Rusts

Rusts are fungi of the order Uredinales. Many of these species are plant parasites. Some are superficially similar to the smuts, although their relation to each other is not clear. The taxonomy of Urediniomycota, as a whole, is in a state of flux.Many of the rusts have two or more hosts (heteroecious) and up to five spore stages. However they most commonly reproduce via asexual spore production. Their spores are airborne and can travel great distances. They mostly cause foliar infections.The group received its common name from the fact that some species have a reddish spore stage, which resembles the corrosion process known as rust.One economically important rust is wheat leaf rust, Puccinia triticina, a serious fungal disease affecting wheat and rye, which has caused serious epidemics in North America, Mexico and South America.Rust occurs on many species of plant, but in most cases any one species of rust can only infect one species of plant. This can make rust useful in biological control. The following describes the infection process of asexual spores. A picture summarizing the process can be found in the gallery below.Rust fungi are biotrophs, meaning they gain their nutrients from living cells. This requires a specialised entension of the fungus into a living plant cell called a haustorium. This develops from a haustorial mother cell. The plant cell membrane invaginates around the main haustorial body and the space between the two membranes becomes known as the extra-haustorial matrix. An iron and phosphorus rich neck band bridges the plant and fungal membranes and acts as a seal preventing the escape of nutrients into the plant apoplast. The haustorium contains amino acid and hexose sugar transporters and H+-ATPases for the active transport of nutrients from the plant cell.The rust fungus will then continue to grow and invade the plant until it is ready for sporulation.

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