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Chitosan (CS), derived from the partial deacetylation and hydrolysis of chitin, varies in the degree of deacetylation, molecular weight, and origin, influencing its biological effects, including antifungal properties. In plants, CS triggers immune responses and stimulates biomass growth. Previously, we found that the antifungal activity of CS was strongly dependent on its physicochemical properties. This study revealed that the chitosan batch CS_10 with the strongest antifungal activity also effectively activated plant immune responses and promoted biomass growth. Barley treated with CS_10 exhibited systemic acquired resistance (SAR), characterized by micronecrotic reactions upon Puccinia hordei (Ph) inoculation and reduced symptoms following Fusarium graminearum (Fg) infection, representing biotrophic and necrotrophic pathogens, respectively. CS_10 treatment (concentration 200 ppm) also enhanced plant biomass growth (by 11% to 15%) and promoted the accumulation of salicylic acid (SA), a hormone that regulates both plant immune responses and growth. Low levels of exogenous SA applied to plants mirrored the stimulation observed with CS_10 treatment, suggesting SA as a key regulator of CS_10-induced responses. Transcriptomic analysis identified SA-regulated genes as drivers of enhanced immunity and biomass stimulation. Thus, CS_10 not only fortifies plant defenses against pathogens like Ph and Fg but also boosts growth through SA-dependent pathways. [ABSTRACT FROM AUTHOR]

Background: Currently, cultivar mixtures are being extensively used in agriculture worldwide. The current research study aimed to identify the optimal proportion of cultivars with different resistance to pathogens to reduce the severity of leaf diseases in mixed cultivars against net blotch and leaf rust of barley. Methods: Leaf rust severity was assessed using a modified Cobb scale, and net blotch severity with the E. E. Geshele scale. Disease severity was averaged from triplicate measurements on 25–30 plants. After harvest, 1000 seeds per plot were weighed. Differences were evaluated using the Fisher test (α = 0.05), and correlations via the Chaddock scale in Statistica 13.3. Results: A high degree of inverse correlation was established between the proportion of resistant cultivars and the severity by both diseases r= – 0.93/– 0.99. The optimal mixture combination of a resistant and susceptible cultivar against net blotch was recorded as 1S:4R, and leaf rust as 1S:3R and 1S:4R. Conclusion: In mixed barley crops, a strong inverse correlation was found between the proportion of resistant cultivars and disease severity (r = –0.93/–0.99). Disease severity correlated directly with humidity and temperature in spring, with an inverse correlation for net blotch in June. Using mixed cultivars enhances crop resistance to abiotic and biotic stresses, making it suitable for eco-friendly farming. [ABSTRACT FROM AUTHOR]

Barley crops are at risk of being attacked by several leaf diseases. Net blotch, brown rust, Rhynchosporium and Ramularia leaf spot are among the most widespread and can cause severe attack and yield losses. Two trial protocols targeting Ramularia and net blotch, respectively, have been tested in several countries in 2021 and 2022. Ramularia trials were situated in Germany, Ireland, Scotland, and Denmark. The net blotch trials were placed in Denmark, Belgium, the UK, Germany, Finland, and France. In the two protocols, 12–13 different fungicide solutions including co-formulations of DMIs, SDHIs, QoIs, and multi-site inhibitors have been tested to compare efficacy and yield responses. Against Ramularia leaf spot, the fungicides were applied at GS 47–51 and against net blotch at GS 37–45. In six trials, the efficacy against Ramularia leaf spot was scored. The results showed a superior control from the co-formulation fluxapyroxad + metyltetraprole (78–100% control), but also solo mefentrifluconazole and the mixtures fluxapyroxad + mefentrifluconazole performed well (average 74–76% control). The mixture fluxapyroxad + metyltetraprole provided the best yield increase followed by Ascra Xpro. Folpet as a solo solution was inferior. Following the net blotch protocol, only three trials developed enough disease to rank the different fungicides; however, in five trials ranking against brown rust was also possible. Most treatments gave very good control of net blotch, and brown rust (> 80% control). The mixture fluxapyroxad + metyltetraprole delivered the best control against all diseases overall. Average yield responses from eight trials showed very similar increases from the tested fungicides. [ABSTRACT FROM AUTHOR]

Rust fungi are devastating plant pathogens, and several Puccinia species have exerting substantial financial impacts on global barley cultivation. Fungicides are used on a large scale as an effective method for combating phytopathogenic fungi. The negative environmental impacts of fungicides are steadily escalating on a daily basis. Consequently, researchers are currently exploring alternative approaches to mitigate the use of fungicides, such as the utilization of plant extracts. This method has proven effective due to its incorporation of natural antifungal substances. Among the nine natural elicitors that were tested, the application of plant extracts on barley seedlings resulted in an increase in the incubation and latent periods of Puccinia hordei. These periods are integral components of partial and induced resistance, effectively mitigating the incidence of barley leaf rust disease by over 70% on mature plants. Similarly, the biochemical analyses demonstrated a notable augmentation in all the tested treatments' overall phenolics and oxidative enzyme activities (peroxidase and polyphenol oxidase). Random amplified polymorphic DNA (SCoT) test serves as a viable approach for assessing the impact of plant extracts and microorganisms on barley plants. The results obtained from this study indicate that the detection of DNA polymorphism through SCoT analysis holds a significant potential powerful tool to evaluate genetic changes compared with untreated plants although some of them tested displayed high similarities at the morphological reaction. [ABSTRACT FROM AUTHOR]

Barley leaf rust (Puccinia hordei Otth.) is considered a harmful disease that occurs in barley-growing regions worldwide. In Russia, the disease is among the most prevalent in the Krasnodar region, which is the leader in the production of barley grain and has a favorable climate for disease development. In this paper, we studied the efficiency of 17 varieties and lines of barley from the International and Australian sets containing currently known Rph resistance genes or their combinations to P. hordei in the field, and 15 varieties and lines in the seedling phase in greenhouse conditions during 2019–2021. We concluded that the lines carrying the Rph7 and Rph13 genes remained immune throughout the three years of studies in the seedling and adult plant stages. The Rph1 and Rph23 genes showed moderate efficiency during the three years. The Rph2, Rph3, Rph4, Rph5, Rph6+2, Rph8, Rph12, Rph19, and Rph21+2 genes showed low efficiency over the three years. This was also confirmed by the results of their assessment in the seedling phase: the number of monopustular isolates virulent to lines with the majority of the studied genes for three years was above 90%. Fluctuations in the virulence of the P. hordei population were observed under sufficiently unfavorable weather for disease development in 2019, 2020, and 2021. This proves the ability of the fungus to adapt to changing conditions. Therefore, annual monitoring of the response of lines and varieties carrying resistance genes and studying the virulence of the pathogen are crucial for the selection of rust-resistant varieties, and, hence, the prevention of barley leaf rust epidemics in all grain-producing regions worldwide. [ABSTRACT FROM AUTHOR]

Previous studies investigating the performance of transmission and reflection datasets for disease detection showed inconsistent results. Within the studies, the performance of transmission imaging varied significantly for the detection of biotroph and necrotrophy plant pathogens, while reflection imaging showed excellent results in both studies. The current study explores the hypothesis that the disparity between these results might be correlated with the different interactions of the respective pathogens with the host plants and the way light interacts with the plant tissue. Pyrenophora teres f. teres and Puccinia hordei—the causative agents of net blotch and brown rust in barley—have been investigated with focus on early-stage detection and quantification (disease severity) of symptoms. Datasets of hyperspectral imaging time-series measurements were analysed through application of multiple data analysis methods (support vector machines; principal component analysis with following distance classifier; spectral decomposition) in order to compare the performance of both datasets for the detection of disease symptoms. It could be shown that transmittance-based brown rust detection (e.g. 12% disease severity) is outperformed by reflectance-based detection (e.g. 36% disease severity) regardless of the algorithm. However, both the detection and quantification of brown rust through transmittance were more accurate than those of powdery mildew in earlier studies. Transmittance and reflectance performed similar for the detection of net blotch disease during the experiments (~ 1% disease severity for reflection and transmission). Each data analysis method outperformed manual rating in terms of disease detection (e.g. 15% disease severity according to manual rating and 36% through support vector machines for rust reflection data). Except for the application of a distance classifier on net blotch transmittance data, it could be shown that pixels, which were classified as symptomatic through the data analysis methods while estimated to represent healthy tissue during manual rating, correlate with areas at the edges of manually detected symptoms. The results of this study support the hypothesis that transmission imaging results are highly correlated with the type of plant–pathogen interaction of the respective pathogens, offering new insights into the nature of transmission-based hyperspectral imaging and its application range. [ABSTRACT FROM AUTHOR]

In many production areas, barley (Hordeum vulgare L.) is attacked by the leaf rust pathogen (Puccinia hordei Otth), a basidiomycetous fungus that reduces both its yield and quality. Many leaf rust resistance genes, known as reaction to P. hordei (Rph) genes, have been described in barley. To differentiate genetic variants for virulence in pathogen populations, plant pathologists use differentials (i.e., sets of host lines carrying different resistance genes). The sources of Rph1–15 were derived from cultivars, landraces, and wild barley (H. vulgare ssp. spontaneum K. Koch) accessions with diverse geographic origins and agromorphological traits. Ideal differential sets comprise single‐gene lines backcrossed to a single adapted accession that is susceptible to all known races of a pathogen. In this study, sources of Rph1–15 and other Rph gene donors were backcrossed to the susceptible barley cultivar Bowman and then genotyped to characterize the chromosomal positions and sizes of introgressions. Overall, 95 Bowman introgression lines for leaf rust resistance were developed and characterized for their rust phenotypes and genotypes. A single line was selected to represent each of the 15 Rph genes for use as the new barley leaf rust differential set. The existence of possible new resistance genes in the studied germplasm was postulated. The new Bowman Rph1–15 differential lines will facilitate the efficient virulence phenotyping of P. hordei and serve as valuable genetic stocks for Rph gene stacking and cloning in barley. [ABSTRACT FROM AUTHOR]

Breeding for adult plant resistance (APR) is currently impeded by the low frequency of annual field‐based testing and variable environmental conditions. We developed and implemented a greenhouse‐based methodology for the rapid phenotyping of APR to leaf rust in barley to improve the efficacy of gene discovery and cloning. We assessed the effects of temperature (18 and 23°C) and growth stage (1–5 weeks) on the expression of APR in the greenhouse using 28 barley genotypes with both known and uncharacterized APR. All lines were susceptible in week 1, while lines carrying Rph20 and several with uncharacterized resistance expressed resistance as early as week 2. In contrast, lines lacking Rph20 and carrying either Rph23 and/or Rph24 expressed resistance from week 4. Resistant phenotypes were clearest at 18°C. A subset of 16 of the 28 lines were assessed for leaf rust across multiple national and international field sites. The greenhouse screening data reported in this study were highly correlated to most of the field sites, indicating that they provide comparable data on APR phenotypes for screening purposes. [ABSTRACT FROM AUTHOR]

In this study, we characterized and mapped a new and rare resistance gene ( Rph FT) in the Chinese barley variety 'Fong Tien'. Rph FT, a dominant gene, was mapped to chromosome 5 HL at a genetic position of 142.1 cM using DArT-seq markers. The gene was also confirmed to be present in Australian cultivar 'Yagan' based on allelic tests, and likely 'Lockyer' based on multipathotype tests. The genetic studies also confirmed the presence of Rph12 in Australian cultivar 'Baudin'. Rph12 is also located on chromosome 5 HL close to Rph FT, and the two loci were confirmed to be independent. Gene Rph FT is of limited breeding value because it is effective to only one pathotype of P. hordei, 220P+ + Rph13 in Australia; nevertheless, it may play a role in controlling leaf rust if used in combination with other Rph genes. The locus symbol Rph25 is recommended for Rph FT in accordance with the rules and numbering system of barley gene nomenclature. [ABSTRACT FROM AUTHOR]

A collection of 112 African barley accessions were assessed for response to Puccinia hordei in seedling greenhouse tests using 10 pathotypes and in adult plant field tests over three successive field seasons in Australia. One of the 10 pathotypes (viz. 5457P?) used in seedling tests was also used in field tests to allow assessment of the presence of adult plant resistance (APR) in lines that were seedling susceptible to this pathotype. The seedling resistance genes Rph1, Rph2, Rph3, Rph9.am and Rph9.z were postulated in a number of accessions, singly and in various combinations, with Rph2 and Rph9.z being the most common. Twenty-six accessions carried seedling resistance that was either uncharacterized or could not be determined using the 10 P. hordei pathotypes. One accession carried high levels of APR and 11 accessions showed moderate levels of APR, all of which were susceptible to all P. hordei pathotypes at the seedling stage. All barley accessions were genotyped for the presence of marker alleles that are closely linked to the APR genes Rph20 and Rph23 (bPb-0837 and Ebmac0603, respectively). No accession was positive for bPb-0837, suggesting that Rph20 is not frequent in African germplasm. Thirteen accessions were postulated to carry Rph23 based on the presence of the marker allele Ebmac0603 found in Yerong (Rph23), and 10 out of the 11 accessions with moderate APR lacked the bPb-0837 and Ebmac0603 marker alleles, indicating that they likely carry new uncharacterized APR genes. Inheritance studies were performed using populations derived from four of the accessions that carried APR (Clho 9776, Clho 11958, Mecknes Maroc and Sinai) by crossing with the susceptible barley genotype Gus. Chi squared analysis of the phenotypic data from F3 populations suggested that CIho9776 carried a single APR gene and CIho11958, Mecknes Maroc and Sinai each carried two genes for APR to leaf rust. [ABSTRACT FROM AUTHOR]

Barley (Hordeum vulagare L) is the major crop for the people living in the high hills and mountainous region of Nepal. Leaf rust (caused by Puccinia hordei) is one of the major production threats for barley cultivation. A lot of variation can be observed on Nepalese barley accessions with respect to leaf rust resistance characteristics. Two hundred and forty one barley accessions were screened for leaf rust resistance characteristics on heading stage at Khumaltar, Lalitpur, Nepal. Among them, one hundred and nine Nepalese barley accessions showing promising for disease resistance were screened using six SSR markers linked to leaf rust resistance genes. Bonus and Local Jau was used as the resistant and susceptible check respectively. Leaf rust resistance genes Rph1, Rph2, Rph3, Rph7, QBLR-P and QTL on chromosome 5HS were detected on Nepalese barley accessions using respective SSR markers. Eight Nepalese barley accessions showed presence of three and more leaf rust resistant genes. The poor relationship between the field disease resistance and molecular markers linked with specific leaf rust resistance gene proved that Nepalese barley gene pool contains other leaf resistance genes. [ABSTRACT FROM AUTHOR]

Cereal rusts, caused by obligate and biotrophic fungi in the genus Puccinia, are important diseases that threaten world food security. With the recent discovery of alternate hosts for the stripe rust fungus ( Puccinia striiformis), all cereal rust fungi are now known to be heteroecious, requiring two distinct plant species serving as primary or alternate hosts to complete their sexual life cycle. The roles of the alternate hosts in disease epidemiology and pathogen variation vary greatly from species to species and from region to region because of different climatic and cropping conditions. We focus this review on rust fungi of small grains, mainly stripe rust, stem rust, leaf rust, and crown rust of wheat, barley, oat, rye, and triticale, with emphases on the contributions of alternate hosts to the development and management of rust diseases. [ABSTRACT FROM AUTHOR]

Background Barley is an important cereal crop cultivated for malt and ruminant feed and in certain regions it is used for human consumption. It is vulnerable to numerous foliar diseases including barley leaf rust caused by the pathogen Puccinia hordei. Results A temporarily designated resistance locus RphCantala (RphC) identified in the Australian Hordeum vulgare L. cultivar 'Cantala' displayed an intermediate to low infection type (";12 = N") against the P. hordei pathotype 253P- (virulent on Rph1, Rph2, Rph4, Rph6, Rph8 and RphQ). Phenotypic assessment of a 'CI 9214' (susceptible) x 'Stirling' (RphC) (CI 9214/Stirling) doubled haploid (DH) population at the seedling stage using P. hordei pathotype 253P-, confirmed that RphC was monogenically inherited. Marker-trait association analysis of RphC in the CI 9214/Stirling DH population using 4,500 DArT-seq markers identified a highly significant (-log10Pvalue > 17) single peak on the long arm of chromosome 5H (5HL). Further tests of allelism determined that RphC was genetically independent of Rph3, Rph7, Rph11, Rph13 and Rph14, and was an allele of Rph12 (Rph9.z), which also maps to 5HL. Conclusion Multipathotype tests and subsequent pedigree analysis determined that 14 related Australian barley varieties (including 'Stirling' and 'Cantala') carry RphC and that the likely source of this resistance is via a Czechoslovakian landrace LV-Kvasice-NA-Morave transferred through common ancestral cultivars 'Hanna' and 'Abed Binder'. RphC is an allele of Rph12 (Rph9.z) and is therefore designated Rph9.am. Bioinformatic analysis using sequence arrays from DArT-seq markers in linkage disequilibrium with Rph9.am identified possible candidates for further gene cloning efforts and marker development at the Rph9 / Rph12 / Rph9.am locus. [ABSTRACT FROM AUTHOR]

In the last years fluorescence spectroscopy has come to be viewed as an essential approach in key research fields of applied plant sciences. However, the quantity and particularly the quality of information produced by different equipment might vary considerably. In this study we investigate the potential of three optical devices for the proximal sensing of plant-pathogen interactions in four genotypes of spring barley. For this purpose, the fluorescence lifetime, the image-resolved multi spectral fluorescence and selected indices of a portable multiparametric fluorescence device were recorded at 3, 6, and 9 days after inoculation (dai) from healthy leaves as well as from leaves inoculated with powdery mildew (Blumeria graminis) or leaf rust (Puccinia hordei). Genotype-specific responses to pathogen infections were revealed already at 3 dai by higher fluorescence mean lifetimes in the spectral range from 410 to 560 nm in the less susceptible varieties. Noticeable pathogen-induced modifications were also revealed by the 'Blue-to-Far-Red Fluorescence Ratio' and the 'Simple Fluorescence Ratio'. Particularly in the susceptible varieties the differences became more evident in the time-course of the experiment i.e., following the pathogen development. The relevance of the blue and green fluorescence to exploit the plant-pathogen interaction was demonstrated by the multispectral fluorescence imaging system. As shown, mildewed leaves were characterized by exceptionally high blue fluorescence, contrasting the values observed in rust inoculated leaves. Further, we confirm that the intensity of green fluorescence depends on the pathogen infection and the stage of disease development; this information might allow a differentiation of both diseases. Moreover, our results demonstrate that the detection area might influence the quality of the information, although it had a minor impact only in the current study. Finally, we highlight the relevance of different excitation-emission channels to better understand and evaluate plant-physiological alterations due to pathogen infections. [ABSTRACT FROM AUTHOR]

Lesion mimic mutants of plants have the feature of spontaneously displaying necrotic spots or bands on their leaves. Lesion mimics have often displayed enhanced resistance to biotrophic pathogens whilst showing increased susceptibility to necrotrophs. This paper identifies three novel, non-allelic mutants of barley ( Hordeum vulgare), which spontaneously form necrotic leaf lesions: Necrotic leaf spot 9.3091 ( nec9. 3091), Mottled leaf 8.1661 ( mtt8. 1661) and Mottled leaf 9.2721 ( mtt9. 2721). The Necrotic leaf spot 8.3550 mutant ( nec8. 3550), formerly known as bst1, was included in the study because it is a lesion mimic mutant belonging to the same original pool. The reactions of the mutants to the biotroph Puccinia hordei and the necrotroph Pyrenophora teres f. sp . teres were investigated. Mutants nec8. 3550 and mtt8. 1661 were more resistant than the parental Bowman near-isogenic line with the Rph3.c gene (Bowman Rph3.c, NGB 22452) to leaf rust, caused by P. hordei. Mutants nec8. 3550, mtt8. 1661 and mtt9. 2721 were more susceptible than Bowman Rph3.c to net blotch, caused by P. teres f. sp. teres. Autofluorescence was detected in leaf tissues of all mutants. Based on the high expression of the PR1 and Hv- HIR genes, combined with the low susceptibility to P. hordei, nec8. 3550 appears to have entered a state of systemic acquired resistance, which is quite distinct from the resistance expressed in mtt8. 1661. The latter mutant has low or no expression of PR1 and Hv- HIR genes, yet it is highly resistant to rust. It is also extremely susceptible to net blotch. These mutants can serve as genetic sources of novel disease resistance for barley improvement. [ABSTRACT FROM AUTHOR]

Abstract: Wild barley (Hordeum vulgare subsp. spontaneum) accession ‘Shechem 12–32’ is resistant to multiple pathogens, including Puccinia hordei and Cochliobolus sativus, causal agents of leaf rust and spot blotch, respectively. Both pathogens begin the infection process as biotrophs, but C. sativus switches to necrotrophism after colonization. It is generally considered that plants require distinct arsenals of genes to successfully respond to either biotrophic or necrotrophic pathogens. To characterize the defense responses initiated by resistant wild barley accession ‘Shechem’, a temporal survey of transcript abundance after inoculation with P. hordei and C. sativus was conducted using the Barley1 GeneChip. A total of 95 and 299 gene transcripts exhibited significant (p < 0.0001) differential accumulation in response to P. hordei and C. sativus, respectively, compared to mock-inoculated controls, with 21 transcripts (6 defense-related) in common. Quantities of differentially accumulated gene transcripts in response to P. hordei were evenly distributed across examined time points, while over one-half (183) of the differentially accumulating gene transcripts in response to C. sativus were identified at 24 h after infection, the approximate time when the pathogen changes trophic lifestyles. Our results indicate that resistant wild barley exhibits a different host response to biotrophic and hemibiotrophic pathogens, with genes related to oxidative stress having a particularly important role in defense against hemibiotrophs. [Copyright &y& Elsevier]

• Partial resistance is considered race-nonspecific and durable, consistent with the concept of ‘horizontal’ resistance. However, detailed observations of partial resistance to leaf rust ( Puccinia hordei) in barley ( Hordeum vulgare) revealed small cultivar × isolate interactions, suggesting a minor-gene-for-minor-gene interaction model, similar to so-called ‘vertical’ resistance. • Three consistent quantitative trait loci (QTLs), labelled Rphq2, Rphq3 and Rphq4, that were detected in the cross susceptible L94 × partially resistant Vada have been incorporated into the L94 background to obtain near-isogenic lines (NILs). Three isolates were used to map QTLs on seedlings of the L94 × Vada population and to evaluate the effect of each QTL on adult plants of the respective NILs under field conditions. • Rphq2 had a strong effect in seedlings but almost no effect in adult plants, while Rphq3 was effective in seedlings and in adult plants against all three isolates. However, Rphq4 was effective in seedlings and in adult plants against two isolates but ineffective in both development stages against the third, demonstrating a clear and reproducible isolate-specific effect. The resistance governed by the three QTLs was not associated with a hypersensitive reaction. • Those results confirm the minor-gene-for-minor-gene model suggesting specific interactions between QTLs for partial resistance and P. hordei isolates. [ABSTRACT FROM AUTHOR]

An inventory of 481 lines derived from 12 Ethiopian barley (Hordeum vulgare L.) landraces and the checks was made for partial resistance to Puccinia hordei under greenhouse and field conditions at Adet, Ambo and Sinana Agricultural Research Centers in 2003 and 2004 cropping seasons in Ethiopia. The experiments were laid out in a triple lattice design. Each plot consisted of two rows of 1-m long with spacing of 0.20 m between rows. The overall mean leaf rust epidemics varied from area under disease progress curve (AUDPC) of 86 to 1,835. The disease was as high as AUDPC 1,378 on the susceptible check L94. Highly significant variations were recorded between and within the landraces/lines in leaf rust incidence, severity, days to heading, plant height, thousand seed weight and yield. Similarly, the variations between and within barley groups from three altitude areas and three ear-types were significant. Landraces 1686, 3255, 3262 and 3783 had the least and landraces 219900, 3975 and 3980 had the highest leaf rust severity. Of the 481 lines tested, 413 (86%) had significantly lower disease than the susceptible check, but not than the partial resistant check Vada. In contrast, the yields were more for lines with less disease than for those with high. The frequency of resistant landraces/lines was more in altitude 2,301–2,500 m, and irregular and two rows ear-types than in lower altitude areas and six rows ear-type. Nevertheless, the correlation and regression analysis revealed the adverse effect of the disease in the yields of barley. The 413 lines with high infection types at seedling stage and lower AUDPC under field conditions possess partial resistance to leaf rust. [ABSTRACT FROM AUTHOR]

Leaf rust, caused by Puccinia hordei, is a serious threat to barley ( Hordeum vulgare L.) production. Genes Rph5 and Rph7 confer resistance to many of the most prevalent races of P. hordei in the United States and Europe, respectively. The reliability and diagnostic capabilities of several molecular markers for these two genes were evaluated and validated for use in gene postulation, marker-assisted selection (MAS) and eventual pyramiding of genes Rph5 and Rph7 with other effective resistance genes. Fifty-eight winter barley experimental lines developed at Virginia Polytechnic Institute and State University, as well as seven barley cultivars were phenotyped for reaction to three diverse isolates of P. hordei and genotyped with molecular makers closely linked to genes Rph5 and Rph7. Sequence tagged site markers TC2863-12.4 and ABG70 as well as simple sequence repeat marker AY642926-CA11 were reliable and diagnostic in gene postulation and have potential for use in MAS and pyramiding of genes Rph5 and Rph7. Comparison of phenotypic and genotypic data revealed that one barley line VA04H-95 has genes Rph5 and Rph7 and at least one unknown gene. [ABSTRACT FROM AUTHOR]

A set of 23 recombinant lines (RLs) of barley ( Hordeum vulgare L.) derived from H. vulgare × H. bulbosum L. crosses was inoculated with barley leaf rust ( Puccinia hordei) and powdery mildew ( Blumeria graminis f.sp. hordei) at the seedling stage to identify their levels and mechanisms of resistance. Eight RLs were studied further in glasshouse and field tests. All three barley parents (‘Emir’, ‘Golden Promise’ and ‘Vada’) were highly susceptible to powdery mildew and leaf rust isolates. Several RLs showed partial resistance expressed as high relative latency periods and low relative infection frequencies against leaf rust. This high level of partial resistance was due to a very high level of early aborting colonies without host cell necrosis. Several RLs showed hypersensitive resistance to some or all isolates. For powdery mildew, one RL was completely resistant to the CC1 isolate and had a hypersensitive resistance to the CO-02 isolate. Three RLs derived from ‘Emir’ were completely resistant to both powdery mildew isolates, and three more RLs tested in the field had higher levels of partial resistance than their parents. The results indicate that H. bulbosum contains major and minor gene(s) for resistance to leaf rust and powdery mildew that can be transferred to cultivated barley. [ABSTRACT FROM AUTHOR]

Three barley cultivars, Shyri, Clipper and Terán, with different levels of partial resistance to barley leaf rust, caused by Puccinia hordei, were exposed to six levels of the pathogen. These levels were obtained by 5, 4, 3, 2, 1 and 0 fungicide (Propiconazol) applications respectively and occurred every 15 days starting at 66 days after sowing. No application served as the control treatment. There were three replicates. The six-row plots were surrounded by a row of a highly susceptible barley cultivar in which the barley leaf rust arrived naturally in a fairly early plant stage. The disease severity was assessed five times with 15 days intervals starting at 66 days after sowing. The yields were determined by harvesting the inner four rows of the plots. An analysis of variance was carried out on the area under the disease progress curve (AUDPC) data and on the yield data. ‘Shyri’ was the least susceptible cultivar, ‘Terán’ the most. The percentage yield losses varied with the six levels of pathogen from 0 to 31.5% (‘Shyri’), from 0 to 46% (‘Clipper’) and from 0 to 63.5% (‘Terán’). The yield losses correlated strongly with the AUDPC, the linear correlation coefficient being 0.97. The yield losses indicate the importance of the pathogen in Ecuador. It also means that high levels of partial resistance are needed to prevent significant yield damage. [ABSTRACT FROM AUTHOR]

The article reports on a study of the genetic diversity in Puccinia hordei, the causal agent of barley leaf rust. Six primer-pair combinations of amplified fragment length polymorphism were utilized and a total of 782 polymorphic markers were produced. Results indicated that molecular diversity in P. hordei can be linked to virulence, but not well with the place of origin.

We used a well-characterized barley mapping population (BCD 47 × Baronesse) to determine if barley stripe rust (BSR) resistance quantitative trait loci (QTL) mapped in Mexico and the USA were effective against a reported new race in Peru. Essentially the same resistance QTL were detected using data from each of the three environments, indicating that these resistance alleles are effective against the spectrum of naturally occurring races at these sites. In addition to the mapping population, we evaluated a germplasm array consisting of lines with different numbers of mapped BSR resistance alleles. A higher BSR disease severity on CI10587, which has a single qualitative resistance gene, in Peru versus Mexico suggests there are differences in pathogen virulence between the two locations. Confirmation of a new race in Peru will require characterization using a standard set of differentials, an experiment that is underway. The highest levels of resistance in Peru were observed when the qualitative resistance gene was pyramided with quantitative resistance alleles. We also used the mapping population to locate QTL conferring resistance to barley leaf rust and barley powdery mildew. For mildew, we identified resistance QTL under field conditions in Peru that are distinct from the Mla resistance that we mapped using specific isolates under controlled conditions. These results demonstrate the long-term utility of a reference mapping population and a well-characterized germplasm array for locating and validating genes conferring quantitative and qualitative resistance to multiple pathogens. [ABSTRACT FROM AUTHOR]

A collection of 111 barley landraces from the Fertile Crescent was screened for resistance to barley leaf rust in the field and under controlled conditions. Large variation was observed for disease severity under field conditions. Accessions with high resistance because of hypersensitivity were identified. Also segregation was observed in some accessions, with individual plants showing hypersensitive reactions (IT ≤ 6). Partial resistance due to a reduction of infection in spite of a compatible infection was commonly found (19%). Resistance of 12 accessions selected for their low disease severity and high IT, was shown to be due to a prolonged latency period and increased percentage of early aborted colonies not associated with host cell necrosis. A high correlation was observed between the microscopic and macroscopic components of partial resistance. [ABSTRACT FROM AUTHOR]

The resistance of spring barley varieties to powdery mildew, leaf rust, leaf scald and net blotch was characterized by using results from inoculated small-plot nurseries and larger survey plots subject to natural infection. The experiments were conducted in different environments. Both trial types often yielded complementary results with respect to the ranking of varieties suggesting that a recommended variety characterization should include both naturally infected survey-type trials and nursery trials in which the most relevant pathogen isolates and/or isolate mixtures or populations are used for inoculation. Average and median values of the diseased leaf area of a variety were highly correlated with each other and with the ‘genotype main effect’ determined by joint regression analysis, whereas maximum diseased leaf area was poorly correlated with them. Statistics based on absolute disease severity values were highly correlated with the corresponding statistics derived from relative values. It is suggested that one should use at least two parameters to characterize the disease resistance of a variety, a parameter indicating the overall resistance level and a parameter indicating the potential susceptibility and/or resistance instability of a variety. For practical purposes, the genotype median and maximum, respectively, may represent these, although statistically more appropriate parameters do exist. [ABSTRACT FROM AUTHOR]

AbstractLeaf rust of barley, caused by Puccinia hordei Otth, is an important foliar disease in most temperate regions of the world. Sixteen major leaf rust resistance (Rph) genes have been described from barley, but only a few have been mapped. The leaf rust resistance gene Rph7 was first described from the cultivar ‘Cebada Capa’ and has proven effective in Europe. Previously mapped restriction fragment length polymorphism (RFLP) markers have been used to determine the precise location of this gene in the barley genome. From the genetic analysis of a ‘Bowman’/‘Cebada Capa’ cross, Rph7 was mapped to the end of chromosome 3HS, 1.3 recombination units distal to the RFLP marker cMWG691. A codominant cleaved amplified polymorphic site (CAPS) marker was developed by exploiting allele-specific sequence information of the cMWG691 site and adjacent fragments of genomic DNA. Based on the large amount of polymorphism present in this region, the CAPS marker may be useful for the marker-assisted selection of Rph7 in most diverse genetic backgrounds. [ABSTRACT FROM AUTHOR]

Vast collections of barley germplasm have been established and conserved in various global gene banks. These collections hold tremendous genetic diversity for resistance genes to Puccinia hordei, a causal agent of barley leaf rust. This study was undertaken to discover, characterize and postulate the known Rph genes (resistance to Puccinia hordei) and identify novel sources of ASR (all-stage resistance) and APR (adult plant resistance) to P. hordei. A core set of 315 barley lines were rust-tested as seedlings for their response to eight Australian pathotypes of P. hordei and genotyped with molecular markers linked to the known characterised ASR and APR genes. These tests led to the postulation of ASR leaf rust resistance genes Rph1, Rph2, Rph3, Rph9.am, Rph12, Rph15, Rph19 and Rph25 singly or in combination. Field tests revealed that the vast majority of lines (84%) carried APR. Genotyping of the APR-carrying lines with markers bPb-0837, Ebmac0603 and sun43-44 identified lines that likely carry the known APR genes Rph20, Rph23 and Rph24 singly or in combination. Thirty-nine per cent of the lines were negative for all the three markers and were thus postulated to carry uncharacterized APR. The sources of resistance identified in this study provide a valuable resource to breeders for further utilization and diversifying the genetic basis of leaf rust resistance in barley. [ABSTRACT FROM AUTHOR]

Eighty-three third backcross lines which comprise a set of near isogenic lines (NIL's) of the barley cultivar 'Clipper' but each carrying a different chromosoma' segment from Hordeum spontaneum, marked with a distinct isozyme, were tested for resistance to three races of the barley leaf rust pathogen (Puccinia hordei). Fourteen lines showed resistance to at least one race and three showed resistance to all three races. The resistance in two of these lines was controlled by separate, single partially dominant genes. In one case the resistance gene named Rph10 was on chromosome 3 and linked (r = 0.15 ± 0.05) with the isozyme locus Est2. In the second case, the gene (Rph11) was on barley chromosome 6 and linked (r = 0.07 ± 0.02) with the isozyme locus Acp3 and (r = 0.11 ± 0.02) with Dip2. [ABSTRACT FROM AUTHOR]

Powdery mildew, net blotch, scald, spot blotch, barley stripe, and leaf rust are important foliar fungal pathogens of barley. Fungal leaf pathogens negatively affect the yield and quality in barley plant. Virulence changes, which can occur in various ways, may render resistant plants to susceptible ones. Factors such as mutation, population size and random genetic drift, gene and genotype flow, reproduction and mating systems, selection imposed by major gene resistance, and quantitative resistance can affect the genetic diversity of the pathogenic fungi. The use of fungicide or disease-resistant barley genotypes is an effective method of disease control. However, the evolutionary potential of pathogens poses a risk to overcome resistance genes in the plant and to neutralize fungicide applications. Factors affecting the genetic diversity of the pathogen fungus may lead to the emergence of more virulent new pathotypes in the population. Understanding the factors affecting pathogen evolution, monitoring pathogen biology, and genetic diversity will help to develop effective control strategies. [ABSTRACT FROM AUTHOR]