Conspecificity of DAOM 197198, the model arbuscular mycorrhizal fungus, with Glomus irregulare: molecular evidence with three protein-encoding genes

Ribosomal nuclear genes are routinely utilized in the molecular identification of fungi. The variation in the multiple copies of these genes within each Glomeromycota strain and species reduces their usefulness for molecular characterization of arbuscular mycorrhizal fungi. To explore the potential of molecular tools for the identification of Glomus species, a multi-gene analysis approach was undertaken. Three protein-encoding genes were tested, namely elogation factor 1-alpha (765 bp), V-H+-ATPase VHA5 (1468 bp), and F0F1-ATPase beta-subunit (621 bp). The latter is newly reported for the Glomeromycetes. Eleven species, including the type-specimen of Glomus irregulare Blaszk., Wubet, Renker & Buscot, a reference strain of G. intraradices N.C. Schenck & G. S. Sm. (DAOM 225240), and five strains of Glomus sp. formerly identified as G. intraradices, were analysed. These genes did not show polymorphisms within strains, and results indicated a close relationship between molecular identification and morphological characterization. Species with closely related spore morphological features, G. aggregatum N.C. Schenck & G. S. Sm., G. diaphanum Morton & Walker, G. irregulare, and Glomus sp. DAOM 197198, showed more than 99% nucleotide similarity, while the morphologically distinct species, G. cerebriforme McGee, G. clarum T. H. Nicolson & N.C. Schenck, G. claroideum N.C. Schenck & G. S. Sm., G. custos C. Cano & Dalpe, G. mosseae (T. H. Nicolson & Gerd.) Gerd. & Trappe, and G. proliferum Dalpe & Declerck, showed less than 97% similarity for at least one gene. A 100% molecular similarity for all three genes was found between G. irregulare and Glomus sp. DAOM 197198, confirming the new identity of the model arbuscular mycorrhizal fungus. Similarity thresholds for identification by DNA sequencing are discussed.