An improved ergosterol assay to estimate fungal biomass in ectomycorrhizas

A simplified procedure for estimating fungal ergosterol from small numbers of ectomycorrhizas is described. Efficient extraction of free ergosterol is achieved with ethanol and ergosterol is then quantified by reversed-phase high performance liquid chromatography. This procedure is suitable for estimating ergosterol levels from many fungal isolates. The procedure has been scaled down allowing fungal infection to be measured in a few ectomycorrhizas. The assay is more sensitive, rapid, and convenient than chitin assay in measuring ectomycorrhizal fungus biomass. The development of symbiotic tissues and extent of fungal colonization in Eucalyptus globulus-Pisolithus tinctorius ectomycorrhizas measured by an ergosterol assay was compared to chitin assay. Ergosterol assay was more sensitive in measuring early growth of the fungal partner.