Two new species of the <i>Peronospora belbahrii</i> species complex, <i>Pe. choii</i> <i>sp. nov</i>. and<i> Pe. salviae-pratensis sp. nov</i>., and a new host for <i>Pe. salviae-officinalis</i>

The downy mildew species parasitic to <i>Mentheae</i> are of particular interest, as this tribe of <i>Lamiaceae</i> contains a variety of important medicinal plants and culinary herbs. Over the past two decades, two pathogens, <i>Peronospora belbahrii</i> and <i>Pe. salviae-officinalis</i> have spread globally, impacting basil and common sage production, respectively. In the original circumscription of <i>Pe. belbahrii</i>, the downy mildew of coleus (<i>Plectranthus scutellarioides</i>) was ascribed to this species in the broader sense, but subtle differences in morphological and molecular phylogenetic analyses using two genes suggested that this pathogen would potentially need to be assigned to a species of its own. In the present study, <i>Peronospora</i> species causing downy mildew on members of the <i>Mentheae</i>, including clary sage (<i>Salvia sclarea</i>), meadow sage (<i>S. pratensis</i>), basil (<i>Ocimum basilicum</i>), ground ivy (<i>Glechoma hederacea</i>) and coleus (<i>Plectranthus scutellarioides</i>) were studied using light microscopy and molecular phylogenetic analyses based on six loci (ITS rDNA, <i>cox</i>1, <i>cox</i>2, <i>ef1a</i>, <i>hsp</i>90 and <i>β-tubulin</i>) to clarify the species boundaries in the <i>Pe. belbahrii</i> species complex. The downy mildew on <i>Salvia pratensis</i> is shown to be distinct from <i>Pe. salviae-officinalis</i> and closely related to <i>Pe. glechomae</i>, and is herein described as a new species, <i>Pe. salviae-pratensis</i>. The downy mildew on <i>S. sclarea</i> was found to be caused by <i>Pe. salviae-officinalis</i>. This is of phytopathological importance, because meadow sage thus does not play a role as inoculum source for common sage in the natural habitat of the former in Europe and Asia, while clary sage probably does. The multi-gene phylogeny revealed that the causal agent of downy mildew on coleus is distinct from <i>Pe. belbahrii</i> on basil<i>,</i> and is herein described as a new taxon, <i>Pe. choii</i>.