One of the mysteries of the English language finally explained.
Definition of Peronospora in US English:
Peronospora
(also Peronosporos)
noun
MycologyA genus of fungal plant pathogens of the order Peronosporales, having sporangia borne on the tips of dichotomously branched sporangiophores and causing highly destructive plant diseases (downy mildews); (also in form peronospora) a fungus of this genus.
Origin
Mid 19th century; earliest use found in Jabez Hogg (1817–1899), ophthalmic surgeon. From scientific Latin Peronospora from ancient Greek περόνη + σπόρος.