Taxonomic position and intraspecific variability of the nodule forming Penicillium nodositatum inferred from RFLP analysis of the ribosomal intergenic spacer and random amplified polymorphic DNA

Penicillium nodositatum induces the formation of nodules on the roots of Alnus. The analysis of RFLPs in the PCR-amplified ITS1-5.8S-ITS2 ribosomal sequence demonstrates that all the nodule-inducing strains isolated belong to a homogeneous taxon, P. nodositatum, distinct from other morphologically close species of Penicillium. A gene tree inferred from the ITS1-5.8S-ITS2 PCR/RFLP data shows that the P, nodositatum sequence clusters with those of Penicillium species belonging to subgenus Biverticillium. RAPDs generated using four 10-mer primers, allowed us to identify four distinct groups of strains in a sample of 28 strains of P. nodositatum collected in 10 different geographic sites. Only one group was found in each sampled site. No link could be established between RAPD-based groups and the geographic origin of the strains. However, our results suggest a possible link between these groups and Alnus species and/or habitats associated with each of the four French Alnus species.