Summary
Stem rust, caused by Puccinia graminis, has historically been one of the most economically important pathogens of the small grain cereals (wheat, barley, oats, and rye) in the U.S. Northern Great Plains (especially: Minnesota, North Dakota, and South Dakota). Annual yield losses due to stem rust in the region often exceeded 10% and were substantially greater during severe epidemics. This disease has been of minor importance in recent decades, especially for wheat; however a highly virulent race of the pathogen was identified in Africa that can infect the majority of the wheat and barley varieties currently grown in this region. This race, called Ug99 (or TTKST), has recently been found in the Middle-East (as of 2008) and could again become a serious issue for wheat and barley in the United States if it becomes established here. Please note that the author is in South Dakota (USA) and therefore some of this material may not be relevant to other locations or cropping systems.
Pathogen Information & Symptoms
Puccinia graminis is a heteroecious, macrocyclic rust. That is, it has five different spore stages and requires two different hosts to complete its life cycle. The most economically important stage of P. graminis is the uredinial stage. Spores of this stage (urediniospores) are asexual (clonal), produced during the growing season, and can re-infect the same host species that they were produced from. For example, urediniospors of P. graminis f.sp. avenae are produced from infected oat plants and can re-infect oats (the same plant, even). The other spore stages that are able to infect plants, i.e. aeciospores and basidiospores, do not infect the same host that they came from but a different host. For example, the aeciospores produced from barberry plants are only able to infect a grass host (e.g. wheat).
P. graminis has a relatively wide host range for a rust and is somewhat atypical in this manner for the genus Puccinia. Most members of this genus are only able to infect a limited number of host species, often a single genus for each of the uredinal and aecial stages. This species has several formae speciales (similar to sub-species) that tend to differ significantly in their host ranges, although there is some overlap with the f.sp. that are pathogenic on grasses. P. graminis can infect most of the foliar tissues of susceptible species and on the uredinal hosts (e.g. wheat), this includes the leaves, leaf sheaths, stems, and spikes (flowering tissues). On the alternate host (e.g. barberry), infection is usually limited to leaves. The table below contains the f.sp. that are pathogens of the small grain cereals and most pertinent to our research.
Species |
Primary Hosts in U.S. (Uredinial stage) |
Comments |
|---|---|---|
Puccinia graminis f.sp. avenae |
oat (Avena sativa), wild oat (A. fatua) |
Occasionally causes economic losses in commercial oats crops. |
Puccinia graminis f.sp. secalis |
rye (Secale cereale), barley (Hordeum vulgare) |
Of limited economic importance in recent years. |
Puccinia graminis f.sp. tritici |
wheat (Triticum aestivum), Durum ( T. turgidum), barley (Hordeum vulgare), Quack grass (Elytrigia repens), Foxtail Barley (Hordeum jubatum) |
Occasionally causes economic losses in commercial wheat or barley crops. Most have been minor <5% in recent years. |
Several of the links below have more thorough descriptions of the lifecycle and biology of this pathogen.