Today, wheat wilts, turns black and collapses in fields across Africa and Middle East, suffering from wheat stem rust, a disease caused by the air-borne pathogen Ug99, Puccinia graminis f. sp. tritici, the most virulent stem rust fungus yet to emerge. First discovered in Uganda in 1999, the fungus has been able to overcome most of the stem-rust-resistant wheat varieties developed during the past several decades. While other rusts only partially affect crop yields, Ug99 can wipe out entire wheat fields, resulting in 100% crop loss.
In cooperation with the International Maize and Wheat Improvement Center, USDA’s ARS established the first-of-its-kind Winter Wheat Stem Rust Resistance Nursery as a tool in the fight against Ug99. Located at Ankara, Turkey, the nursery has been able to distribute to 34 countries 100 lines of wheat identified by international scientists as resisting Ug99. Thirty of these were developed by ARS scientists and contain resistance to the rust in Kenya and the US. The lines variously use four or five resistant genes incorporated into winter wheat lines.
According to David Marshall, research leader of the ARS Plant Science Research Unit in Raleigh, NC, and coordinator of the wheat screening conducted in Kenya, multiple genes for resistance will slow the pathogen’s ability to readily overcome the new wheat varieties that breeders develop. The amount of time these genes can remain effective is key to maintaining resistance to stem rust in the US.
Much of the above information is from the American Bakers Association, which is actively monitoring wheat diseases and the problems these cause bakers. Read more about this research in the February 2010 issue of USDA’s Agricultural Research magazine, available online at www.ars.usda.gov/is/AR/archive/feb10/stem0210.htm.