Population structure of Puccinia graminis, the cause of stem rust on wheat, barley, and rye in Sweden

Sammanfattning: Rust fungi belong to the phylum Basidiomycetes, order Uredinales cause damage on almost all plants, including cereal crops. Some of the species within the genus Puccinia causes rust disease on cereal crops. One example of a disease from this genus is Puccinia graminis, which historically has caused severe damage in cereal crop production. During recent years, P. graminis have re-emerged in Sweden on barley and wheat. The aim of this work was to examine if the same population of P. graminis infects both wheat and barley in Sweden. In total 204 samples were collected of the crops, 123 from barley (Hordeum vulgare), 10 from rye (Secale cereale) samples and 71 from wheat (Triticum aestivum) in 16 farmers’ fields. The genotypic diversity was examined based on microsatellite markers and the population structure and genetic relationship within and between the collected samples were analysed. The results indicate that the P. graminis population on barley and wheat seemed to be partially divided in two clusters. However, the clusters were partially overlapping, and the main branches of barley and wheat had smaller branches of barley and wheat within them. The rye samples were spread mainly in the barley cluster or branch, but more samples are needed to draw conclusions about the rye population. This could indicate that the P. graminis population on barley and wheat are not fully genetically separated consisting of a meta-population, but that there probably is a selection on the different cereal hosts. The result did also confirm that there is a high genetic diversity within the populations, indicating that sexual recombination can be completed on the aecial host Berberis spp. in Sweden. There was no correlation with geographic and genetic distance, confirming that there is mostly wind dispersal of P. graminis.