DIVERSITY OF THE RIBOSOMAL INTERNAL TRANSCRIBED SPACERS WITHIN AND AMONG ISOLATES OF GLOMUS-MOSSEAE AND RELATED MYCORRHIZAL FUNGI

The internal transcribed spacer (ITS) region of the nuclear ribosomal RNA was amplified, cloned and sequenced from spores of five isolates o f the arbuscular mycorrhizal fungus Glomus mosseae and one isolate eac h of G. fasciculatum, G. dimorphicum and G. coronatum. The sequences c omprised ITS1 (113-121 base pairs), 5.8S rRNA gene (154 base pairs) an d ITS2 (222-230 base pairs). The ITS sequences were at least 84% ident ical, but only distantly related to other published sequences. Their i dentification as Glomus sequences was confirmed by sequencing part of the adjoining SSU rRNA gene from one isolate; it was 98% identical to the published G. mosseae sequence. Two to four clones were sequenced f rom each isolate, and in many instances these were substantially diffe rent (up to 6% divergence) even when they were obtained from a single spore. Sequences from a single isolate were generally, but not always, more similar to each other I:han to those from different isolates. In addition to base substitutions, man) ITS sequences differed slightly in length because of the insertion or deletion of up to three nucleoti des within short runs of a single base, generally A or T. These change s were found at 22 separate sites within the ITS, and were more common between than within isolates, Phylogenetic relationships deduced from length variation and from base substitution were similar. The variati on among isolates from different continents (Europe, Asia, South Ameri ca) was no greater than among those from a smaller geographic range. T he ITS1 and 2 sequences from G. coronatum were clearly distinct from t he other isolates (11-16% divergence), but those of G. fasciculatum an d G. dimorphicum fell within the range of variation exhibited by G. mo sseae.