Stem Rust of Wheat

Stem Rust of Wheat

One of the greatest diseases of all time, stem rust, also known as black rust or black stem rust, has plagued mankind for thousands of years. The disease can be found world wide and sporadic epidemics in the U.S. alone have resulted in yield losses as high as 200 million bushels in a single growing season. Stem rust is caused by Puccinia graminis Pers.:Pers. = P. graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn. The fungus exists in several races. Like most rust fungi it requires two taxonomically diverse hosts to complete its life cycle. The primary host is wheat. Some varieties of barley, oats and rye are also susceptible as well as wild barley and goat grass. Common barberry (Berberis vulgaris) is the most widely distributed alternate host in the United States and Europe. Allegheny barberries (B. canadensis) and some species of Mahonia also serve as alternate hosts of P. graminis f. sp. tritici. The fungus produces five spore stages. Spermagonia (pycnia) containing spermatia (pycniospores) and aecia containing aeciospores are found on the alternate woody host. Uredia (urediospores) and telia (teliospores) are found on wheat or other grassy hosts. Basidiospores are produced on germinating teliospores. The fungus over seasons as teliospores in colder climates and urediospores on fall planted wheat in warmer climates. In northern wheat growing areas (including Nebraska) urediospores that are wind blown from southern wheat areas serve as primary inoculum. Wind blown basidiospores serve as primary inoculum for the alternate woody hosts. They are disseminated in the spring and primarily infect leaf tissue. Spermatia, produced on the upper leaf surface, cross with receptive hyphae found in the same structure forming dikaryotic mycelium which grows through the leaf to the lower surface and produced an aecium. Aeciospores produced in this structure are wind blown to susceptible grassy hosts. These spores germinate and infected the host when a layer of free moisture is present on the host tissue. A reddish structure called a uredium (containing urediospores) is produced at the point of infection. The uredium is also referred to as a rust pustule. Urediospores produced on wheat serve as inoculum for secondary spread of the disease. This stage is referred to as the repeating stage. Urediospores are both produced on and reinfect wheat. Several generations of this spore type may be produced in a single growing season. When the wheat begins to mature the uredium is replaced by a telium. The telium is black in color and contains teliospores. This structure is also called a pustule. This is the overwintering stage of the fungus. However, teliospores rarely over season successfully from Kansas northward. Stem rust can develop over a wide range of temperatures (65-85^oF). The limiting environmental factor is the presence of free moisture on the host. The disease is most severe when a susceptible host is present and crop maturity is delayed.

Symptoms

Symptoms are produced on almost all aerial parts of the wheat plant but are most common on stem, leaf sheathes and upper and lower leaf surfaces. Uredial pustules (or sori) are oval to spindle shaped and dark orange-red (rust) in color. They erupt through the epidermis of the host and are surrounded by tattered host tissue. The pustules are dusty in appearance due to the vast number of spores produce. Spores are readily released when touched. Teliospores are produced in the same pustule. The color of the pustule changed from rust color to black as teliospore production progresses. If a large number of pustules are produced, stems become weakened and lodge. Symptoms are very different on the woody host. Pycnia (spermagonia) produced on the upper leaf surface appear as raised orange spots. Small amounts of honeydew that attracts insects are produced in this structure. Aecia, produced on the lower leaf surface, are yellow. They are bell-shaped and extend as far as 5 mm from the leaf surface.

Plant Health Management

Plant resistant cultivars

Eradication of woody hosts. This strategy for plant health management was aggressively pursued as early as 1660. However, it is now a more common practice to plant Japanese barberry which is not susceptible to the disease in ornamental landscapes.

Fungicide Application - Fungicides labeled for the control of stem rust include propiconazole (Tilt) and triadimefon (Bayleton) (1997). The use of these chemicals is generally cost prohibitive and not necessary as long as resistant cultivars are used.

References

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Large, E.C. 1962. The advance of the fungi. Dover Publications, Inc. New York, NY. 488 pp.

Liu, J.Q., and Kolmer, J.A. 1998> Genetics of Stem Rust Resistance in Wheat cvs. Pasqua and AC Taber. Phytopathology 88:171-176.

Nyvall, R.F. 1989. Field crop diseases handbook, 2^nd ed. Van Nostrand Reinhold. New York, NY. 817 pp.

Watkins, J.E. 1995. Rust diseases of wheat: leaf, stem, and stripe. Cooperative Extension, Institute of Agriculture and Natural Resources, and Univ. of Nebraska-Lincoln, Lincoln, NE. NebGuide G95-1245-A.

Wiese, M.V. ed., 1987. Compendium of wheat diseases, 2^nd ed. American Phytopathological Society, St. Paul, MN. 112 pp.

Useful Links

University of Nebraska

Cereal Disease Lab, University of Minnesota

University of California-Davis

Leeds University ,UK

Cornell University

Highlighted Area

Stem rust and its effects on mankind has a long and interesting history. You can find out some great facts on this disease, like its role in the pagan holiday Robigus Day, by reading the chapter entitled "The Barberry and the Wheat" from Advance of the Fungi by E.C. Large. This book is available at C.Y. Thompson and the Biology library. A special note to readers: You find references to corn rust in this chapter. In most parts of Europe, wheat is referred to as corn. Corn is called maize in these countries.

Caveat

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by:

Dr. John Watkins

Dr. W.G. Willis,

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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