Population genetics of Hyaloperonospora arabidopsidis (Hpa), a natural oomycete pathogen of Arabidopsis thaliana

Many plant pathogens cause devastating diseases, continually threatening food security worldwide. Due to the antagonistic nature of hostpathogen interactions, the interaction partners pose high selection pressures on one another. In agricultural pathosystems, which are less genetically diverse compared to wild plant pathosystems, such interactions have been well-studied, but little is known about how they play out in natural plant-pathogen systems. In 2018, we sampled wild populations of the annual plant Arabidopsis thaliana infected with a natural obligate biotrophic oomycete pathogen Hyaloperonospora arabidopsidis (Hpa) throughout a large part of their natural range in Eurasia. After propagation on immune-compromised host plants in the lab, we whole-genome sequenced 137 Hpa isolates as well as host plants from 76 populations. We expect tight co-evolutionary dynamics between both partners because of the pathogen’s host-specificity and its dependency on host resources to complete its lifecycle. We will present first insights from studying genetic diversity and population structure of Hpa. By looking closer at genomic variation within and among pathogen isolates, we aim to understand how the pathogen adapts to its host. Additionally, combining knowledge about the pathogen with information about the host, we will be able to investigate co-evolutionary dynamics in this pathosystem to deepen our understanding of natural plant-pathogen interactions