Diversity of sterile root-associated fungi of two Mediterranean plants

The diversity of dark sterile mycelia (DSM) associated with the roots of neighboring healthy ectomycorrhizal Pinus halepensis and endomycorrhizal Rosmarinus officinalis plants in a Mediterranean ecosystem in Italy was investigated to assess taxonomic affinities of these poorly known root endophytes. More than 260 fungal isolates were obtained and ascribed to distinct morphotypes based on their macro- and microscopic features. Polymerase chain reaction-restriction fragment length polymorphism and sequence analyses of the internal transcribed spacers (ITS1-5.8S-ITS2) and 18S rDNA regions were carried out for representatives of the morphotypes obtained from both hosts over an 11-yr period. Molecular evidence matched morphological group circumscription. Recognition of systematic affinities was possible with varying degrees of resolution for the different morphotypes. Morph 2 was closely related to Rhizopycnis vagum (within Dothideomycetidae), Morph 1 to Diaporthe Phomopsis (within Sordariomycetidae), whereas Morphs 3a, 3b, 3c and 3d could only be given taxonomic placement at a higher level (Dothideomycetidae and Chaetothyriomycetidae). This peculiar systematic spectrum suggests that actual DSM diversity in nature is still largely underestimated. Morphophysiological convergence among morphotypes, and ecological traits possibly involved in interactions with plant hosts are discussed.