Tenth seminar of the new Xylella Seminar Series jointly organised by the EU funded Bexyl project, EFSA (European Food Safety Authority) and Auburn University.  Monica Donegan and Alexandra Kahn, University of California, Berkeley (USA), gave a presentation entitled Using herbarium sampling to understand Pierce’s disease of grapevines emergence in the Americas. Their research focuses on: 1) how distinct populations of Xylella fastidiosa adapt to local climates and different host plants, both in California and across the globe, and on 2) the population genetics and evolutionary adaptations of Xylella fastidiosa, with a focus on its responses to changing host environments and geographic distributions.