Geographic distribution of stem rust resistance in wheat landraces

Wheat stem rust, caused by Puccinia grami nis Pers.:Pers f. sp. tritici Eriks.& Henn., is of renewed concern due to the emergence of a new virulent race in East Africa. Landrace accessions of common wheat (Triticum aestivum L. subsp. aestivum) and durum wheat (T. turgi dum L. subsp. durum) from the National Small Grains Collection (NSGC) could be sources of new stem rust resistance genes. In an effort to better target the screening of NSGC landrace accessions against the new race, data from the NSGC were analyzed for the geographic distribution of resistance. We used data from U.S. screening trials for 5700 landrace accessions of common wheat and 2719 of durum wheat. Areas with a high incidence of stem rust resistance were found in Ethiopia, Chile, Turkey, Bosnia and Herzegovina, and adjacent areas of the former Yugoslavia. Resistance to multiple races at the seedling stage was most frequent in accessions from Ethiopia and Turkey. Resistance in durum wheat was more frequent than resistance in common wheat. The distribution of the areas with high incidence of resistant durum landraces was similar to that for common wheat landraces. A logistic regression model predicting resistance in common wheat accessions (n = 3607) from 10 traits identified 192 previously untested accessions with a greater than 50% chance of being resistant. Based on this model and on the identification of geographic centers for resistance, accessions will be prioritized for future screening against new stem rust races.