Hyaloperonospora erucae sp. nov. (Peronosporaceae; Oomycota), the downy mildew pathogen of arugula (Eruca sativa)

Arugula (or rocket; Eruca sativa) is a popular leafy vegetable often used as a salad. Downy mildew disease poses a major threat to the cultivation of this crop. Along with a quick expansion of the cultivated land of arugula, significant losses due to this disease are continuously reported worldwide. Previous studies have attributed arugula downy mildew to Hyaloperonospora parasitica (previously classified under Peronospora), applying a broad species concept, or to Peronospora erucastri, but the identity of that the causal agent is still unproven. Based on both morphology and molecular phylogeny, the arugula pathogen is revealed to be distinct from the above two species in the current study. Consequently, Hyaloperonospora erucae sp. nov. is described and illustrated, and P. erucastri affecting Erucastrum spp. is transferred to the genus Hyaloperonospora as H. erucastri comb. nov., based on morphology and phylogenetic position.