Monitoring species of arbuscular mycorrhizal fungi in planta and in soil by nested PCR: application to the study of the impact of sewage sludge

Nested PCR is a highly sensitive procedure for monitoring species of arbusc ular mycorrhizal (AM) fungi and for determining their abundance in planta a nd in soil. DNA sequence variability in the D1 and D2 domains of the large ribosomal subunit is sufficient to design primers which discriminate betwee n AM fungi at the species level. The usefulness of this molecular approach is illustrated in the present study on the differential impact of sewage sl udges on a community of three AM fungi (Glomus mosseae, Glomus intraradices , Gigaspora rosea). Nested PCR was applied to trypan blue-stained mycorrhiz al root fragments and soil mycelium from pot cultures of Medicago truncatul a inoculated with the three fungi separately or together, and grown in sand containing sewage sludge that had been enriched or not with metallic or or ganic pollutants. G. intraradices and Gig. rosea varied in behaviour depend ing on whether they were inoculated alone or as a mixed community. G. mosse ae showed a similar sensitivity towards each sewage sludge whether in commu nity or alone, making it a potential candidate for ecotoxicological tests u sing M. truncatula to evaluate the quality or potential toxicity of sewage sludges which are widely used as fertilizers in agricultural lands.