Rust (fungus) Rust (fungus) Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales (previously also known as Uredinales). An estimated 168 rust genera and approximately 7,000 species, more than half of which belong to the genus "Puccinia", are currently accepted. Rust fungi are highly specialized plant pathogens with several unique features. Taken as a group, rust fungi are diverse and affect many kinds of plants. However, each species has a very narrow range of hosts and cannot be transmitted to non-host plants. In addition, most rust fungi cannot be grown easily in pure culture. A single species of rust
Stem rust healthy crop about three weeks before harvest into a black tangle of broken stems and shriveled grains by harvest. Stem rust of cereals causes yield losses in several ways: Stem rust on wheat is characterized by the presence of uredinia on the plant, which are brick-red, elongated, blister-like pustules that are easily shaken off. They most frequently occur on the leaf sheaths, but are also found on stems, leaves, glumes and awns. On leaves they develop mostly on the underside but may penetrate to the upperside. On leaf sheaths and glumes pustules rupture the epidermis, giving a ragged appearance. Towards