Barley Leaf Rust Research Articles

An eQTL Analysis of Partial Resistance to Puccinia hordei in Barley

BackgroundGenetic resistance to barley leaf rust caused by Puccinia hordei involves both R genes and quantitative trait loci. The R genes provide higher but less durable resistance than the quantitative trait loci. Consequently, exploring quantitative or partial resistance has become a favorable alternative for controlling disease. Four quantitative trait loci for partial resistance to leaf rust have been identified in the doubled haploid Steptoe (St)/Morex (Mx) mapping population. Further investigations are required to study the molecular mechanisms underpinning partial resistance and ultimately identify the causal genes.Methodology/Principal FindingsWe explored partial resistance to barley leaf rust using a genetical genomics approach. We recorded RNA transcript abundance corresponding to each probe on a 15K Agilent custom barley microarray in seedlings from St and Mx and 144 doubled haploid lines of the St/Mx population. A total of 1154 and 1037 genes were, respectively, identified as being P. hordei-responsive among the St and Mx and differentially expressed between P. hordei-infected St and Mx. Normalized ratios from 72 distant-pair hybridisations were used to map the genetic determinants of variation in transcript abundance by expression quantitative trait locus (eQTL) mapping generating 15685 eQTL from 9557 genes. Correlation analysis identified 128 genes that were correlated with resistance, of which 89 had eQTL co-locating with the phenotypic quantitative trait loci (pQTL). Transcript abundance in the parents and conservation of synteny with rice allowed us to prioritise six genes as candidates for Rphq11, the pQTL of largest effect, and highlight one, a phospholipid hydroperoxide glutathione peroxidase (HvPHGPx) for detailed analysis.Conclusions/SignificanceThe eQTL approach yielded information that led to the identification of strong candidate genes underlying pQTL for resistance to leaf rust in barley and on the general pathogen response pathway. The dataset will facilitate a systems appraisal of this host-pathogen interaction and, potentially, for other traits measured in this population.

Variation in partial resistance to barley leaf rust (Puccinia hordei) and agronomic characters of Ethiopian landrace lines

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.

The resistance to leaf rust and powdery mildew of recombinant lines of barley (Hordeum vulgare L.) derived from H. vulgare × H. bulbosum crosses

AbstractA 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.

Amplified fragment length polymorphism and virulence polymorphism in Puccinia hordei

Puccinia hordei is the causal agent of barley leaf rust. To study the genetic diversity in P. hordei, 45 isolates with diverse virulence patterns and geographical origins were analyzed using amplified fragment length polymorphism markers. Two pathotypes of Puccinia graminis f. sp. tritici and one isolate of P. graminis f. sp. secalis were included in the analysis for comparison. Six primer-pair combinations of amplified fragment length polymorphism were used and a total of 782 polymorphic markers were generated. Cluster analysis showed that P. graminis f. sp. tritici and P. graminis f. sp. secalis were distinctly different from P. hordei. The P. hordei isolates were clustered into five groups: group I contained a single, rare isolate that was virulent on all resistance genes except Rph13 and Rph15 ; group II contained a single isolate found to be virulent on the resistance gene Rph15 ; group III contained 2 isolates; group IV contained 24 isolates, 11 from the United States and 13 from diverse locations around the world; and group V contained 17 isolates, 7 from California, 7 from other states of United States, and 3 from central Europe. The study revealed that molecular diversity in P. hordei can be associated with virulence, but not well with geographic origin.

Relative Ratio of Mature Pustules: A Simple Method to Assess Partial Resistance of Barley to Puccinia hordei.

In plant breeding and germplasm evaluation, large-scale assessment of quantitative resistance is desirable, but feasible only if a simple and accurate measure is available. In several plant-pathogen systems, latent period (LP) is a parameter that is well correlated with the level of partial resistance observed in field trials. However, measuring LP or relative LP (RLP), i.e., relative to the reference accessions, is laborious. We investigated the value of relative ratio of mature pustules (RRMP, relative to the susceptible control) as a simple and rapid alternative to replace LP estimation in barley to barley leaf rust (Puccinia hordei). A set of 103 F9 recombinant inbred lines (RILs) derived from a cross L94 × Vada was sown in a greenhouse compartment, and was inoculated at the seedling stage with isolate Uppsala or 24, and at the adult plant stage with isolate 24. In demarcated sections of leaves, the number of mature pustules was counted several times after inoculation. The ratio of mature pustules (RMP) and LP50 were calculated to assess RRMP and RLP, respectively, and to identify the quantitative trait loci (QTLs) contributing to the genetic variation. The contrasts in RRMP among accessions were highest when the susceptible reference line had developed 70 to 90% mature orange pustules, the immature infection sites being visible as pale flecks. At this optimal time of observation, the correlation between RRMP and RLP in both the seedling stage and the adult plant stage was highly significant (r = -0.82 ~-0.98). Compared with RLP, RRMP was much easier and simpler to measure and still showed good correspondence with RLP in the identification of QTLs for partial resistance. In another experiment at the seedling stage with 25 barley cultivars and lines inoculated with isolate 1.2.1, the coefficient of correlation between RRMP and RLP was -0.98. Therefore, we conclude that RRMP should have great application potential in breeding programs and germplasm screening and could be used in fundamental studies as well.

Host resistance and fungicide control of leaf rust ( Puccinia hordei) in barley ( Hordeum vulgare) and effects on grain yield and yield components

The effectiveness of varying levels of host resistance in five barley ( Hordeum vulgare L.) genotypes and three fungicide application protocols on the control of leaf rust (caused by Puccinia hordei G. Otth) and losses in grain yield, test weight, and 1000-kernel weight was evaluated in field experiments at two locations over four crop years. Fungicide treatments applied to all barley entries at each location and each year included a non-treated control, a single threshold-based application of triadimefon (140 g a.i. ha −1), and a complete control treatment comprised of multiple applications of triadimefon to emulate a disease-free environment. Leaf rust severity was assessed using the James [1971. A Manual of Assessment Keys for Plant Diseases. Canada Dep. Agric. Publ. 1458. The American Phytopathological Society, St. Paul, MN.] scale (0–25%) at three to four plant growth stages and data were used to calculate mean rust severity (MRS) and area under the disease progress curve (AUDPC). Leaf rust epidemics were severe in 1 (1995) of the 4 years of the study, and the treatment effect on grain yield was significant at one location (Warsaw). The susceptible cv. Wysor had a grain yield loss of 33% and MRS was 9.25% (34.23% in modified Cobb scale) at this location. In 2 (1995 and 1997) of 4 years of study, significant ( P ⩽ 0.05 ) negative correlations were obtained between MRS and grain yield, test weight, and 1000-kernel weight of cv. Wysor at both locations. In the other 2 years (1994 and 1996) when leaf rust epidemics were mild, these correlations were mostly non-significant. In general, fungicide treatment significantly ( P ⩽ 0.05 ) reduced MRS and AUDPC and reduced losses in grain yield, test weight, and 1000-kernel weight for the susceptible and moderately susceptible cultivars compared with the non-treated control. The cv. Starling, possessing adult-plant resistance, did not consistently benefit from fungicide application. There was no benefit from fungicide application for control of leaf rust in the resistant line VA92-42-46. In general, the complete-control fungicide treatment did not result in further significant reduction in leaf rust or losses in grain yield compared to threshold-level fungicide applications.

Barley leaf rust (Puccinia hordei Otth) in three production systems and practices in Ethiopia

To determine the prevalence, incidence and severity of leaf rust (Puccinia hordei) in three different production systems of Ethiopia, 276 barley (Hordeum vulgare) fields from the main rainy season (MRS), residual moisture season (RMS), and short rainy season (SRS) production systems were surveyed during the 2003 and 2004 cropping seasons. Over the 2 years, all the barley fields in RMS, 93% in MRS and 51% in SRS production systems were affected by leaf rust. Mean incidence of leaf rust varied from 34.8% in SRS to 76.4% in RMS and in the same order severity of the disease varied from 5.9 to 15.3%. The mean differences in incidence and severity within the variable classes for the provinces, districts, altitude, fertilizer application, weed density and local cultivar were also high. The independent variables: production systems, provinces, districts, altitude, planting dates, fertilizer application, local cultivar and weed density were significantly associated with high incidence and severity of leaf rust as single predictors in the logistic regression models. However, region and slope of a barley field were not associated with increasing disease intensity. A reduced multiple variable model was fitted using districts, altitudes, fertilizer applications, and weed densities as independent variables. Low rust incidence (⩽50%) and severity (⩽5%) had a high probability of association to Enessie, Agew Midir, Degem and Ankober districts. Incidence of above 50% and severity of above 5% had high probability of association to the RMS production system, Gassera district, and high weed density. In the reduced multiple variable models, province and local cultivar lost importance due to the confounding effect with the districts.

A high-density consensus map of barley to compare the distribution of QTLs for partial resistance to Puccinia hordei and of defence gene homologues

A consensus map of barley was constructed based on three reference doubled haploid (DH) populations and three recombinant inbred line (RIL) populations. Several sets of microsatellites were used as bridge markers in the integration of those populations previously genotyped with RFLP or with AFLP markers. Another set of 61 genic microsatellites was mapped for the first time using a newly developed fluorescent labelling strategy, referred to as A/T labelling. The final map contains 3,258 markers spanning 1,081 centiMorgans (cM) with an average distance between two adjacent loci of 0.33 cM. This is the highest density of markers reported for a barley genetic map to date. The consensus map was divided into 210 BINs of about 5 cM each in which were placed 19 quantitative trait loci (QTL) contributing to the partial resistance to barley leaf rust (Puccinia hordei Otth) in five of the integrated populations. Each parental barley combination segregated for different sets of QTLs, with only few QTLs shared by any pair of cultivars. Defence gene homologues (DGH) were identified by tBlastx homology to known genes involved in the defence of plants against microbial pathogens. Sixty-three DGHs were located into the 210 BINs in order to identify candidate genes responsible for the QTL effects. Eight BINs were co-occupied by a QTL and DGH(s). The positional candidates identified are receptor-like kinase, WIR1 homologues and several defence response genes like peroxidases, superoxide dismutase and thaumatin.

Effect of partial resistance to barley leaf rust, Puccinia hordei, on the yield of three barley cultivars

Three barley cultivars, Shyri, Clipper and Teran, 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.

Mapping multiple disease resistance genes using a barley mapping population evaluated in Peru, Mexico, and the USA

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.

Identification of a new pathotype of Puccinia hordei with virulence for the resistance gene Rph7

Barley leaf rust resistance gene Rph7, derived from barley accession Cebada Capa, is the most effective R-gene for resistance to Puccinia hordei. Virulence for this gene was known in the USA, Israel and Morocco but not yet in Europe. We found an unexpected leaf rust infection in the field at Cordoba, Spain in 2004 on Rph7 carrying lines. This virulence for Rph7 was confirmed in growth chamber experiments, being the first report of Rph7 virulence in European populations of P. hordei. A collection of 680 barley accessions was screened for resistance against this new isolate. Twelve accessions showed segregation with individual plants showing resistance based on hypersensitivity (low infection type). These individual resistant plants were selected and grown in the greenhouse to obtain seeds.

Search for partial resistance against Puccinia hordei in barley landraces from the Fertile Crescent

AbstractA 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.

Virulence spectrum of Puccinia hordei in barley production systems in Ethiopia

Barley leaf rust caused by Puccinia hordei is an important disease of barley in Ethiopia. In the 2003 and 2004 cropping seasons, surveys of P. hordei were conducted on fields in the main rainy, residual moisture and short rainy season‐barley production systems. A total of 381 isolates were analysed on 12 barley differential hosts carrying different Rph resistance genes (Rph1–Rph12). Based on infection phenotypes on leaf rust (Rph) resistance genes, seven pathotypes were identified, namely ETPh7611, ETPh7631, ETPh6611, ETPh7651, ETPh7671, ETPh7653 and ETPh7633, with frequencies of 63·0, 21·5, 6·8, 2·9, 2·6, 2·1 and 1·2%, respectively. ETPh7611 and ETPh7631 were the most common pathotypes found in all the surveyed areas of the three production systems. ETPh7653 was found in the small rainy season production system only. ETPh7671, ETPh7653 and ETPh7633 were the most virulent, but the least frequent, pathotypes. All isolates were virulent on resistance genes Rph1, Rph4, Rph8, Rph9, Rph11 and Rph12. Virulence against Rph3 and Rph7 was absent. Genes Rph2, Rph6+2, Rph5 and Rph10 were effective against 96·3, 88·9, 65 and 2·4% of the rust isolates tested, respectively.

High-resolution mapping of the barley leaf rust resistance gene Rph5 using barley expressed sequence tags (ESTs) and synteny with rice

The rapidly growing expressed sequence tag (EST) resources of species representing the Poacea family and availability of comprehensive sequence information for the rice (Oryza sativa) genome create an excellent opportunity for comparative genome analysis. Extensive synteny between rice chromosome 1 and barley (Hordeum vulgare L.) chromosome 3 has proven extremely useful for saturation mapping of chromosomal regions containing target genes of large-genome barley with conserved orthologous genes from the syntenic regions of the rice genome. Rph5 is a gene conferring resistance to the barley leaf rust pathogen Puccinia hordei. It was mapped to chromosome 3HS, which is syntenic with rice chromosome 1S. The objective of this study was to increase marker density within the sub-centimorgan region around Rph5, using sequence-tagged site (STS) markers that were developed based on barley ESTs syntenic to the phage (P1)-derived artificial chromosome (PAC) clones comprising the distal region of rice chromosome 1S. Five rice PAC clones were used as queries in a blastn search to screen 375,187 barley ESTs. Ninety-four non-redundant EST sequences were identified from the EST database and used as templates to design 174 pairs of primer combinations. As a result, 9 barley EST-based STS markers were incorporated into the 'Bowman' x 'Magnif 102' high-resolution map of the Rph5 region. More importantly, six markers, including five EST-derived STS sequences, were found to co-segregate with Rph5. The results of this study demonstrate the usefulness of rice genomic resources for efficient deployment of barley ESTs for marker saturation of targeted barley genomic regions.

Resistance to barley yellow dwarf virus, powdery mildew and leaf rust in wheat x Thinopyrum backcrosses

Wheat (Triticumaestivum) relatives are sources of useful genes for disease resistance. Chromosomally segregating populations of intergeneric hybrids between wheat and its distantly related species provide opportunity to study and introgress multiple disease resistance. While introgressing resistance to barley yellow dwarf virus (BYDV) from Thinopyrum into wheat, which is susceptible to BYDV, we scored powdery mildew (Erysiphaegraminis) and leaf rust (Pucciniatriticina) resistance, and chromosome numbers in second and third backcrosses (BC2 and BC3) of intergeneric hybrids of wheat with Thinopyrum ponticum and Thinopyrumintermedium. The frequency of multiple resistance to all the three diseases was low or became low when selection was applied for BYDV resistance and low chromosome numbers. Selection for fewer alien chromosomes while maintaining BYDV resistance was more effective in wheat x T. intermedium than in the wheat x T. ponticum cross. Mean chromosome numbers were significantly different in BC3 generation between BYDV resistant and susceptible plants in both crosses. Significant negative correlations between chromosome numbers and enzyme-linked immunosorbent assay (ELISA) values showed that as the critical Thinopyrum chromosome(s) were eliminated, susceptibility to BYDV increased. Results indicated that it is unlikely that genes for full resistance to all three diseases can be transferred simultaneously from Thinopyrum to wheat.

Aberrant mRNA processing of the maize Rp1-D rust resistance gene in wheat and barley.

The maize Rp1-D gene confers race-specific resistance against Puccinia sorghi (common leaf rust) isolates containing a corresponding avrRp1-D avirulence gene. An Rp1-D genomic clone and a similar Rp1-D transgene regulated by the maize ubiquitin promoter were transformed independently into susceptible maize lines and shown to confer Rp1-D resistance, demonstrating that this resistance can be transferred as a single gene. Transfer of these functional transgenes into wheat and barley did not result in novel resistances when these plants were challenged with isolates of wheat stem rust (P. graminis), wheat leaf rust (P. triticina), or barley leaf rust (P. hordei). Regardless of the promoter employed, low levels of gene expression were observed. When constitutive promoters were used for transgene expression, a majority of Rp1-D transcripts were truncated in the nucleotide binding site-encoding region by premature polyadenylation. This aberrant mRNA processing was unrelated to gene function because an inactive version of the gene also generated such transcripts. These data demonstrate that resistance gene transfer between species may not be limited only by divergence of signaling effector molecules and pathogen avirulence ligands, but potentially also by more fundamental gene expression and transcript processing limitations.

Effect of Host Plant Resistance on Haustorium Formation in Cereal Rust Fungi

AbstractHaustoria of Puccinia triticina (wheat leaf rust fungus) and P. hordei (barley leaf rust fungus) were isolated from susceptible and partially resistant wheat lines, and susceptible, hypersensitive and partially resistant barley lines. Haustoria were counted and measured. The size of haustoria was similar in the partially resistant and susceptible genotypes but haustoria were smaller in the hypersensitive barley line L94+Pa7. The number of haustoria was reduced in both partially and hypersensitive lines when compared with susceptible ones. Therefore it seems that the reduction in the number of haustoria is a consequence of the resistance that can be attributable either to early abortion of infection units or reduced colony growth. The reduction of the number of haustoria was more pronounced in the adult plant stage.

Abnormal germling development by brown rust and powdery mildew on cer barley mutants.

The barley leaf rust fungus forms appressoria over host leaf stomata and penetrates via the stomatal pore. High levels of avoidance to leaf rust fungi have been described in some wild accessions of Hordeum species where a prominent wax layer on the stomata inhibits triggering of fungal appressorium differentiation. Leaf rust avoidance has not yet been found in H. vulgare. Since cuticular leaf waxes are implicated in the avoidance trait, we screened 27 eceriferum (cer) mutant lines of H. vulgare for avoidance to barley leaf rust. These mutations affect leaf waxes. Reduction in numbers of germ tubes forming appressoria over stomata was found in some lines, but the greatest reduction (ca 30%) was less than previously found in wild barley spp. or in an accession of H. chilense used here as a check. In one line (cer-zh654), avoidance was due to a combination of factors. Firstly, fewer germ tubes oriented towards stomata and so failed to contact them. Secondly, some germ tubes that encountered stomata did not form appressoria but over-grew them. In this line, therefore, the fungus tended to fail both to locate and to respond to stomata. The appressoria of barley powdery mildew form on leaf epidermal cells that they penetrate directly. On certain cer lines, a proportion of germlings of the barley powdery mildew fungus developed abnormally, suggesting that germlings failed to recognise and/or respond to the leaf surface waxes on these mutants.

QTL mapping provides evidence for lack of association of the avoidance of leaf rust in Hordeum chilense with stomata density.

In cereals, rust fungi are among the most harmful pathogens. Breeders usually rely on short-lived hypersensitivity resistance. As an alternative, "avoidance" may be a more durable defence mechanism to protect plants to rust fungi. In Hordeum chilense avoidance is based on extensive wax covering of stomata, which interferes with the induction of appressorium formation by the rust fungi. High avoidance levels are associated with a higher stoma density on the abaxial leaf epidermis. The avoidance level was assessed as the percentage of germ tube/stoma encounters that did not result in appressorium differentiation by Puccinia hordei, the barley leaf rust fungus. One hundred F(2) individuals from the cross between two H. chilense accessions with contrasting levels of avoidance showed a continuous distribution for avoidance of the rust fungus and for stoma density, indicating quantitative inheritance of the traits. No significant correlation was found between avoidance and stoma density in the segregating F(2) population. In order to map quantitative trait loci (QTLs) for both traits, an improved molecular marker linkage map was constructed, based on the F(2) population. The resulting linkage map spanned 620 cM and featured a total of 437 AFLP markers, thirteen RFLPs, four SCARs, nine SSRs, one STS and two seed storage protein markers. It consisted of seven long and two shorter linkage groups, and was estimated to cover 81% of the H. chilense genome. Restricted multiple interval mapping identified two QTLs for avoidance and three QTLs for stoma density in the abaxial leaf surface. The QTLs for avoidance were mapped on chromosome 3 and 5; those for stoma density on chromosomes 1, 3 and 7. Only the two QTLs regions located on chromosome 3 (one for avoidance and the other for stoma density) overlapped. The wild barley H. chilense has a high crossability with other members of the Triticeae tribe. The knowledge on the location of the QTLs responsible for the avoidance trait is a prerequisite to transfer this favourable agronomic trait from H. chilense to cultivated cereal genomes.

Mapping genes for resistance to Puccinia hordei in barley

Six doubled haploid barley populations (Alexis × Sloop, Chebec × Harrington, Arapiles × Franklin, Patty × Tallon, Tallon × Kaputar, and Sloop × Halcyon) and a recombinant inbred population (WI2875-1 × Alexis) were assessed for response to selected pathotypes of the barley leaf rust pathogen, Puccinia hordei, at the seedling growth stage. Resistance genes were postulated for the parents of each population based on their reaction to selected pathotypes. In most cases, the resistance genes postulated in the cultivars were validated by QTL mapping analyses of the progeny populations. The resistance genes detected and mapped were Rph2, Rph3, Rph4, Rph12, and Rph19. The chromosomal locations of these 5 genes were consistent with previous reports, with Rph2 mapping near to the centromere on the short arm of chromosome 5H, Rph4 mapping to chromosome 1H, Rph12 mapping to the long arm of chromosome 5H, and Rph3 and Rph19 mapping ~30 cM apart on the long arm of chromosome 7H.