Two novel Peronospora species are associated with recent reports of downy mildew on sages

Abstract

Recently, downy mildew of Salvia species became economically relevant globally, but the taxonomy of the causal agent remains still obscure. The objective of this study was to characterize and distinguish the different Peronospora species associated with downy mildew on sages, based on morphological and molecular data. For this purpose we compared Peronospora specimens on Salvia officinalis and Salvia plebeia with Peronospora swinglei, including the type specimen on Salvia reflexa. We observed that three Peronospora species are associated with downy mildew on sages, and the recent outbreak of the disease on S. officinalis and S. plebeia is associated with two undescribed species, contrasting the view that either P. swinglei or Peronospora lamii is the causal agent of the downy mildew disease as claimed previously by several studies. In the study presented here, we provide the formal descriptions and illustrations for the two newly introduced taxa, Peronospora salviae-plebeiae and Peronospora salviae-officinalis. The three species of Peronospora investigated seem to be restricted to specific species of Salvia: P. swinglei to S. reflexa, P. salviae-plebeiae to S. plebeia, and P. salviae-officinalis to S. officinalis. Speciation may be allopatric and closely linked to the geographic distributions of their host plants.