The barley immune receptor Mla recognizes multiple pathogens and contributes to host range dynamics.

Funder: Gatsby Charitable Foundation; doi: https://doi.org/10.13039/501100000324Crop 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

Frequency of powdery mildew resistances in winter barley cultivars tested in domestic variety trials

In 2006–2010, resistance to the powdery mildew pathogen was studied in 225 winter barley cultivars of which 86 two-rowed and 139 six-rowed. The examined set included 59 cultivars tested in the official variety trials and 166 cultivars in variety trials conducted by domestic breeding stations in that period. Thirteen known resistances were identified (Ar, Bw, Dr2, Ha, HH, IM9, La, Ly, Ra, Ru, Sp, St and We). No resistance was found in one cultivar only. The most frequent resistance was Ra detected in 114 cultivars (= 50.7%). The resistance Bw was found in 54 cultivars (24.0%). Resistances typical for spring barley cultivars (Ly, Sp, Ru and We) were also frequent (4.0% to 23.6%). Unknown resistances were found in 20 cultivars, in nine of which they were effective to all used pathotypes of the pathogen. Thirty-six cultivars (16.0%) exhibited heterogeneity in the examined trait, i.e. they were mostly composed of lines with different resistances. Research on cultivars possessing unknown resistances continues

Genotype Heterogeneity in Accessions of a Winter Barley Core Collection Assessed on Postulated Specific Powdery Mildew Resistance Genes

Gene bank accessions are necessary for implementing many research and breeding projects. However, a great number of accessions are contaminated or confused. If such accessions are used, the results obtained from these projects are inaccurate and non-reproducible. There are methods that allow almost perfect genotype identification; nevertheless, they are relatively recent and results cannot be compared with the characteristics of the original accessions. Growing resistant cultivars is an environmentally safe and cheap way of disease management and knowledge of diverse resistance genes and their combinations can be used to identify varieties and verify their authenticity and homogeneity. For this purpose, all 172 accessions of the core collection (CC) of the Czech winter barley (Hordeum vulgare) gene bank, originating from 35 countries, were studied. For resistance tests, 51 reference isolates of Blumeria graminis f. sp. Hordei, collected in all nonpolar continents over a period of 63 years and representing the global virulence/avirulence diversity of the pathogen, were used. Only 25 barley accessions were homogeneous (genetically uniform), whereas 147 accessions were heterogeneous due to presence of different genotypes. In total, 17 resistance genes were found singly or in combinations; 76.3% of accessions with identified resistance genes carried alleles at the Mla locus. To purify the CC, progenies of individual plants must be multiplied and authenticity and homogeneity of the seed should be confirmed with resistance tests, and subsequently can be studied with more advanced methods

Rare Virulences and Great Pathotype Diversity of a Central European <i>Blumeria hordei</i> Population

Barley is an important crop grown on almost 49 Mha worldwide in 2021 and is particularly significant in Europe where powdery mildew is the most frequent disease on susceptible varieties. The most suitable way to protect crops is by exploiting genetic resistance. However, the causal agent Blumeria hordei is an extremely adaptable pathogen. The aims of this research were to increase our knowledge of the rapidly changing pathogen population and detect rare virulences. Random samples of the pathogen were obtained from the air by means of a mobile spore sampler. Spores were collected by driving across the Czech Republic in 2019, 2021 and 2023, and 299 isolates were analyzed on 121 host varieties. No infection occurred on 35 differentials, rare virulence was recorded on 31 varieties and a higher virulence frequency was found on 55 differentials. A core set of differentials along with four additional varieties distinguishes 295 pathotypes (Simple Index = 0.987) and the virulence complexity of isolates varied from 4 to 19 with an average of 10.39. The detection of new virulences, the increasing frequency of previously rare virulences and high pathotype diversity as well as high virulence complexity confirm that using nonspecific durable resistance is crucial for successfully breeding commercial varieties

Powdery Mildew Resistance Genes in Barley Varieties Bred for Human Consumption

Barley has properties that can improve and maintain human health, but to upgrade the positive characteristics of grain, specific breeding programs are required. Consumption of chemically protected food is unpopular and, therefore, genetic sources of disease resistance to the most frequent diseases are essential. The aim of this contribution is to postulate genes for powdery mildew resistance in spring barley varieties bred for human consumption. One hundred and twenty-seven breeding strains selected from thirty-three crosses, commercial varieties AF Lucius and AF Cesar developed in the program, and eight other check varieties were tested with a set of numerous pathogen isolates. Fifteen known resistance genes were found including a nonspecific resistance Mlo detected in breeding lines selected from 21 crosses. For spring barley, the utilization of Mlo is generally recommended, but its importance in varieties earmarked for human consumption should be highlighted because alternative sources of genetically more complicated resistance, derived from distant relatives or based on the accumulation of minor genes, could be economically ineffective. The presented findings enable varieties for human consumption with fully effective and durable resistance to powdery mildew to be selected

Postulation of Specific Disease Resistance Genes in Cereals: A Widely Used Method and Its Detailed Description

Cultivation of resistant varieties is an environmentally friendly and inexpensive method of crop protection. Numerous alleles of specific disease resistance occur in cereals and other crops, and knowledge of their presence in individual varieties has wide utilization in research and practice. Postulation based on phenotyping host&mdash;pathogen interactions and the gene-for-gene model is a common way of identifying these genes. The same technique and design of tests are used for postulating virulence when pathogen populations are studied. Powdery mildews caused by different formae speciales of Blumeria graminis (Bg) are important cereal diseases. In this contribution, experimental methods are described that use a model organism Bg f. sp. hordei, which can be employed for other cereal mildews and possibly rusts. It includes illustrations and a summary of our long-term practical experience. It also critically evaluates the benefits of leaf segment tests compared with screening whole plants

Virulence spectra determination in selected Blumeria graminis f. sp. hordei isolates

Virulence spectra for 14 isolates of the barley powdery mildew pathogen considered to be added to the pathogen genebank were determined. The isolates were obtained from a sample of aerial pathogen population collected across the Czech Republic in 2009. The spectra were determined on 28 barley varieties, possessing mostly specific resistance genes and inoculated with the isolates exa­mi­ned. Based on differentiation among each other, all 14 isolates showed their originality. None of the isolates exhibited increased pathogenicity to a variety with the non-specific resistance gene mlo9. All isolates were virulent on varieties carrying specific resistance genes Mla8 and Mlra, and in contrast, none of the isolates was virulent on a variety with the gene Mla23 and with a combination of genes Mla3, MlaTu2. Required characters, such as virulence on the resistance Lv or avirulence on the gene Mlh, were confirmed in some isolates. The results represent a significant step toward obtaining a complete set of information about every isolate before its including in the working genebank of the pathogen

Identification of barley powdery mildew resistances in gene bank accessions and the use of gene diversity for verifying seed purity and authenticity.

Human activities including those in crop gene banks are subject to errors, especially during seed multiplication and maintenance of seed germination. Therefore, the most serious problem of gene banks is authenticity of the accessions and their genotypic purity. There are many methods for determining the identity of varieties, but comparisons between current data and past records are not easy since the latter are often missing. Breeding barley resistant to powdery mildew caused by Blumeria graminis f. sp. hordei (Bgh) was traditionally based on incorporating major genes into new varieties and the results have been published. Our goal was to identify resistance genes to powdery mildew in accessions of the Czech spring barley core collection and compare these data with earlier information to establish the authenticity of the accessions. Two hundred and twenty-three accessions of the collection including 665 single plant progenies were tested. Sixty-four selected reference isolates of Bgh representing the world diversity of the pathogen were used for resistance tests. Twenty-two known resistance genes were postulated either separately or in combinations. In the collection, 151 homogeneous accessions were found, but the resistances of nine of them were inconsistent with published data and in 12 accessions their authenticity is doubtful. The remaining 72 accessions were heterogeneous and comprised 176 resistance genotypes, 54 of which were probably mechanical admixtures of other varieties. There are several pathogens of cereals, e.g. rusts and mildews, against which many resistance genes in host crops have also been exploited. Knowledge of these resistances can assist in maintaining pure and genuine stocks in gene banks. Seed purity and the authenticity of accessions can subsequently be checked with more advanced methods