Global Population Structure and Dynamics of Wheat Powdery Mildew

The global movement of pests and pathogens can often be traced to human migratory activities that include the movement of agricultural crops. The causal agent of wheat powdery mildew, the ascomycete fungus Blumeria graminis f. sp. tritici (B. graminis f. sp. tritici), is internationally distributed and one of the most rapidly adapting phytopathogens. To investigate population genetic structure, diversity and migratory potential, reduced-representation sequencing was performed on a collection of 653 B. graminis f. sp. tritici isolates from 16 countries and 6 continents. Phylogenetic inference, clustering, and population differentiation analyses were conducted, along with gene-flow estimates based on an isolation-with-migration model. The analyses revealed that the global B. graminis f. sp. tritici population is genetically differentiated into (1) older populations from Eurasia that show high internal genetic diversity and admixture with one another, and (2) genetically less diverse populations that were founded in former European colonies. Notably, Brazilian strains were phylogenetically separated from those originating in countries with a shared history of British colonization. Low gene flow suggests that natural migration of virulent isolates from abroad is limited in the former colonies. In contrast, higher estimates of gene flow among Europe, China, and Russia suggest that migration may contribute to B. graminis f. sp. tritici adaptation to novel resistance sources within Eurasia.