of endogonaceous mycorrhizal fungi present in plots with two different cropping histories in a western Kentucky soybean field was analyzed by wet-sieving of spores from field soil samples and determining viability of spores of certain species with a vital stain, and by conducting a “Most Probable Number” (MPN) bioassay procedure. The MPN procedure detected 17 species, while wet-sieving of field soils detected only 10 species. Population densities of viable spores of individual species were usually lower than those of total spores, although the differences were not always statistically significant. Information from MPN bioassays on population densities of individual species is more useful than information on population densities of total propagules determined only by analysis of colonization of roots because mycorrhizal effects on plants probably are due to effects of individual species. Wet-sieving of spores from field soils and MPN bioassay of propagules both yield different and useful information, and both may often be effectively employed.