Blumeria graminis

Blumeria graminis is a fungus that causes powdery mildew on grasses, including cereals (called barley powdery mildew or corn mildew). It is the only species in the genus Blumeria. It has also been called Erysiphe graminis and (by its anamorph) Oidium monilioides or Oidium tritici.

Systematics
Previously B.graminis was included within the genus Erysiphe, but the molecular studies have placed it into a clade of its own. Blumeria differs from Erysiphe in its digitate haustoria and in details of the conidial wall. Parasitic specialized strains are differentited for each plant and grouped as formae speciales (f. sp.), the most important of which are ''Blumeria graminis f. sp. tritici, Blumeria graminis f. sp. hordei and Blumeria graminis f. sp. avenae''.

Morphology
The mycelium can cover the plant surface almost completely, especially the upper sides of leaves. Ascocarp is dark brown, globose with filamentous appendages, asci oblong. Ascospores hyaline, ellipsoid, 20-30 x 10-13 µm in size. Anamorph produces on hyaline conidiophores catenate conidia of oblong to cylindrical shape, not including fibrosin bodies, 32-44 x 12-15 µm in size. Haustoria are palmate.

Ecology
Blumeria graminis disperses by scattering conidia and ascospores. It does not grow on synthetic media. Relatively cool and humid conditions are favourable for its growth. Its relatively great genetic variability enables it often to infect previously resistant plant varieties.