P-308 - Understanding the breakdown of resistance with population genomics: how European populations of powdery mildew overcame Pm17 resistance in wheat

To control diseases, modern agriculture relies on pesticide treatments and breeding of resistant crop varieties. However, pathogen populations can quickly evolve and overcome new control strategies. One example of such dynamics is the wheat resistance gene Pm17, which was deployed in Europe in the early 2000s to confer resistance against powdery mildew (Bgt), but it became ineffective within just a few years. Here, we used population genomics and functional assays to study the breakdown of Pm17 resistance at the molecular, functional, and population level. We sampled Bgt for two consecutive years, 2022 and 2023, and compiled a genomic dataset of 415 Bgt isolates from 22 countries in Europe and surrounding regions. We identified several loci that were under selection in the recent past, including AvrPm17. We reconstructed the recent evolutionary history of this locus and found evidence for a soft sweep on standing genetic variation. Multiple AvrPm17 variants which can partially escape recognition by Pm17 were already circulating upon its introduction, after which they rapidly expanded and spread on the whole continent. We also identified a new virulent variant, which emerged more recently and can evade Pm17 resistance altogether, suggesting that it might become dominant in the future. With this study we highlight the potential of genomic surveillance in resolving the evolutionary and epidemiological dynamics of agricultural diseases, as well as in guiding control strategies.