Wheat can be affected by three primary rust diseases—stem, leaf and stripe rust. All share some fundamental characteristics, including being favored by wet, humid conditions. However, over the last decade, wheat production in Nebraska has been severely damaged by stripe rust. In fact, I believe this disease has now displaced the virus disease, wheat steak mosaic, as the most important and economically damaging disease of wheat in the state.
Stripe rust, caused by the fungal pathogen, Puccinia striiformis f. sp. tritici, is a serious disease occurring commonly wherever wheat is grown under cool, moist environmental conditions during the season. Worldwide, it is considered to be the primary rust disease in wheat production, and has been studied extensively for more than 100 years.
Stripe rust was described in Europe in 1827, and was first found in the United States in 1915 by a Danish visiting scientist, F. Kolpin Ravn, while traveling with a U.S. Department of Agriculture crop survey team in the western United States. Ravn clearly recognized stripe rust on wheat near Sacaton, Arizona, as it had long been a destructive problem in Great Britain, and northern and central Europe and was easily distinguished from other rusts diseases in cereals and grasses.
It was later determined to have been present in the western United States for at least 23 years, based on herbarium samples collected from Washington State, Utah, Wyoming and Montana. Other research suggested it had also been present in California in the 18th century.
After its discovery in North America, it was feared it would spread east into other major wheat growing areas (Great Plains, Mississippi valley and the Atlantic Coast). That concern, coupled with an increased need to expand wheat production during World War I, provided the stimulus for immediate research efforts. Some of these early research topics focused on economic importance, geographic distribution, host range and cultivar resistance.
By the 1930s, it had not spread into wheat growing areas east of the east of Rocky Mountains as expected. Its absence from the Great Plains reduced the emphasis for investigations and for almost 30 years (1930s to the late 1950s) there was minimal concern for the disease. During this time, no major research projects were conducted and only occasional reports of its appearance were published.
In the late 1950s and early 1960s, the disease was discovered for the first time in the Great Plains, and severe epidemics in California and the Pacific Northwest occurred as well. These reports renewed previous fears of economic losses, which then stimulated new research aimed at disease control by the USDA and state experiment stations. This was also the peak of the Cold War.
The U.S. Army began investigating the potential for using the pathogen as a biological control weapon against the Russians and their vast number of acres planted to wheat and studying the impact of the disease on national security.
Interest in the disease again waned in the late 1960s and 1970s and research was focused elsewhere. Stripe rust was noticed at this time but never became problematic east of Rocky Mountains. In the 1980s and 1990s, it began to occur periodically in south central United States (Louisiana, Arkansas and Texas) at levels that caused noticeable yield losses. However, leaf rust remained a larger problem and breeding efforts concentrated on stripe rust resistance were still not a priority. However, that began to change after 2000.