Sex in the PAC: a hidden affair in dark septate endophytes?

Background: Fungi are asexually and sexually reproducing organisms that can combine the evolutionary advantages of the two reproductive modes. However, for many fungi the sexual cycle has never been observed in the field or in vitro and it remains unclear whether sexual reproduction is absent or cryptic. Nevertheless, there are indirect approaches to assess the occurrence of sex in a species, such as population studies, expression analysis of genes involved in mating processes and analysis of their selective constraints.

Two new species of Rhynchosporium.

Rhynchosporium consists of two species, R. secalis and R. orthosporum.

Characterization of the mating type (MAT) locus in the Phialocephala fortinii s.l. -Acephala applanata species complex.

Members of the Phialocephala fortinii sensu lato -Acephala applanata species complex (PAC) are the dominant root endophytes of woody plants in temperate and boreal forests. In the present study, the mating type (MAT) idiomorphs of eight species belonging to the PAC were cloned. Because direct cloning of MAT idiomorphs was not possible, species phylogenetically placed between the PAC and other helotialean species with characterized MAT locus were used for an intermediate cloning step.

Phylogeographical analyses reveal global migration patterns of the barley scald pathogen Rhynchosporium secalis.

A phylogeographical analysis of the scald pathogen Rhynchosporium secalis was conducted using nuclear DNA sequences from two neutral restriction fragment length polymorphism loci and the mating-type idiomorphs. Approximately 500 isolates sampled from more than 60 field populations from five continents were analysed to infer migration patterns and the demographic history of the fungus. Migration rates among continents were generally low, consistent with earlier reports of significant population subdivision among continents.

Global Hierarchical Gene Diversity Analysis Suggests the Fertile Crescent Is Not the Center of Origin of the Barley Scald Pathogen Rhynchosporium secalis.

A total of 1,366 Rhynchosporium secalis isolates causing scald on barley, rye, and wild barley (Hordeum spontaneum) were assayed for restriction fragment length polymorphism loci, DNA fingerprints, and mating type, to characterize global genetic structure. The isolates originated from 31 field populations on five continents. Hierarchical analysis revealed that more than 70% of the total genetic variation within regions was distributed within a barley field.

Rapid speciation following recent host shifts in the plant pathogenic fungus Rhynchosporium.

Agriculture played a significant role in increasing the number of pathogen species and in expanding their geographic range during the last 10,000 years. We tested the hypothesis that a fungal pathogen of cereals and grasses emerged at the time of domestication of cereals in the Fertile Crescent and subsequently speciated after adaptation to its hosts. Rhynchosporium secalis, originally described from rye, causes an important disease on barley called scald, although it also infects other species of Hordeum and Agropyron.