Diversity and population genetics of white blister rusts on Brassicaceae – towards understanding the emergence of specialised lineages and the structure of the Albugo candida population

The Albuginaceae is a monophyletic group of obligate biotrophic oomycetes that cause diseases commonly referred to as white blister rust (WBR) on a wide range of wild, weedy, and cultivated flowering plants including many high-value crops. Despite significant progress over the past two decades, which improved the understanding of the phylogenetic relationships within WBR, the actual diversity within Albuginales is still largely unknown. This is especially the case for white blister pathogens of Brassicaceae, a family of which several hundred members are known to be susceptible to WBR. For the elucidating radiation and speciation of white blister pathogens, Albugo on Brassicaceae is a promising target, as it contains both specialised species and a widely regarded as generalist species, Albugo candida. Despite its importance as the most destructive and widespread WBR pathogen of several important crops, the population structure of Albugo candida has not been explored in detail and its relationships to some closely allied host-specific species remain obscure. In the proposed research we seek to understand i) how the generalist species Albugo candida is phylogenetically linked to more specialised lineages, ii) if there is a linkage between Brassicaceae diversity and the genetic diversity of Albugo on Brassicaceae, and iii) if the population of the generalist species, Albugo candida, is panmictic or structured according to host plants or geographic regions. The findings of the proposed research will lead to new insights into the diversity, distribution and evolution of Albugo on Brassicaceae and lead to a better understanding of the emergence of new pathotypes of the disease.