Peronosporaceae

Peronosporaceae are a family of water moulds that contains 7 genera, comprising 600 species. Nested within the Peronosporaceae are the downy mildews and blue molds.

Peronosporaceae are obligate biotrophic plant pathogens. They parasitize their host plants using the haustorial apparatus to penetrate the host's tissues. Most parasitized plants are dicots. These protists reproduce by releasing entire sporangia in the same way many species release spores. The sporangia may be referred to as conidia.

Peronosporaceae of economic importance include those which have parasitic mycorrhizal relationships with grapevines. Plasmopara viticola causes a form of grape mildew. Peronospora tabacina, the "blue mold", is a saprotroph on tobacco. This species has such a delicate spore that it times its spore release for sunrise, a time of high ambient moisture and dew accumulation, so that its spores are less likely to succumb to desiccation and light. Bremia lactucae is a parasite on lettuce.