P-448 - Powdery mildews: One of the world’s most common yet understudied plant pathogens

Powdery mildews are fungal plant pathogens that affect agricultural productivity worldwide. This study evaluates the evolutionary dynamics and spread of an emerging pathogen, Erysiphe vaccinii and its impact on the global blueberry industry. Originating from North America and previously undocumented outside its native range, E. vaccinii is now reported for the first time to be spreading globally, posing significant risks to blueberry cultivation by reducing yields and increasing the need for fungicides, potentially leading to millions of dollars in losses for the blueberry industry. We have documented the presence of this pathogen across major blueberry-growing regions, including China, Morocco, Mexico, Peru, Portugal, South Africa, and the United States. Employing a multilocus approach, we analyzed both herbarium and fresh specimens collected globally, some dating back over 150 years. This analysis explored pathogen diversity, host range, and the evolutionary patterns of its spread over time and space. The study revealed 50 multilocus haplotypes and led to the classification of E. vaccinii into different formae based on host specificity, revealing two primary introductions of E. vaccinii—E. vaccinii forma convertibilis to China, Mexico, and California, and E. vaccinii f. vaccinii-corymbosi to Morocco, Peru, and Portugal. The specialization hypothesis is supported with the data showing pathogen evolution from a generalist to a specialist. The study lays the groundwork for further research into the genomic intricacies of host specialization.