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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 hostplants: 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).

Plant growth-promoting rhizobacteria possessing ACC deaminase activity reduces the level of stress ethylene, conferring resistance and improving plant growth under different stress conditions. The present study aims at evaluating Pseudomonas fluorescens strains for their potential to produce ACC deaminase and quantifying their effects on seed germination and seedling growth of wheat under salinity stress. Bacteria were first evaluated for their ability to utilize ACC, an immediate precursor of stress ethylene, using DF minimal medium containing 3 mM ACC and it was revealed that they were all able to use ACC as sole nitrogen source under in vitro conditions. Thereafter, the influence of bacterial strains on seed germination and seedling growth of wheat varieties was evaluated under NaCl induced salt stress after seven days. The experimental design was completely randomized in 3×5×5 factorial scheme with three replications. Factors consisted of salinity (0, 3 and 6 dS/m), P. fluorescens bacteria (strains PGU2-79, WBO-3, WKZ1-93 and WB1-7 and sterile water as control), and wheat variety (Chamran, Kooh-Dasht, Dehdasht, Karim and Jam). Twenty wheat seeds were transferred to plates after being soaked for an hour in bacterial suspensions at concentration of 10 8 CFU/ml. Each plate contained a filter paper which was moistened with 10 ml of NaCl solution in different concentrations. Plates were incubated in a growth chamber with maximum and minimum temperatures maintained at 20°C and 15 °C, respectively, with 12 h day-night photoperiod and relative humidity of 80%. Results revealed that P. fluorescens strains had positive impacts on different growth parameters of wheat varieties including germination percentage and rate, seed vigor, length and dry weight of coleoptile and radicle and salinity tolerance index of plants under salinity stress as compared to control. This study reveals the efficacy of plant growth promoting P. fluorescens strains containing ACC deaminase for improving salt tolerance and consequently stimulating the growth of wheat seedlings under salinity stress.

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