Molecular phylogeny of the mycorrhizal desert truffles (Terfezia and Tirmania), host specificity and edaphic tolerance

Abstract

Terfezia and Tirmania, so called desert truffles, are mycorrhizal fungi mostly endemic to arid and semi-arid areas of the Mediterranean Region, where they are associated with Helianthemum species. The aim of this work was to study the phylogenetic relationships in these pezizalean hypogeous fungi. The restriction fragment length polymorphism (RFLP) and DNA sequences of internal transcribed spacers (ITS) of the nuclear rDNA were studied for several morphological species, Terfezia arenaria, T. boudieri, T. claveryi, T. leptoderma, T. terfezioides (=Mattirolomyces terfezioides), Tirmania nivea and T. pinoyi. The sequences were analyzed with distance and parsimony methods. Phylogenetic analyses indicated a close genetic relationship between Tirmania and Terfezia. They may have arisen from a single evolutionary lineage of pezizalean fungi that developed the hypogeous habit as an adaptation to heat and drought in Mediterranean ecosystems. This analysis also supports the re-establishment of the genus Mattirolomyces. The genera Tirmania and Terfezia were monophyletic, and morphological species corresponded to phylogenetic species. The Tirmania clade comprises desert truffles with smooth spores and amyloid asci, which were found in deserts. The Terfezia clade grouped species found in semi-arid habitats having ornamented and spherical spores. These species are adapted to exploit different types of soil (either acid or basic soils) in association with specific hosts (either basophilous or acidophilous species). Although other factors might also play a role, host specialization and edaphic tolerances (fungus and/or host tolerances) might be the key in the species diversity of these genera.

• fungal evolution
• Helianthemum
• internal transcribed spacer
• mycorrhizal fungi

We thank Dr. James M. Trappe (Forest Service, Corvallis, Oregon), Dr. Thomas D. Bruns (University of California, Berkeley, California), and anonymous reviewers for critical comments on the manuscript. We are grateful to Dr. G. Chevalier and C. Dupré (INRA, Clermont-Ferrand, France), L. Khabar (University of Rabat, Morocco) and Romero de la Osa (Forest Service, Junta de Andalucía, Spain) for providing several strains and specimens. We also thank Dr. E. Jakucs (Eotvos Lorand University, Budapest, Hungary) for his comments on Mattirolomyces terfezioides, and Dr. G. Moreno (Alcalá University) for assistance in the taxonomic identification. We are also grateful to INIA (project SC98–030) and “Vicerrectorado de Investigación de la Univ. de Alcalá” (EO28/98) for their financial support. This work was supported by a postdoctoral fellowship (EU, Contract HPMF-CT-1999-00174) and a “Ramón y Cajal” contract from the MCyT (Spain) to J. Díez.