CHARACTERIZATION OF ROOT COLONIZATION PROFILES BY A MICROCOSM COMMUNITY OF ARBUSCULAR MYCORRHIZAL FUNGI USING 25S RDNA-TARGETED NESTED PCR

The aim of the present work was to study colonization patterns in root s by different arbuscular mycorrhizal fungi developing from a mixed co mmunity in soil. As different fungi cannot be distinguished with certa inty in planta on the basis of fungal structures, taxon-discriminating molecular probes were developed. The 5' end of the large ribosomal su bunit containing the variable domains D1 and D2 was amplified by PCR f rom Glomus mosseae (BEG12), G. intraradices (LPA8), Gignspora rosea (B EG9) and Scutellospora castanea (BEG1) using newly designed eukaryote- specific primers. Sequences of the amplification products showed high interspecies variability and PCR taxon-discriminating primers were des igned to distinguish between each of these four fungi. A nested PCR, u sing universal eukaryotic primers for the first amplification and taxo n-discriminating primers for the second, was performed on individual t rypan blue-stained mycorrhizal root fragments of onion and leek, and r oot colonization by four fungi inoculated together in a microcosm expe riment Tvas estimated. More than one fungus was detected in the majori ty of root fragments and all four fungi frequently co-existed within t he same root fragment. Root colonization by G. mosseae and G. intrarad ices was similar from individual and mixed inoculum, whilst the freque ncy of S. castanea and Gig. rosea increased in the presence of the two Glomus species, suggesting that synergistic interactions may exist be tween some arbuscular mycorrhizal fungi.