Low genetic diversity of Rhynchosporium commune in Iran, a secondary centre of barley origin

Abstract

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.

Genetic Diversity of Barley Foliar Fungal Pathogens

“…It is thought that the pathogen has entered some parts of Iran through infected seeds. The results of this study also show that R. commune and barley did not evolve together in the origin of cultivated barley [106]. Similarly, Turkey is one of the most important gene centers of barley.…”

“…Even though its sexual stage is unknown, the presence of two mating types has been reported by many researchers. Although both mating types are seen in some countries, mating type ratios indicate asexual reproduction (Iran [105], Syria [106], and Turkey [107]), while in some countries and states (Switzerland, Australia, Ethiopia, South Africa, Scandinavia, and California) [108][109][110][111], they indicate sexual reproduction. In countries where predominantly asexual reproduction is proposed, according to the null hypothesis, mating type ratios in some regions confirmed the sexual reproduction hypothesis (Turkey and Iran).…”

“…Brunner et al [113] and Zaffarano et al [109] hypothesized that the origin of the fungus R. secalis was not the Fertile Crescent or the secondary gene center of the barley plant, but that the origin of the fungus was northern Europe and spread from there to the south, North America, and Australia by various commercial or anthropogenic vectors. In addition, it has been reported by various researchers [106,107,109,113] that the genetic diversity of R. commune is low in regions where barley originates, and the genetic diversity is high in regions without barley gene centers such as Europe, Australia, and America.…”

Population genetic structure of four regional populations of the barley pathogen Pyrenophora teres f. maculata in Iran is characterized by high genetic diversity and sexual recombination

“…Moreover, barley is frequently cultivated in rotation with wheat followed by a one-year fallow. Rhynchosporium commune, in Iran also showed that the population of R. commune located in the north-east of Iran was clearly differentiated from the other populations sampled from the north-west and west of Iran(Seifollahi et al, 2018).For the PTM populations at Hamadan and Izeh, we found little population differentiation. Pathogen dispersal may be facilitated by the movement of infected plant material by farmers and plant breeders.…”

“…Similarly, a recent study of genetic variation in another fungal barley pathogen, Rhynchosporium commune , in Iran also showed that the population of R . commune located in the north‐east of Iran was clearly differentiated from the other populations sampled from the north‐west and west of Iran (Seifollahi et al, 2018).…”