Many modern barley varieties are similar in their genotype resulting in an increased risk of occurrence of severe epidemics. There is an urgent need to broaden the genetic basis of resistance of modern barley cultivars to ensure a stable production. The identification of quantitative trait loci (QTL) conferring resistance is the basis for targeted breeding approaches aiming to improve resistance of modern cultivars. Net blotch, caused by the fungus Pyrenophora teres f. teres, Puccinia hordei, causing leaf rust, and Puccinia striiformis f. sp. hordei, the causal agent of stripe rust, are important fungal diseases of barley with the potential to cause severe yield losses and a reduction in feed and malting quality. In this thesis, the wild barley nested association mapping (NAM) population HEB‐25 was utilized to detect QTL conferring resistance against net blotch, leaf rust, and stripe rust, and evaluated in regard of its potential to improve genetic diversity and resistance of modern barley cultivars against these fungi.