Genotyping of U.S. Wheat Germplasm for Presence of Stem Rust Resistance

The stem rust fungus Puccinia graminis f. sp. tritici Pers. (Pgt) has historically caused dramatic yield losses in cultivated wheat (Triticum aestivum L.). Stem rust posed a major threat to wheat production in the United States in the early 20th century, with major epidemics occurring between 1900 and the 1950s (Kolmer et al., 2007). Eff orts to remove the alternate host, com-mon barberry (Berberis vulgaris L.), and the development of lines possessing genes for resistance led to a decrease in the number and magnitude of stem rust epiphytotics (Kolmer et al., 2007). The diversity of Pgt was also greatly reduced during this time, as evidenced by the limited number of races found in recent surveys in the United States ( Jin, 2005). Without stem rust as a limitin