Fifteen powdery mildew resistance genes and the gene MlaN81 derived from ‘Nepal 81’were found in 76 Czech and Slovak spring and winter barley cultivars when tested for reaction to a set of powdery mildew isolates. Nine cultivars (‘Donum’, ‘Expres’, ‘Jubilant’, ‘Orbit’, ‘Primus’, ‘Progres’, ‘Stabil’, ‘Vladan’ and ‘Zlatan’) are composed of lines with different resistance genes. The Mlat gene is present in nine cultivars and was transferred from the Anatolian landrace ‘A‐516′. The resistances derived from ‘KM‐1192’and ‘CI 7672’were identical and designated Ml(Kr). Five winter barley cultivars possess the Ml(Bw) resistance. The winter barley line ‘KM‐2099’carries the mlo gene. The parental cultivar ‘Palestine 10’was also tested in which the genes Mlk1, MlLa were identified. The German cultivar ‘Salome’, a parent of seven cultivars tested, probably carries the gene MlLa in addition to mlo and Mla7. The gene mlo6 may be present in the cultivar ‘Heris’. Most of the results were confirmed by the pedigrees of the cultivars.

In the last two decades, resistance to the powdery mildew pathogen has been investigated in a large number of barleys in the Czech Republic. Several tens of winter barley cultivars were identified with a resistance based on an unknown gene or unknown combinations of resistance genes. In this paper tests on 20 of these cultivars are presented. Thirty-two reference isolates of Blumeria graminis f.sp. hordei were used. All the 20 cultivars shared a particular, previously unknown resistance. Landi was the first cultivar registered with this resistance and it is recommended that this resistance be designated Ln. Isolates virulent to Ln were already found randomly in old European, and also in non-European pathogen populations, where cultivars possessing the resistance Ln were never grown. On the other hand, the resistance Ln has been highly effective even 13 years after Landi registration.

Powdery mildew caused by the airborne ascomycete fungus Blumeria graminis f. sp. hordei (Bgh) is one of most common diseases of barley (Hordeum vulgare). This, as with many other plant pathogens, can be efficiently controlled by inexpensive and environmentally-friendly genetic resistance. General requirements for resistance to the pathogens are effectiveness and durability. Resistance of barley to Bgh has been studied intensively, and this review describes recent research and summarizes the specific resistance genes found in barley varieties since the last conspectus. Bgh is extraordinarily adaptable, and some commonly recommended strategies for using genetic resistance, including pyramiding of specific genes, may not be effective because they can only contribute to a limited extent to obtain sufficient resistance durability of widely-grown cultivars. In spring barley, breeding the nonspecific mlo gene is a valuable source of durable resistance. Pyramiding of nonspecific quantitative resistance genes or using introgressions derived from bulbous barley (Hordeum bulbosum) are promising ways for breeding future winter barley cultivars. The utilization of a wide spectrum of nonhost resistances can also be adopted once practical methods have been developed.

Crop losses caused by plant pathogens are a primary threat to stable food production. Stripe rust (Puccinia striiformis) is a fungal pathogen of cereal crops that causes significant, persistent yield loss. Stripe rust exhibits host species specificity, with lineages that have adapted to infect wheat and barley. While wheat stripe rust and barley stripe rust are commonly restricted to their corresponding hosts, the genes underlying this host specificity remain unknown. Here, we show that three resistance genes, Rps6, Rps7, and Rps8, contribute to immunity in barley to wheat stripe rust. Rps7 cosegregates with barley powdery mildew resistance at the Mla locus. Using transgenic complementation of different Mla alleles, we confirm allele-specific recognition of wheat stripe rust by Mla. Our results show that major resistance genes contribute to the host species specificity of wheat stripe rust on barley and that a shared genetic architecture underlies resistance to the adapted pathogen barley powdery mildew and non-adapted pathogen wheat stripe rust.

Powdery mildew, caused by Blumeria graminis f. sp. hordei (Bgh), is a worldwide disease problem on barley (Hordeum vulgare) with potentially severe impact on yield. Historically, resistance genes have been identified chiefly from cultivated lines and landraces; however, wild barley (H. vulgare subsp. spontaneum) accessions have proven to be extraordinarily rich sources of powdery mildew resistance. This study describes the characterization of a collection of 316 wild barley accessions, known as the Wild Barley Diversity Collection (WBDC), for resistance to powdery mildew and the genetic location of powdery mildew resistance loci. The WBDC was phenotyped for reaction to 40 different Bgh isolates at the seedling stage and genotyped with 10 508 molecular markers. Accessions resistant to all 40 isolates of Bgh were not found; however, three accessions (WBDC 053, 085 and 089) exhibited resistance to 38 of the isolates. Gene postulation analyses revealed that many accessions, while resistant, contained none of the 12 genes present in the Pallas near‐isogenic lines Mla1, Mla3, Mla6, Mla7, Mla9, Mla12, Mla13, Mlk1, MlLa, Mlg, Mlat and Ml(Ru2), suggesting that the accessions carry novel genes or gene combinations. A genome‐wide association study of powdery mildew resistance in the WBDC identified 21 significant marker‐trait associations that resolved into 15 quantitative trait loci. Seven of these loci have not been previously associated with powdery mildew resistance. Taken together, these results demonstrate that the WBDC is a rich source of powdery mildew resistance, and provide genetic tools for incorporating the resistance into barley breeding programmes.