Genetic variability and molecular phylogeny of Pleurotus eryngii species-complex isolates from Iran, and notes on the systematics of Asiatic populations

The Pleurotus eryngii species-complex includes taxa of the northern hemisphere growing in association with plants of the family Apiaceae (umbellifers). In this study, 45 Pleurotus strains were isolated from five different host-plants: Ferula ovina, F. assa-foetida, Smyrniopsis aucheri, Kellusia odoratissima, and Cachrys ferulacea; all plant species, with the exception of C. ferulacea, are reported for the first time as hosts for this fungal group. Random amplified polymorphic DNA-PCR (RAPD) analysis and nucleotide sequence data from the internal transcribed spacer of the nuclear rRNA genes (ITS1, 5.8S and ITS2) were used for assessing genetic diversity and for determining phylogenetic relationships among the populations studied. Results permitted the grouping of the strains studied into three major clusters corresponding mainly to the nature of the host-plant: the first included isolates collected from Ferula spp. only, the second included isolates originating from C. ferulacea only but from various sampling locations, and the third included all K. odoratissima and S. aucheri associated strains plus a few isolates collected from F. ovina and C. ferulacea. The grouping of the Iranian material, in conjunction with the position in the resulting phylograms of other previously obtained P. eryngii complex sequences, revealed that the first cluster is related to the asiatic 'P. nebrodensis' (or to the asiatic Ferula spp. associated Pleuroti), the second forms a rather distinct lineage which is linked with reference strains originally classified as P. fossulatus, whereas the third cluster falls within the main part (or the core) of this complex, i.e., P. eryngii. Pleurotus populations growing on umbellifers in Iran seem either to have recently diverged through a sympatric speciation process based mainly on ecological factors (e.g., P. fossulatus), or they form part of a rather wide agglomerate associated with various host-plants where exchange of genetic material is still in progress (i.e., P. eryngii).