Abstract
Peronospora belbahrii is one of the most destructive downy mildew diseases that has emerged throughout the past two decades. Due to the lack of quarantine regulations and its possible seed-borne nature, it has spread globally and is now present in most areas in which basil is produced. While most obligate biotrophic, plant parasitic oomycetes are highly host-specific, there are a few that have a wider host range, e.g. Albugo candida , Bremia tulasnei , and Pseudoperonospora cubensis . Recently, it was shown that Peronospora belbahrii is able to infect Rosmarinus , Nepetia , and Micromeria in Israel in cross-infection trials, hinting an extended host range for also this pathogen. In this study, a newly occurring downy mildew pathogen on lavender was investigated with respect to its morphology and phylogeny, and it is shown that it belongs to Peronospora belbahrii as well. Thus, it seems that Peronospora belbahrii is currently extending its host range to additional members of the tribe Mentheae and Ocimeae. Therefore, it seems advisable to scrutinise all commonly used members of these tribes in order to avoid further spread of virulent genotypes.