A biological and molecular characterization of some Egyptian barley genotypes which are resistant to net blotch disease

A survey for resistance against net blotch disease (caused by Pyrenophora teres) was performed on some Egyptian barley landraces and some selected resistance and susceptible standard German barley genotypes. The results indicated that most of the Egyptian barley landraces are extremely resistant to the disease. Molecular analysis using RAPD and AFLP showed unique banding profiles for the different genotypes, and specific AFLP markers for the Egyptian genotypes were identified. The effectiveness of RAPD and AFLP for identifying different barley genotypes of different origins and with different reactions against P. teres was discussed. The results of the biological evaluation and molecular characterization done in this study can be seen as the starting point needed to identify the valuable net blotch resistant Egyptian barley germplasm at both the phenotype and genotype levels and draw the attention of breeders and banks of natural plant genetic resources towards this valuable yet neglected germplasm.     

Seedling and adult stage resistance to net form of net blotch (NFNB) in spring barley and stability of adult stage resistance to NFNB in Morocco

This study was conducted to identify stable resistance to net form of net blotch (NFNB) in spring barley in Moroccan environments. Seedling resistance to NFNB was evaluated by inoculating 336 barley genotypes with two NFNB isolates LDNH04Ptt-19 and TD-10 in the greenhouse. These genotypes were evaluated for adult plant resistance to NFNB under seven environments in Morocco in 2015 and 2016. The disease severity was estimated at GS 77–87 on barley leaves using a double-digit scale. To investigate stability of resistance, 149 barley genotypes were subjected to AMMI analysis. At the seedling stage, differential responses of barley genotypes to different NFNB isolates were identified, whereas genotypes had variable stability to NFNB resistance at the adult stages. Five genotypes, AM-68, AM-95, AM-250, AM-267 and AM-322, were resistant to both NFNB isolates at the seedling stage. There were significant (p < .001) effects of genotype (G) and G × E interaction on NFNB severity for barley genotypes at the adult stage. The principal components, IPCA1 and IPCA2, accounted for 48.4% and 18.7% variation for NFNB severity, respectively. The AMMI stability values (ASVs) ranged from 0.01 to 15.5, and fifty-nine barley genotypes had stable responses (ASV ≤ 0.05) across all seven environments. Specifically, two stable genotypes, AM-187 and AM-244, had lower mean NFNB severities across all environments, suggesting a quantitative resistance in these genotypes. Divergent environmental responses of NFNB severity were measured in Sidi El Ayedi 2015 and Sidi Allal Tazi 2016, suggesting that these environments may be suitable to capture resistance to diverse pathotypes. These stable genotypes are valuable resources for introgression of both qualitative resistance and quantitative resistance to NFNB in future.     

Identification and chromosomal location of major genes for resistance to Pyrenophora teres in a doubled-haploid barley population.

Net blotch, caused by Pyrenophora teres, is one of the most economically important diseases of barley worldwide. Here, we used a barley doubled-haploid population derived from the lines SM89010 and Q21861 to identify major quantitative trait loci (QTLs) associated with seedling resistance to P. teres f. teres (net-type net blotch (NTNB)) and P. teres f. maculata (spot-type net blotch (STNB)). A map consisting of simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers was used to identify chromosome locations of resistance loci. Major QTLs for NTNB and STNB resistance were located on chromosomes 6H and 4H, respectively. The 6H locus (NTNB) accounted for as much as 89% of the disease variation, whereas the 4H locus (STNB resistance) accounted for 64%. The markers closely linked to the resistance gene loci will be useful for marker-assisted selection.     

Pyrenophora teres: profile of an increasingly damaging barley pathogen

Pyrenophora teres, causal agent of net blotch of barley, exists in two forms, designated P. teres f. teres and P. teres f. maculata, which induce net form net blotch (NFNB) and spot form net blotch (SFNB), respectively. Significantly more work has been performed on the net form than on the spot form although recent activity in spot form research has increased because of epidemics of SFNB in barley-producing regions. Genetic studies have demonstrated that NFNB resistance in barley is present in both dominant and recessive forms, and that resistance/susceptibility to both forms can be conferred by major genes, although minor quantitative trait loci have also been identified. Early work on the virulence of the pathogen showed toxin effector production to be important in disease induction by both forms of pathogen. Since then, several laboratories have investigated effectors of virulence and avirulence, and both forms are complex in their interaction with the host. Here, we assemble recent information from the literature that describes both forms of this important pathogen and includes reports describing the host-pathogen interaction with barley. We also include preliminary findings from a genome sequence survey. TAXONOMY: Pyrenophora teres Drechs. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Dothideomycete; Order Pleosporales; Family Pleosporaceae; Genus Pyrenophora, form teres and form maculata. IDENTIFICATION: To date, no clear morphological or life cycle differences between the two forms of P. teres have been identified, and therefore they are described collectively. Towards the end of the growing season, the fungus produces dark, globosely shaped pseudothecia, about 1-2mm in diameter, on barley. Ascospores measuring 18-28μm × 43-61μm are light brown and ellipsoidal and often have three to four transverse septa and one or two longitudinal septa in the median cells. Conidiophores usually arise singly or in groups of two or three and are lightly swollen at the base. Conidia measuring 30-174μm × 15-23μm are smoothly cylindrical and straight, round at both ends, subhyaline to yellowish brown, often with four to six pseudosepta. Morphologically, P. teres f. teres and P. teres f. maculata are indistinguishable. HOST RANGE: Comprehensive work on the host range of P. teres f. teres has been performed; however, little information on the host range of P. teres f. maculata is available. Hordeum vulgare and H. vulgare ssp. spontaneum are considered to be the primary hosts for P. teres. However, natural infection by P. teres has been observed in other wild Hordeum species and related species from the genera Bromus, Avena and Triticum, including H. marinum, H. murinum, H. brachyantherum, H. distichon, H. hystrix, B. diandrus, A. fatua, A. sativa and T. aestivum (Shipton et al., 1973, Rev. Plant Pathol. 52:269-290). In artificial inoculation experiments under field conditions, P. teres f. teres has been shown to infect a wide range of gramineous species in the genera Agropyron, Brachypodium, Elymus, Cynodon, Deschampsia, Hordelymus and Stipa (Brown et al., 1993, Plant Dis. 77:942-947). Additionally, 43 gramineous species were used in a growth chamber study and at least one of the P. teres f. teres isolates used was able to infect 28 of the 43 species tested. However, of these 28 species, 14 exhibited weak type 1 or 2 reactions on the NFNB 1-10 scale (Tekauz, 1985). These reaction types are small pin-point lesions and could possibly be interpreted as nonhost reactions. In addition, the P. teres f. teres host range was investigated under field conditions by artificially inoculating 95 gramineous species with naturally infected barley straw. Pyrenophora teres f. teres was re-isolated from 65 of the species when infected leaves of adult plants were incubated on nutrient agar plates; however, other than Hordeum species, only two of the 65 host species exhibited moderately susceptible or susceptible field reaction types, with most species showing small dark necrotic lesions indicative of a highly resistant response to P. teres f. teres. Although these wild species have the potential to be alternative hosts, the high level of resistance identified for most of the species makes their role as a source of primary inoculum questionable. DISEASE SYMPTOMS: Two types of symptom are caused by P. teres. These are net-type lesions caused by P. teres f. teres and spot-type lesions caused by P. teres f. maculata. The net-like symptom, for which the disease was originally named, has characteristic narrow, dark-brown, longitudinal and transverse striations on infected leaves. The spot form symptom consists of dark-brown, circular to elliptical lesions surrounded by a chlorotic or necrotic halo of varying width.     

Mapping of major spot-type and net-type net-blotch resistance genes in the Ethiopian barley line CI 9819.

Net blotch of barley (Hordeum vulgare L.), caused by the fungal phytopathogen Pyrenophora teres Drechs. f. teres Smedeg., constitutes one of the most serious constraints to barley production worldwide. Two forms of the disease, the net form, caused by P. teres f. teres, and the spot form, caused by P. teres f. maculata, are differentiated by the type of symptoms on leaves. Several barley lines with major gene resistance to net blotch have been identified. Earlier, one of these was mapped in the Rolfi x CI 9819 cross to barley chromosome 6H, using a mixture of 4 Finnish isolates of P. teres f. teres. In this study, we used the same barley progeny to map resistance to 4 spot-type isolates and 4 net-type isolates of P. teres. With all net-type isolates, a major resistance gene was located on chromosome 6H, in the same position as described previously, explaining up to 88% of the phenotypic variation in infection response in the progeny. We designate this gene Rpt5. Several minor resistance genes were located on chromosomes 1H, 2H, 3H, 5H, and 7H. These minor genes were not genuinely isolate-specific, but their effect varied among isolates and experiments. When the spot-type isolates were used for infection, a major isolate-specific resistance gene was located on chromosome 5H, close to microsatellite marker HVLEU, explaining up to 84% of the phenotypic variation in infection response in the progeny. We designate this gene Rpt6. No minor gene effects were detected in spot-type isolates. The Ethiopian 2-rowed barley line CI 9819 thus carries at least 2 independent major genes for net-blotch resistance: Rpt5, active against net-type isolates; and Rpt6, active against specific spot-type isolates.     

Evolution of three Pyrenophora cereal pathogens: Recent divergence, speciation and evolution of non-coding DNA

Three of the most important fungal pathogens of cereals are Pyrenophora tritici-repentis, the cause of tan spot on wheat, and Pyrenophora teres f. teres and Pyrenophora teres f. maculata, the cause of spot form and net form of net blotch on barley, respectively. Orthologous intergenic regions were used to examine the genetic relationships and divergence times between these pathogens. Mean divergence times were calculated at 519kya (±30) between P. teresf. teres and P. teresf. maculata, while P. tritici-repentis diverged from both Pyrenophora teresforms 8.04Mya (±138ky). Individual intergenic regions showed a consistent pattern of co-divergence of the P. teresforms from P. tritici-repentis, with the pattern supported by phylogenetic analysis of conserved genes. Differences in calculated divergence times between individual intergenic regions suggested that they are not entirely under neutral selection, a phenomenon shared with higher Eukaryotes. P. tritici-repentis regions varied in divergence time approximately 5-12Mya from the P. teres lineage, compared to the separation of wheat and barley some 12Mya, while the P. teresf. teres and P. teresf. maculata intergenic region divergences correspond to the middle Pleistocene. The data suggest there is no correlation between the divergence of these pathogens the domestication of wheat and barley, and show P. teresf. teres and P. teresf. maculata are closely related but autonomous. The results are discussed in the context of speciation and the evolution of intergenic regions.     

Interaction between Rhynchosporium secalis and Pyrenophora teres in the Field and Identification of Genotypes with Double Resistance in a Doubled-haploid Barley Population

Net blotch [Pyrenophora teres (Died.) Drechsl.] and scald [Rhynchosporium secalis (Oudem.) J.J. Davis] are the two most important foliar diseases of barley (Hordeum vulgare L.) in Tunisia. The use of cultivars with double resistance is the most effective method in controlling both diseases. A doubled‐haploid barley population derived from Tunisian cultivars was evaluated to both net blotch and scald during two growing seasons in the field. Mass disease index (MDI), area under the disease progress curve (AUDPC) and apparent infection type (r) were used to assess disease reaction. MDI of net blotch and scald reached up to 65% and 90% respectively. Least significant difference (LSD) test and comparison of the reaction of the doubled haploid (DH) lines to the overall population mean value were efficient in identifying lines with double resistance to both diseases. From the 59 DH lines screened, lines 21, 33, 37, 46 and 47 showed the best level of adult plant resistance to both diseases and may be used in a breeding program for diseases resistance. Interactions between R. secalis and P. teres were investigated at the level of the whole plant under variable epidemic conditions. Under low epidemic conditions, net blotch and scald developments were usually independent, but positively associated for tolerant lines for both diseases. Under high epidemic conditions, competition effects were obtained for susceptible and resistant genotypes. This competition seems to be an exploitation competition that is associated with decreasing resource availability as it occurs only with high levels of infestation or/and when susceptible lines are infected. This study demonstrates the variability of net blotch and scald interaction with epiphytotic conditions and group of resistance.     

Mapping quantitative trait loci associated with barley net blotch resistance

Net blotch of barley, caused by Pyrenophora teres Drechs., is an important foliar disease worldwide. Deployment of resistant cultivars is the most economic and eco-friendly control method. This report describes mapping of quantitative trait loci (QTL) associated with net blotch resistance in a doubled-haploid (DH) barley population using diversity arrays technology (DArT) markers. One hundred and fifty DH lines from the cross CDC Dolly (susceptible)/TR251 (resistant) were screened as seedlings in controlled environments with net-form net blotch (NFNB) isolates WRS858 and WRS1607 and spot-form net blotch (SFNB) isolate WRS857. The population was also screened at the adult-plant stage for NFNB resistance in the field in 2005 and 2006. A high-density genetic linkage map of 90 DH lines was constructed using 457 DArT and 11 SSR markers. A major NFNB seedling resistance QTL, designated QRpt6, was mapped to chromosome 6H for isolates WRS858 and WRS1607. QRpt6 was associated with adult-plant resistance in the 2005 and 2006 field trials. Additional QTL for NFNB seedling resistance to the more virulent isolate WRS858 were identified on chromosomes 2H, 4H, and 5H. A seedling resistance QTL (QRpts4) for the SFNB isolate WRS857 was detected on chromosome 4H as was a significant QTL (QRpt7) on chromosome 7H. Three QTL (QRpt6, QRpts4, QRpt7) were associated with resistance to both net blotch forms and lines with one or more of these demonstrated improved resistance. Simple sequence repeat (SSR) markers tightly linked to QRpt6 and QRpts4 were identified and validated in an unrelated barley population. The major 6H QTL, QRpt6, may provide adequate NFNB field resistance in western Canada and could be routinely selected for using molecular markers in a practical breeding program.     

Identification and mapping of net form of net blotch resistance in South African barley

Net form of net blotch (NFNB) caused by the fungus Pyrenophora teres f. teres is an economically important foliar disease of barley (Hordeum vulgare) in southern and eastern Africa. Little attention has been given to disease resistance breeding, and knowledge about the presence of NFNB resistance in breeding lines is limited. Deploying resistance into varieties used in this region is important for future control of the disease. We have identified NFNB disease resistance in existing South African breeders’ lines and have mapped the resistance in line UVC8. Six different trials, three conducted in South Africa and another three in Australia, were used to identify resistance QTL. A major QTL was identified on chromosome 6H having a LOD score of 40.5 and 55% of the phenotypic variance explained. Kompetitive Allele Specific PCR (KASP?) markers were designed for this QTL region. These and microsatellite markers can now be used to routinely select for NFNB resistance.     

Quantification of Pyrenophora teres in infected barley leaves using real-time PCR

Net blotch is a barley foliar disease caused by two forms of Pyrenophora teres: Pyrenophora teres f. teres (PTT) and Pyrenophora teres f. maculata (PTM). To monitor and quantify their occurrence during the growing season, diagnostic system based on real-time PCR was developed. TaqMan MGB (Minor Groove Binder) primers and probes were designed that showed high specificity for each of the two forms of P. teres. As a host plant internal standard, TaqMan MGB primers and probe based on RacB gene sequence were designed. The method was optimised on pure fungal DNA and on plasmid standard dilutions. Quantification was accomplished by comparing Ct values of unknown samples with those obtained from plasmid standard dilutions. The assay detects down to five gene copies per reaction. It is able to produce reliable quantitative data over a range of six orders of magnitude. The developed assay was used to differentiate and quantify both forms of P. teres in infected barley leaves. Correlation R(2)=0.52 was obtained between the Ct values and size of symptoms areas in early stage of infection. Application of the TaqMan MGB technology to leaf samples collected in 20 barley varieties in the region Kromeriz during the growing season of 2003 and 2004 revealed that P. teres f. teres predominated in these 2 years. The developed method is an important tool to quantify and monitor the dynamics of the two forms of P. teres during the growing season.     

Population genetic structure of <Emphasis Type="Italic">Pyrenophora teres</Emphasis>Drechs. the causal agent of net blotch in Sardinian landraces of barley (<Emphasis Type="Italic">Hordeum vulgare L.</Emphasis>)

Monoconidial cultures of Pyrenophora teres, the causal agent of barley net blotch, were isolated from leaves collected from six populations of the barley landrace "S'orgiu sardu" growing in five agro-ecological areas of Sardinia, Italy, and genotyped using AFLPs. The 150 isolates were from lesions of either the "net form" (P. teres f. sp. teres) or the "spot form" (P. teres f. sp. maculata) of the disease. Of 121 AFLP markers, 42%, were polymorphic. Cluster analysis resolved the isolates into two strongly divergent groups (F(ST) = 0.79), corresponding to the net (45% of the isolates) and the spot (55% of the isolates) forms (designated the NFR and SFR groups, respectively). The absence of intermediate genotypes and the low number of shared markers between the two groups indicated that hybridization between the two formae is rare or absent under the field condition of Sardinia. Five of the barley populations hosted both forms but in different proportions. The SFR populations were similar in overall polymorphism to the NFR populations. However, compared to the SFR form, the NFR occurred in all fields sampled and showed a higher population divergence (F(ST) = 0.43 versus F(ST) = 0.09 with all isolates; F(ST) = 0.37 versus F(ST) = 0.06 with clone corrected samples) probably due to a lower migration rate. AFLP fingerprints resolved 117 distinct genotypes among the 150 isolates sampled (78%), 87% in SFR and 68% in NFR isolates. Although the absolute numbers may be a function of the number of AFLP markers assayed, the relative difference suggests that clonality is more prevalent among the NFR isolates (with 11 of 46 haplotypes observed more than once), compared with SFR isolates (7 of 71 haplotypes). Both digenic and multilocus linkage disequilibrium analyses suggested that sexual reproduction occurs at significant levels within the NFR and SFR populations, and that the relative contribution of sexual and asexual reproduction varies among different environments.     

Genetic control of virulence of Pyrenophora teres drechs, the causative agent of net blotch in barley

The genetic control of virulence was studied in four isolates of the fungus Pyrenophora teres f. teres, originating from various geographic regions in experiments with nine barley accessions, possessing known resistance genes. Experiments were performed with the ascospore progeny of two crosses. The results of segregation for virulence in the progeny of direct crosses were confirmed by analysis of backcrosses and sib crosses. One to four genes for avirulence toward various barley genotypes were found in the isolates under study. It is suggested that dominant suppressor genes are involved in the genetic control of avirulence toward four barley genotypes.     

Identification of quantitative trait loci associated with resistance to net form net blotch in a collection of Nordic barley germplasm

Key message

Association mapping of resistance to Pyrenophora teres f. teres in a collection of Nordic barley germplasm at different developmental stages revealed 13 quantitative loci with mostly small effects.

Abstract

Net blotch, caused by the necrotrophic fungus Pyrenophora teres, is one of the major diseases in barley in Norway causing quantitative and qualitative yield losses. Resistance in Norwegian cultivars and germplasm is generally insufficient and resistance sources have not been extensively explored yet. In this study, we mapped quantitative trait loci (QTL) associated with resistance to net blotch in Nordic germplasm. We evaluated a collection of 209 mostly Nordic spring barley lines for reactions to net form net blotch (NFNB; Pyrenophora teres f. teres) in inoculations with three single conidia isolates at the seedling stage and in inoculated field trials at the adult stage in 4 years. Using 5669 SNP markers genotyped with the Illumina iSelect 9k Barley SNP Chip and a mixed linear model accounting for population structure and kinship, we found a total of 35 significant marker-trait associations for net blotch resistance, corresponding to 13 QTL, on all chromosomes. Out of these QTL, seven conferred resistance only in adult plants and four were only detectable in seedlings. Two QTL on chromosomes 3H and 6H were significant during both seedling inoculations and adult stage field trials. These are promising candidates for breeding programs using marker-assisted selection strategies. The results elucidate the genetic background of NFNB resistance in Nordic germplasm and suggest that NB resistance is conferred by a number of genes each with small-to-moderate effects, making it necessary to pyramid these genes to achieve sufficient levels of resistance.

     

A new technique for monoconidial culture of the most aggressive isolate in a given population of Bipolaris sorokiniana, cause of foliar spot blotch in wheat and barley

We developed a new technique for monoconidial culture of the most aggressive isolate in a given population of Bipolaris sorokiniana, to facilitate the evaluation of spot blotch resistance in wheat and barley. Blotched portions of infected barley leaves were placed on a glass slide in a moist chamber for production of conidia by associated fungal hyphae. Conidia were collected separately and grown on water agar discs. Individual water agar discs having conidium growth were inoculated on barley leaves. The conidium producing the earliest symptom with the largest lesion was considered most aggressive. This lesion was incubated in a moist chamber and the conidial offspring were tested for pathogenicity. When a uniform infection was observed, a small piece of the lesion was cut using a sterilized scalpel, surface sterilized with NaOCl, and inoculated in the centre of Petri dishes containing potato dextrose agar medium. The inoculated Petri dishes were incubated at 25 ± 1 °C to yield monoconidial cultures of the most aggressive isolate. Variability in symptom expression caused by the most aggressive isolate of a given population was much less than variability in symptom expression caused by all isolates collectively. The techniques will be useful for plant pathologists and breeders in screening for spot blotch resistance in wheat and barley.     

Surveys of diseases of winter barley in England and Wales, 1981–1991

Samples from 200–400 randomly selected winter barley crops were taken annually at growth stage 71–73 from 1981 to 1991, with the exception of 1984 and 1985. The number of samples from each region was proportional to the area of barley growth in each region. The percentage of the area of the top two leaves affected by diseases and the severity of stem base diseases were recorded. Mildew (Erysiphe graminis) was the most widespread of the foliar diseases and in three years (1982, 1986 and 1991) was also the most severe. Rhynchosporium (Rhynchosporium secalis), net blotch (Pyrenophora teres) and brown rust (Puc-cinia hordei) were also prevalent in some years. Of the stem base diseases, fusarium was often the most widespread. Eyespot (Pseudocercosporella her-potrichoides) severity varied widely from year to year ranging from 1.2% of stems affected by moderate or severe symptoms in 1982 to 24.1% in 1988. There were regional differences in the severity of mildew, rhynchosporium, brown rust, halo spot (Selenophoma donacis) and eyespot. Cultivar resistance affected disease severity and previous cropping affected eyespot and less frequently mildew, rhynchosporium and net blotch. Eyespot, and to a lesser extent, sharp eyespot, were less severe in late- than in early-sown crops. The percentage of crops treated with a fungicidal spray increased from 72% in 1981 to 95% in 1991. The use of benzimidazole fungicides for the control of eyespot declined in response to the development of resistance, and more recently the use of prochlo-raz also declined. Broad spectrum DMI fungicides were widely used, and the use of morpholines to improve mildew control increased significantly. The proportion of crops grown from seed treated with a non-mercurial fungicidal seed dressing reached a peak of 47% in 1986 but subsequently declined to 22% in 1990 and 1991.     

Inheritance and RAPD tagging of multiple genes for resistance to net blotch in barley.

A doubled haploid barley (Hordeum vulgare L.) population that was created from a cross between cultivars 'Léger' and 'CI 9831' was characterized by RAPD (random amplified polymorphic DNA) markers for resistance to isolate WRS857 of Pyrenophora teres Drechs. f. sp. maculata Smedeg., the causal agent of the spot form of net blotch. Resistance, which initially appeared to be conferred by a single gene from the approximate 1:1 (resistant : susceptible) segregation ratio of the doubled-haploid (DH) progeny, was found to be associated with three different genomic regions by RAPD analysis. Of 500 RAPD random primers that were screened against the parents, 195 revealed polymorphic bands, seven showed an association to the resistance in bulks, and these seven markers were mapped to three unlinked genomic regions. Two of these regions, one of which was mapped to chromosome 2, have major resistance genes. The third region has some homology to the chromosome 2 region. This study demonstrates the simultaneous location of markers for more than one gene governing a trait by using RAPD and bulked segregant analysis (BSA).     

Genome-wide association studies of net form of net blotch resistance at seedling and adult plant stages in spring barley collection

Net form of net blotch (NFNB) of barley (Hordeum vulgare L.), caused by Pyrenophora teres f. teres (Ptt) Drechsler (anamorph: Drechslera teres [Sacc.] Shoem.), is considered one of the major constraints of successful barley production in major barley growing regions of the world. Resistance to NFNB was evaluated in a barley collection of 336 genotypes (AM-2014), at seedling stage using isolates LGDPtt.19 and TD10 in the USA, and adult stage in seven hotspot environments in Morocco. The AM-2014 panel was genotyped with 9K SNP markers and genome-wide association studies (GWAS) were carried out using mixed linear model (MLM: Q?+?K) accounting for population structure (Q) and kinship (K) as covariates. Significant (P?<?0.001) marker trait associations were corrected for false discovery rate (FDR) at the q?<?0.05. Four genotypes showed an average infection response (IRs ≤ 2) to both isolates, LGDPttt.19 and TD10, at the seedling stage, and 30 genotypes showed resistance in all environments in the field while three genotypes exhibited the highest resistance at both stages. The GWAS of NFNB identified 31 distinct QTLs on all seven barley chromosomes, of which 8 with resistance at seedling stage, 21 were associated with resistance at the adult stage, and two QTLs, QRptt.2H-132.15 and QPtt.6H-54-55, conferred resistance at both stages. Of 31 resistance QTLs reported in this study, 10 QTLs coincided with previously mapped QTL while 21 are novel, thereby validating the GWAS approach used in this study. The resistance sources identified in AM-2014 and QTL mapped in this study are valuable resources for marker-assisted breeding for NFNB resistance in the future.     

Research advances in the Pyrenophora teres–barley interaction

Pyrenophora teres f. teres and P. teres f. maculata are significant pathogens that cause net blotch of barley. An increased number of loci involved in P. teres resistance or susceptibility responses of barley as well as interacting P. teres virulence effector loci have recently been identified through biparental and association mapping studies of both the pathogen and host. Characterization of the resistance/susceptibility loci in the host and the interacting effector loci in the pathogen will provide a path for targeted gene validation for better-informed release of resistant barley cultivars. This review assembles concise consensus maps for all loci published for both the host and pathogen, providing a useful resource for the community to be used in pathogen characterization and barley breeding for resistance to both forms of P. teres.