Blumeria graminis

Blumeria graminis (commonly called barley powdery mildew or corn mildew) is a fungus that causes powdery mildew on grasses, including cereals. 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. Previously B. graminis was included within the genus Erysiphe, but molecular studies have placed it into a clade of its own. Thus since 1975, the species graminis was moved into the new taxa Blumeria of which is the only species.Blumeria differs from Erysiphe in its digitate haustoria and in details of the conidial wall. As well Blumeria is considered to be phylogenetically distinct from Erisiphe as it is a plant pathogen that hosts solely on the true grasses of Poaceae. 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). 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. Blumeria graminis asexually produced conidia and sexually formed ascospores. Conidia were mainly distributed by wind, pests, or human activities. The water initiating ascospores were hypothesized to be dispersed not only by wind but also by splashing water-droplets. .