Hyaloperonospora brassicae

Hyaloperonospora brassicae, in the family Peronosporaceae, is a plant pathogen. It causes downy mildew of species of Brassica, Raphanus, Sinapis and probably other genera within the Brassicaceae. In the past, the cause of downy mildew in any plant in the family Brassicaceae was considered to be a single species Peronospora parasitica. However, this has recently been shown to be a complex of species with narrower host ranges, now classified in the genus Hyaloperonospora, for example Hyaloperonospora parasitica on the weed Capsella bursa-pastoris. From the perspective of plant pathology, Hyaloperonospora brassicae is now the name of the most important pathogen in this complex, attacking the major agricultural and horticultural Brassica species. Other significant Brassicaceous hosts are attacked by different species in the complex, e.g. horseradish (Armoracia rusticana) by Hyaloperonospora cochleariae, wallflower (Erysimum cheiri) by Hyaloperonospora cheiranthi.