Blumeria graminis

Blumeria graminis
Scientific classification
Kingdom:	Fungi
Division:	Ascomycota
Class:	Leotiomycetes
Order:	Erysiphales
Family:	Erysiphaceae
Genus:	Blumeria
Species:	B. graminis
Binomial name
Blumeria graminis (DC.) Speer

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.

Eight special forms or formae speciales (ff.spp.) of B. graminis have been distinguished, each of which is parasitic on a particular genus of grasses. Those that infect crop plants are B. graminis f.sp. tritici, which causes powdery mildew of wheat and infects other grasses in the genera Triticum and Aegilops, f.sp. hordei on barley, f.sp. avenae on oats and f.sp. secalis on rye. Other formae speciales are pathogenic on wild grasses, including agropyri on grasses in the genera Agropyron and Elymus, bromi on Bromus spp., poae on Poa spp. and lolii on Lolium spp. (ryegrass).

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 is biotrophic, and 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.

Genetics

The genome of Blumeria graminis f. sp. hordei has recently been sequenced. [1]

References

• Pietro D. Spanu et al., Genome Expansion and Gene Loss in Powdery Mildew Fungi Reveal Functional Tradeoffs in Parasitism, in: Science. December 10, 2010[2]
• British Erysiphales[3]
• Edwards, 2002[4]
• NIAES, Microbial Systematics Lab page on Blumeria[5]
• Costamilan, 2005[6]