Rhynchosporium commune is a destructive pathogen of barley, causing leaf scald. Previous microsatellite studies used Syria as a representative of cultivated barley's centre of origin, the Fertile Crescent. These suggested that R. commune and Hordeum vulgare (cultivated barley) did not co-evolve in the host's centre of origin. The present study compares R. commune populations from Syria with those from Iran, which represents a secondary centre of origin for barley at the eastern edge of the Iranian Plateau. Results from this study also suggest that R. commune and barley did not co-evolve in the centre of origin of cultivated barley. This was evidenced by the low pathogen genetic diversity in Iran, which was even lower than in Syria, indicating that the pathogen may have been introduced recently into Iran, perhaps through infected barley seed. Hierarchical analyses of molecular variance revealed that most genetic diversity in Iran and Syria is distributed within populations, with only 14% among populations. Analyses of multilocus association, genotype diversity and mating type frequency suggest that Iranian populations reproduce predominantly asexually. The presence of both mating types on barley and uncultivated grasses suggest a potential for sexual reproduction. Rhynchosporium commune was also found on Hordeum murinum subsp. glaucum, H. vulgare subsp. spontaneum, Lolium multiflorum and, for the first time, on Avena sativa. The variety of wild grasses that can be infected with R. commune in Iran raises concerns of these grasses acting as evolutionary breeding grounds and sources of inoculum.

The leaf spot form of the barley disease net blotch, caused by the fungus Pyrenophora teres f. maculata (PTM), is an increasingly important foliar disease of barley. Studies of population genetic structure and reproductive mode are necessary to make predictions of the evolutionary potential of the pathogen. Sources of resistance to PTM have been found in Iranian landraces, which may have the potential to improve plant breeding efforts. However, little is known about the population genetic structure of this fungus in Iran. In this study, we analysed the frequency of the mating type genes to assess the potential for sexual mating of PTM collected from four provinces—Khuzestan, Hamadan, Golestan, and East Azerbaijan—and we investigated the population genetic structure using seven simple sequence repeat markers. High genotype diversity, linkage equilibrium, and equal ratios of mating types frequencies in the PTM populations at Khuzestan and Hamadan support the occurrence of sexual reproduction in these populations, while in Golestan and East Azerbaijan populations, significant gametic disequilibrium and relatively low genotype diversity suggest a higher incidence of clonality or different demographic histories. Unequal mating type frequencies in Golestan confirm a predominance of asexual reproduction. Finally, we found significant evidence for strong population structure with most of the genetic variation represented within regional populations (89%). Overall, our study provides evidence for high genetic variation in Iranian PTM populations, which may be the basis for rapid adaptive evolution in this pathosystem. This highlights the need for integrated efforts to control the disease.

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