ITS PRIMERS WITH ENHANCED SPECIFICITY FOR BASIDIOMYCETES - APPLICATION TO THE IDENTIFICATION OF MYCORRHIZAE AND RUSTS

We have designed two taxon-selective primers for the internal transcri bed spacer (ITS) region in the nuclear ribosomal repeat unit. These pr imers, ITS1-F and ITS4-B, were intended to be specific to fungi and ba sidiomycetes, respectively. We have tested the specificity of these pr imers against 13 species of ascomycetes, 14 of basidiomycetes, and 15 of plants. Our results showed that ITS4-B, when paired with either a ' universal' primer ITS1 or the fungal-specific primer ITS1-F, efficient ly amplified DNA from all basidiomycetes and discriminated against asc omycete DNAs. The results with plants were not as clearcut. The ITS1-F /ITS4-B primer pair produced a small amount of PCR product for certain plant species, but the quantity was in most cases less than that prod uced by the 'universal' ITS primers. However, under conditions where b oth plant and fungal DNAs were present, the fungal DNA was amplified t o the apparent exclusion of plant DNA. ITS1-F/ITS4-B preferential ampl ification was shown to be particularly useful for detection and analys is of the basidiomycete component in ectomycorrhizae and in rust-infec ted tissues. These primers can be used to study the structure of ectom ycorrhizal communities or the distribution of rusts on alternate hosts .