Landraces from mountainous regions of Switzerland are sources of important genes for stem rust resistance in barley

Stem rust, caused by Puccinia graminis f. sp. tritici, can be a serious disease problem of barley in some production areas of the world. Deployment of resistant cultivars is the best means for controlling the disease. In North America, stem rust of barley has been kept in check for more than 70 years through the widespread use of the resistance gene Rpg1, which was derived from a landrace collected in Switzerland. Rpg1 is effective against many, but not all races of P. graminis f. sp. tritici. With the threat of Rpg1-virulent races like TTKSK and QCCJB from Africa and North America, respectively, it is important that additional sources of stem rust resistance be identified in barley. Given that resistance was previously identified in germplasm from Switzerland, the primary objective of this study was to characterize a collection of Swiss barley landraces from the mountainous regions of canton Graubunden for their reaction to stem rust races TTKSK and QCCJB as well as HKHJC, which is diagnostic for detecting Rpg1. From the stem rust phenotyping of 73 barley landraces, we found a remarkably high frequency (> 43 %) of resistance to the virulent P. graminis f. sp. tritici races of TTKSK and QCCJB. In nearly every case, this resistance was due to the rpg4/Rpg5 gene complex as determined by a molecular assay. Two landraces were also found to carry Rpg1 based on their diagnostic resistant reaction to race HKHJC and presence of an amplicon specific for the gene. These results demonstrate that landraces from the mountainous areas of eastern Switzerland are valuable sources of important resistance genes for protecting barley from the devastating disease of stem rust.