Stem rust

Wheat stem rust ( Puccinia graminis f. sp. tritici) is historically the most damaging disease of wheat. The disease has the capacity to turn a healthy looking crop, only weeks away from harvest, into nothing more than a tangle of black stems and shrivelled grains at harvest. Under suitable conditions, yield losses of 70% or more are possible. Wheat stem rust is highly mobile, spreading rapidly over large distances by wind or via accidental human transmission (infected clothing or plant material). Wheat stem rust has largely been under control for over three decades due to the widespread use of resistant cultivars. In 1999, a new virulent race of stem rust was identified from wheat fields in Uganda – popularly known as Ug99 after the year and country of discovery. Using North American scientific nomenclature, Ug99 is known as race TTKSK. Ug99 (Race TTKSK) is a cause for concern as it exhibits unique virulence patterns. No other race of stem rust has been observed to overcome so many wheat resistance genes, including the very important gene Sr31. By 2007, Ug99 (Race TTKSK) had spread via wind movements out of East Africa, into Yemen and as far as Iran. Rust pathogens change rapidly, often by mutation. Six additional variants are now recognized in the Ug99 lineage. All exhibit an identical DNA fingerprint, but differ in virulence patterns. Additional important resistance genes e.g., Sr24 & Sr36 have now been defeated by variants of Ug99. Ug99 or variants are considered a majo...

Jump To:• • • Rust diseases are among the most widespread and economically important diseases of cereal crops worldwide. Three distinct diseases, leaf rust, stripe rust and stem rust, occur on wheat and barley in North America. The fungi that cause these diseases are notorious for their ability to increase rapidly and overcome the resistance of wheat or barley varieties. The potential yield loss caused by these diseases depends on host susceptibility and weather conditions, but the loss also is influenced by the timing and severity of disease outbreaks relative to crop growth stage. The greatest yield losses occur when one or more of these diseases occur before the heading stage of development. Early detection and proper identification are critical to in-season disease management and future variety selection. Figure 1. The diagnosis of rust diseases requires some basic understanding of plant anatomy and a quick review of this information may improve the accuracy of the identification process. Emerging Races of Stem Rust Historically, stem rust has been an extremely important disease of wheat and barley. A series of severe outbreaks occurred in North America between 1900 and the 1950s, affecting grain production in the Great Plains, many Midwestern states, and Canada. More localized outbreaks of the disease occurred in the southern Great Plains as recently as 1985-1986. In all of these cases, the increased frequency and intensity of the stem rust epidemics was associated wi...

Rust diseases represent the most economically significant fungal diseases in wheat and other cereal crops worldwide, and they are widely distributed across wheat growing regions. With the capacity to form new strains of fungus, rusts can attack even previously resistant varieties. Rust diseases possess the ability to spread and travel long distances by dispersal of windborne spores and can rapidly develop under optimal weather conditions. The three rust diseases affecting wheat are leaf, stem and stripe rust. Leaf rust is the most common of the three diseases in the Central Great Plains and other wheat-growing regions in the United States. In some states, leaf rust disease occurs every year. Stem rust is not typically as prevalent as other rusts because many varieties are now resistant to the disease. Stripe rust is becoming an increasingly important disease, with recent outbreaks in the Great Plains states. Identification and lifecycle Leaf rust, also known as brown rust, is caused by the fungus Puccinia triticina.This rust disease occurs wherever wheat, barley and other cereal crops are grown. Leaf rust attacks foliage only. Identifying symptoms are dusty, reddish-orange to reddish-brown fruiting bodies that appear on the leaf surface. These lesions produce numerous spores, which can cover nearly the entire upper leaf surface. Leaf rust spores are spread by wind and splashing water. Optimal environmental conditions for development of infection are temperatures ranging fr...