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Identification of Pyrenophora teres f. maculata , Causal Agent of Spot Type Net Blotch of Barley in North Dakota

Authors:
Zhaohui Liu at North Dakota State University
Zhaohui Liu
Timothy L Friesen at United States Department of Agriculture
Timothy L Friesen
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Abstract

Net blotch of barley (Hordeum vulgare L.) caused by the fungus Pyrenophora teres (anamorph Drechslera teres) is found in two forms, net form net blotch (NFNB) and spot form net blotch (SFNB). When inoculated on susceptible varieties, P. teres f. teres produces lesions with a characteristic net-like pattern surrounded by necrosis or chlorosis (NFNB), whereas P. teres f. maculata produces lesions consisting of spots surrounded by necrosis or chlorosis (SFNB). Recently, epidemics of SFNB have occurred throughout the world (4). Currently, net blotch is a significant foliar disease of barley in the North Dakota-Northwestern Minnesota agricultural region, a leading barley-production area. Diseased barley leaf tissue was collected annually from 2004 to 2008 in Fargo and Langdon, ND. Diseased leaves were incubated to promote sporulation. Ten single-spore isolates of P. teres collected from each location each year were tested for virulence by inoculation on 20 commonly used barley net blotch differential lines. Among the 100 isolates collected, one isolate collected in Fargo in 2006 (FGOH06Pt-8) and one isolate collected in Langdon in 2008 (LDNH08Pt-4) were identified as P. teres f. maculata due to their induction of spot-type lesions across the differential set. Conidial morphology of the two isolates was similar to P. teres f. teres isolates. A pathogenicity test of all isolates was performed on regional barley cvs. Tradition, Robust, and Lacey as well as barley lines Rika and Kombar (1) as previously described (3). The net form isolate 0-1 and spot form isolate DEN2.6 (obtained from B. Steffenson, University of Minnesota) were used as controls. The P. teres f. teres isolate 0-1 produced typical net type symptoms on all barley lines except the resistant line Rika, in which only small, dark spots were observed. DEN2.6 produced pin-point spot-like lesions with an extensive yellow halo on Robust, Lacey, Rika, and Kombar, but without chlorosis on Tradition. The two newly identified isolates induced elliptical spot-type lesions measuring 3 x 6 mm, larger than those produced by P. teres f. maculata isolate DEN 2.6, suggesting a higher level of virulence. We constructed a neighbor-joining phylogenetic tree using ClustalW2 (http://www.ebi.ac.uk/) based on sequence identity of the internal transcribed spacer (ITS) region from 0-1 (GenBank No. GU014819), DEN2.6 (GenBank No. GU014820), FGOH06Pt-8 (GenBank No. GU014821), and LDNH08Pt-4 (GenBank No. GU014822) as well as P. teres f. maculata, P. teres f. teres, and P. tritici-repentis (causal agent of tan spot of wheat) accessions obtained from GenBank (2). All P. teres isolates clustered together and were clearly separated from the P. tritici-repentis cluster. Isolates FGOH06Pt-8 and LDNH08Pt-4 had identical ITS sequences and differed from DEN2.6 by only a single nucleotide. To our knowledge, this is the first report of P. teres f. maculata in North Dakota. Resistance to SFNB should now be considered in local barley breeding programs and cultivar releases.
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April 2010, Volume 94, Number 4
Page 480
DOI: 10.1094/PDIS-94-4-0480A
Disease Notes
Identification of Pyrenophora teres f. maculata, Causal Agent of
Spot Type Net Blotch of Barley in North Dakota
Z. H. Liu, North Dakota State University, Fargo; and T. L. Friesen, USDA-ARS, Fargo, ND
Net blotch of barley (Hordeum vulgare L.) caused by the fungus Pyrenophora teres (anamorph Drechslera
teres) is found in two forms, net form net blotch (NFNB) and spot form net blotch (SFNB). When
inoculated on susceptible varieties, P. teres f. teres produces lesions with a characteristic net-like pattern
surrounded by necrosis or chlorosis (NFNB), whereas P. teres f. maculata produces lesions consisting of
spots surrounded by necrosis or chlorosis (SFNB). Recently, epidemics of SFNB have occurred throughout
the world (4). Currently, net blotch is a significant foliar disease of barley in the North Dakota-
Northwestern Minnesota agricultural region, a leading barley-production area. Diseased barley leaf tissue
was collected annually from 2004 to 2008 in Fargo and Langdon, ND. Diseased leaves were incubated to
promote sporulation. Ten single-spore isolates of P. teres collected from each location each year were
tested for virulence by inoculation on 20 commonly used barley net blotch differential lines. Among the
100 isolates collected, one isolate collected in Fargo in 2006 (FGOH06Pt-8) and one isolate collected in
Langdon in 2008 (LDNH08Pt-4) were identified as P. teres f. maculata due to their induction of spot-type
lesions across the differential set. Conidial morphology of the two isolates was similar to P. teres f. teres
isolates. A pathogenicity test of all isolates was performed on regional barley cvs. Tradition, Robust, and
Lacey as well as barley lines Rika and Kombar (1) as previously described (3). The net form isolate 0-1
and spot form isolate DEN2.6 (obtained from B. Steffenson, University of Minnesota) were used as
controls. The P. teres f. teres isolate 0-1 produced typical net type symptoms on all barley lines except the
resistant line Rika, in which only small, dark spots were observed. DEN2.6 produced pin-point spot-like
lesions with an extensive yellow halo on Robust, Lacey, Rika, and Kombar, but without chlorosis on
Tradition. The two newly identified isolates induced elliptical spot-type lesions measuring 3 × 6 mm, larger
than those produced by P. teres f. maculata isolate DEN 2.6, suggesting a higher level of virulence. We
constructed a neighbor-joining phylogenetic tree using ClustalW2 (http://www.ebi.ac.uk/) based on
sequence identity of the internal transcribed spacer (ITS) region from 0-1 (GenBank No. GU014819),
DEN2.6 (GenBank No. GU014820), FGOH06Pt-8 (GenBank No. GU014821), and LDNH08Pt-4 (GenBank
No. GU014822) as well as P. teres f. maculata, P. teres f. teres, and P. tritici-repentis (causal agent of tan
spot of wheat) accessions obtained from GenBank (2). All P. teres isolates clustered together and were
clearly separated from the P. tritici-repentis cluster. Isolates FGOH06Pt-8 and LDNH08Pt-4 had identical
ITS sequences and differed from DEN2.6 by only a single nucleotide. To our knowledge, this is the first
report of P. teres f. maculata in North Dakota. Resistance to SFNB should now be considered in local
barley breeding programs and cultivar releases.
Reference: (1) M. Abu Qamar. Theor. Appl. Genet. 117:1261, 2008. (2) R. M. Andrie et al. Fungal Genet.
Biol. 45:363, 2008. (3) Z. Lai et al. Fungal Genet. Biol. 44:323, 2007. (4) M. S. McLean et al. Crop
Pasture Sci. 60:303, 2009.
... Ptt and Ptm diverged well before the onset of plant domestication and agriculture, likely in different regions and/ or on different hosts, with relatively recent secondary contact on barley [42,43]. Although Ptt and Ptm both have global distributions, their relative abundance changes over time and space, with one form generally predominant in a given region [44][45][46]. The genetic structure of Ptm has been elucidated regionally, but its global structure remains unknown [37,[47][48][49]. ...
... Ptt was present in all of the sampled areas in France, whereas Ptm was only found in the southwest of the country, where it coexisted with Ptt in the same field. This pattern is similar to what has been reported in other regions of Eastern and Northern Europe, North America, Italy, the Maghreb, and Egypt, where the two forms are present, but Ptt clearly predominates [37,46,64,80,[83][84][85][86][87][88][89][90][91][92]. Our results, however, contrast with what was observed in East Africa, South Africa, and Southeastern Australia, where Ptm is more prevalent [44,82,93]. ...
Deep population structure linked to host vernalization requirement in the barley net blotch fungal pathogen
Article
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  • May 2024
Invasive fungal pathogens pose a substantial threat to widely cultivated crop species, owing to their capacity to adapt to new hosts and new environmental conditions. Gaining insights into the demographic history of these pathogens and unravelling the mechanisms driving coevolutionary processes are crucial for developing durably effective disease management programmes. Pyrenophora teres is a significant fungal pathogen of barley, consisting of two lineages, Ptt and Ptm, with global distributions and demographic histories reflecting barley domestication and spread. However, the factors influencing the population structure of P. teres remain poorly understood, despite the varietal and environmental heterogeneity of barley agrosystems. Here, we report on the population genomic structure of P. teres in France and globally. We used genotyping-by-sequencing to show that Ptt and Ptm can coexist in the same area in France, with Ptt predominating. Furthermore, we showed that differences in the vernalization requirement of barley varieties were associated with population differentiation within Ptt in France and at a global scale, with one population cluster found on spring barley and another population cluster found on winter barley. Our results demonstrate how cultivation conditions, possibly associated with genetic differences between host populations, can be associated with the maintenance of divergent invasive pathogen populations coexisting over large geographic areas. This study not only advances our understanding of the coevolutionary dynamics of the Pt-barley pathosystem but also prompts further research on the relative contributions of adaptation to the host versus adaptation to abiotic conditions in shaping Ptt populations.
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... This filamentous fungal pathogen is endemic worldwide and can be found in two different forms, Pyrenophora teres f. teres and Pyrenophora teres f. maculata. Although both forms of P. teres are present in all major barley growing regions, it is common for one form to be locally dominant, with the predominant form often changing over time (Liu and Friesen 2010;Louw et al. 1996;McLean et al. 2009). Though morphologically similar, the two forms are distinguished based on the physiology of disease symptoms observed on the surface of barley leaves. ...
... P. teres f. maculata has recently increased in prominence in the USA and Australia, causing yield losses of up to 44% (Liu and Friesen 2010;Marshall et al. 2015;McClean et al. 2010;Jayasena et al. 2007). In Australia, potential losses caused by this pathogen have been valued at AU$192 million per year (Murray and Brennan 2010). ...
Host and pathogen genetics reveal an inverse gene-for-gene association in the P. teres f. maculata–barley pathosystem
Article
Full-text available
  • Sep 2022
  • THEOR APPL GENET
Key message Pathogen and host genetics were used to uncover an inverse gene-for-gene interaction where virulence genes from the pathogen Pyrenophora teres f. maculata target barley susceptibility genes, resulting in disease. Abstract Although models have been proposed to broadly explain how plants and pathogens interact and coevolve, each interaction evolves independently, resulting in various scenarios of host manipulation and plant defense. Spot form net blotch is a foliar disease of barley caused by Pyrenophora teres f. maculata. We developed a barley population (Hockett × PI 67381) segregating for resistance to a diverse set of P. teres f. maculata isolates. Quantitative trait locus analysis identified major loci on barley chromosomes (Chr) 2H and 7H associated with resistance/susceptibility. Subsequently, we used avirulent and virulent P. teres f. maculata isolates to develop a pathogen population, identifying two major virulence loci located on Chr1 and Chr2. To further characterize this host–pathogen interaction, progeny from the pathogen population harboring virulence alleles at either the Chr1 or Chr2 locus was phenotyped on the Hockett × PI 67381 population. Progeny harboring only the Chr1 virulence allele lost the barley Chr7H association but maintained the 2H association. Conversely, isolates harboring only the Chr2 virulence allele lost the barley Chr2H association but maintained the 7H association. Hockett × PI 67381 F2 individuals showed susceptible/resistant ratios not significantly different than 15:1 and results from F2 inoculations using the single virulence genotypes were not significantly different from a 3:1 (S:R) ratio, indicating two dominant susceptibility genes. Collectively, this work shows that P. teres f. maculata virulence alleles at the Chr1 and Chr2 loci are targeting the barley 2H and 7H susceptibility alleles in an inverse gene-for-gene manner to facilitate colonization.
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... In addition, one form of net blotch is often dominant within a barley-growing region [2,39,40]. In fact, for example, P. teres f. maculata has become more prevalent in North Dakota (USA), Idaho (USA), Victoria (Australia), Turkey, and the western provinces of Algeria [41][42][43][44][45]. Conversely, P. teres f. teres is the most Considering both experimental years and the two malting barley cultivars (Quench and Sunshine) together, we found that P. teres f. teres accumulation in grains showed a positive and significant correlation (r = 0.70; p = 0.000001) with NFNB symptoms observed at BBCH 80 (30 days after fungicide application). ...
... In addition, one form of net blotch is often dominant within a barley-growing region [2,39,40]. In fact, for example, P. teres f. maculata has become more prevalent in North Dakota (USA), Idaho (USA), Victoria (Australia), Turkey, and the western provinces of Algeria [41][42][43][44][45]. Conversely, P. teres f. teres is the most present form in northeastern Algeria, East Azerbaijan, Finland, and in most parts of the Ethiopian highlands [46][47][48][49]. ...
Management of Pyrenophora teres f. teres, the Causal Agent of Net Form Net Blotch of Barley, in A Two-Year Field Experiment in Central Italy
Article
Full-text available
  • Feb 2022
Pyrenophora teres is the causal agent of barley net blotch (NB), a disease that can be found in two different forms: net form (NFNB), caused by P. teres f. teres, and spot form (SFNB), caused by P. teres f. maculata. A two-year field experiment was carried out to evaluate the response to NB of six different barley cultivars for malt or feed/food production. In addition, the efficacy of several recently developed foliar fungicides with different modes of action (SDHI, DMI, and QoI) towards the disease was examined. After NB leaf symptom evaluation, the identification of P. teres forms was performed. Grain yield was determined, and pathogen biomass was quantified in the grain by qPCR. In the two experimental years characterized by different climatic conditions, only P. teres f. teres was detected. The tested cultivars showed different levels of NFNB susceptibility. In particular, the two-row cultivars for malt production showed the highest disease incidence. All applied fungicides exhibited a high efficacy in reducing disease symptoms on leaves and pathogen accumulation in grains. In fact, high levels of fungal biomass were detected only in the grain of the untreated malting barley cultivars. For some cultivars, grain yield was positively influenced by the application of fungicides.
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Juvenile Resistance of Barley Cultivars and Accessions to Net-, Spot-, and Hybrid (Net × Spot) Forms of Pyrenophora teres
Article
  • Jan 2023
Barley net blotch is an economically important disease. The causative agent is an ascomycete, Pyrenophora teres, which exists in two forms: P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), which differ in their symptoms on barley plants. These two forms are easily crossed in laboratory conditions with the formation of fertile offspring, however, it is extremely difficult to prove the hybrid nature of fungal isolates, sometimes found in natural populations of the pathogen and bearing signs of both forms. In 2020, we first identified Ptt × Ptm hybrids in natural populations of P. teres in Krasnodar Region in isolates collected in 2016. The aim of the studies was to compare the virulence of two Ptt isolates, two Ptm isolates of different origin and a hybrid isolate Ptt × Ptm to a wide set of barley genotypes from the VIR collection pre-selected for Ptt resistance, to determine variability of the virulence trait in the hybrid isolate and characterize resistance to both forms of the fungus and hybrid. Depending on the barley genotype, 3 types of disease symptoms were manifested upon inoculation with the Ptt × Ptm hybrid isolate: (1) similar to Ptt, (2) similar to Ptm, and (3) a mixed type. Apparently, the manifestation of symptoms after inoculation with the hybrid isolate depends on the barley genotype influencing the expression of certain pathogen effector genes. It was shown that in most cases Ptm isolates differ in virulence from Ptt isolates to the same barley genotypes, and the Ptt × Ptm hybrid isolate from both Ptt and Ptm. On average, the Ptt × Ptm hybrid isolate was less aggressive than the Ptt and Ptm isolates. A comparison of the types of responses of barley genotypes to all studied isolates of Ptt and Ptm revealed 8.8% of genotypes resistant to both forms of P. teres and 5.6% to Ptt, Ptm and the hybrid isolate Ptt × Ptm. The virulence of natural hybrid between two forms of P. teres Ptt × Ptm was studied for the first time. The barley genotypes resistant to the two forms of the net blotch are valuable source of resistance for barley breeding.
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Deep population structure linked to host vernalization requirement in the barley net blotch fungal pathogen
Preprint
Full-text available
  • Dec 2023
Invasive fungal pathogens pose a substantial threat to widely cultivated crop species, owing to their capacity to adapt to new hosts and new environmental conditions. Gaining insights into the demographic history of these pathogens and unraveling the mechanisms driving coevolutionary processes are crucial for the development of durably effective disease management programs. Pyrenophora teres is a significant fungal pathogen of barley, consisting of two lineages, Ptt and Ptm, with global distributions and demographic histories reflecting barley domestication and spread. However, the factors influencing the population structure of P. teres remain poorly understood, despite the varietal and environmental heterogeneity of barley agrosystems. Here, we report on the population genomic structure of P. teres in France and globally. We used genotyping-by-sequencing to show that Ptt and Ptm can coexist in the same area in France, with Ptt predominating. Furthermore, we showed that differences in the vernalization requirement of barley varieties were associated with population differentiation in France and at a global scale, with one population cluster found on spring barley and another population cluster found on winter barley. Our results demonstrate how cultivation conditions, possibly associated with genetic differences between host populations, can be associated with the maintenance of divergent invasive pathogen populations coexisting over large geographic areas. This study not only advances our understanding of the coevolutionary dynamics of the Pt-barley pathosystem but also prompts further research on the relative contributions of adaptation to the host versus adaptation to abiotic conditions in shaping Ptt populations. Impact statement Many invasive fungal pathogens have successfully followed major crop species throughout their intercontinental range, but continue to represent dynamic biotic threats. During their geographic expansion, invasive fungal populations were subjected to heterogeneous environmental conditions, or different populations of hosts, which could result in adaptation processes. Understanding this history of colonization can allow us to better prevent the emergence of infectious diseases of crops, and to better control them. One such fungus, Pyrenophora teres , negatively impacts barley production globally by causing net blotch disease. In this study, we characterized the genetic makeup of P. teres in France and how it compares with what can be sampled in other regions of the world. We found that both the net and spot forms of Pyrenophora teres can be in the same area in France, but the spot form is more common. We also discovered that the net form populations associated with winter and spring barley are different, which was not known until now. This study opens up numerous experimental perspectives aimed at evaluating whether the two populations of net form are adapted to their hosts or to the conditions of cultivation of their hosts, with the goal of implementing measures that force the pathogen to maladaptation. Data summary GBS data are available under BioProject PRJEB66440. Single nucleotide polymorphism and reference genome assembly are available under doi: https://doi.org/10.5281/zenodo.10021844 . Reads used for genome assembly are available under the BioProject PRJEB66476. The authors confirm all supporting data, code, and protocols have been provided within the article or through supplementary data files.
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SDHI resistance in Pyrenophora teres f teres and molecular detection of novel double mutations in sdh genes conferring high resistance
Article
Full-text available
BACKGROUND Net blotch (NB), caused by Pyrenophora teres f. teres (Ptt), is an important disease of barley worldwide. NB control is commonly achieved through the use of fungicide mixtures including strobilurins, triazoles and carboxamides. Succinate dehydrogenase inhibitors (SDHI) are important components of fungicide management programs of barley diseases. However, during the last growing seasons in Argentina, barley fields sprayed with mixtures containing SDHI fungicides have shown failures in NB control. Here, we report the isolation and characterization of Argentine Ptt strains resistant to SDHI fungicides. RESULTS Compared against a sensitive (wild‐type) reference strain collected in 2008, all 21 Ptt isolates collected in 2021 exhibited resistance to pydiflumetofen and fluxapyroxad both in vitro and in vivo. Concordantly, all of them presented target‐site mutations in any of the sdhB, sdhC and sdhD genes. Although the mutations detected have been previously reported in other parts of the world, this study documents for the first time the occurrence of double mutations in the same Ptt isolate. Specifically, the double mutation sdhC‐N75S + sdhD‐D145G confers high resistance to SDHI fungicides, while the double mutations sdhB‐H277Y + sdhC‐N75S and sdhB‐H277Y + sdhC‐H134R confer moderate levels of resistance in Ptt. CONCLUSIONS SDHI‐resistance in Argentine Ptt populations is expected to increase. These findings emphasize the urgent need to perform a wider survey and a more frequent monitoring of SDHI sensitivity of Ptt populations and to develop and implement effective antiresistance tactics. © 2023 Society of Chemical Industry.
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Recommended rates of azoxystrobin and tebuconazole seem to be environmentally safe but ineffective against target fungi
Article
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  • Jan 2023
  • ECOTOXICOLOGY
The use of fungicides in agriculture has been playing a role in the enhancement of agricultural yields through the control of pathogens causing serious diseases in crops. Still, adverse environmental and human health effects resulting from its application have been reported. In this study, the possibility of readjusting the formulation of a commercial product combining azoxystrobin and tebuconazole (active ingredients – AIs; Custodia®) towards environmentally safer alternative(s) was investigated. Specifically, the sensitivity of non-target aquatic communities to each AI was first evaluated by applying the Species Sensitivity Distributions (SSDs) approach. Then, mixtures of these AIs were tested in a non-target organism ( Raphidocelis subcapitata ) denoting sensitivity to both AIs as assessed from SSDs. The resulting data supported the design of the last stage of this study, where mixtures of those AIs at equivalent vs . alternative ratios and rates as in the commercial formulation were tested against two target fungal species: Pyrenophora teres CBS 123929 and Rhynchosporium secalis CBS 110524. The comparison between the sensitivity of non-target aquatic species and the corresponding efficacy towards target fungi revealed that currently applied mixture and rates of these AIs are generally environmentally safe (antagonistic interaction; concentrations below the EC 1 for R. subcapitata and generally below the HC 5 for aquatic non-target communities), but ineffective against target organisms (maximum levels of inhibition of 70 and 50% in P. teres CBS 123929 and R. secalis CBS 110524, respectively). Results additionally suggest a potentiation of the effects of the AIs by the other formulants added to the commercial product at tested rates. Overall, this study corroborates that commercial products can be optimized during design stages based on a systematic ecotoxicological testing for ingredient interactions and actual efficacy against targets. This could be a valuable pathway to reduce environmental contamination during transition to a more sustainable agricultural production.
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CHARACTERIZATION OF Cochliobolus sativus AND Pyrenophora teres FUNGI BELONGING TO THE LEAF SPOT COMPLEX OF BARLEY (Hordeum vulgare) ISOLATED FROM BARLEY SEEDS IN MEXICO
Article
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  • Mar 2021
Barley (Hordeum vulgare) is generally used for animal feed, and food and beer production industries. Its production is affected by phytopathogens, of which Ramularia collo-cygni, Puccinia spp., Pyrenophora teres and Cochliobolus sativus are of global concern. In Mexico, there are few studies available on the morphological and molecular identification of fungi responsible for causing fungal diseases of barley. Therefore, the objective of this work was to identify, morphologically and molecularly, fungi isolated from barley seeds. The strains were identified by morphological analysis and by sequencing of the conserved ITS1/5.8s/ITS2 region of the ribosomal gene. Morphologically, the strains were identified as P. teres and C. sativus, which was confirmed with bioinformatics techniques using BLAST and MEGA6 programs. The results showed that the strains isolated from barley seeds in the highlands of Mexico were consistent with the sequences of P. teres and C. sativus deposited in the GenBank. These results will allow identifying some of the species of native fungi found in barley seeds.
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Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: A review
Article
Full-text available
  • Jan 2009
Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.
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A region of barley chromosome 6H harbors multiple major genes associated with net type net blotch resistance
Article
Full-text available
  • Sep 2008
Net type net blotch (NTNB), caused by Pyrenophora teres f. teres Drechs., is prevalent in barley growing regions worldwide. A population of 118 doubled haploid (DH) lines developed from a cross between barley cultivars 'Rika' and 'Kombar' were used to evaluate resistance to NTNB due to their differential reaction to various isolates of P. teres f. teres. Rika was resistant to P. teres f. teres isolate 15A and susceptible to isolate 6A. Conversely, Kombar was resistant to 6A, but susceptible to 15A. A progeny isolate of a 15A x 6A cross identified as 15A x 6A#4 was virulent on both parental lines. The Rika/Kombar (RK) DH population was evaluated for disease reactions to the three isolates. Isolate 15A induced a resistant:susceptible ratio of 78:40 (R:S) whereas isolate 6A induced a resistant:susceptible ratio of 40:78. All but two lines had opposite disease reactions indicating two major resistance genes linked in repulsion. Progeny isolate 15A x 6A#4 showed a resistant:susceptible ratio of 1:117 with the one resistant line also being the single line that was resistant to both 15A and 6A. An RK F(2) population segregated in a 1:3 (R:S) ratio for both 15A and 6A indicating that resistance is recessive. Molecular markers were used to identify a region on chromosome 6H that harbors the two NTNB resistance genes. This work shows that multiple NTNB resistance genes exist at the locus on chromosome 6H, and the recombinant DH line harboring the resistance alleles from both parents will be useful for the development of NTNB-resistant barley germplasm.
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Genetic mapping of Pyrenophora teres f. teres genes conferring avirulence on barley
Article
  • Jun 2007
A Pyrenophora teres f. teres cross between isolates 0-1 and 15A was used to evaluate the genetics of avirulence associated with barley lines Canadian Lake Shore (CLS), Tifang, and Prato. 15A is avirulent on Tifang and CLS, but virulent on Prato. Conversely, 0-1 is avirulent on Prato, but virulent on Tifang and CLS. Avirulence:virulence on Tifang and CLS segregated 1:1, whereas avirulence:virulence on Prato segregated 3:1. An AFLP-based linkage map was constructed and used to identify a single locus derived from 15A (AvrHar) conferring avirulence to Tifang and CLS. Virulence on Prato was conferred by two epistatic genes (AvrPra1 and AvrPra2). AvrPra2 co-segregated with AvrHar, but the two genes from opposite parents conferred opposite reactions. This work provides the foundation for the isolation of these avirulence genes.
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Homologs of ToxB, a host-selective toxin gene from Pyrenophora tritici-repentis, are present in the genome of sister-species Pyrenophora bromi and other members of the Ascomycota
Article
  • Apr 2008
  • FUNGAL GENET BIOL
Pyrenophora tritici-repentis requires the production of host-selective toxins (HSTs) to cause the disease tan spot of wheat, including Ptr ToxA, Ptr ToxB, and Ptr ToxC. Pyrenophora bromi, the species most closely related to P. tritici-repentis, is the causal agent of brown leaf spot of bromegrass. Because of the relatedness of P. bromi and P. tritici-repentis, we investigated the possibility that P. bromi contains sequences homologous to ToxA and/or ToxB, the products of which may be involved in its interaction with bromegrass. Multiplex polymerase chain reaction (PCR) revealed the presence of ToxB-like sequences in P. bromi and high-fidelity PCR was used to clone several of these loci, which were subsequently confirmed to be homologous to ToxB. Additionally, Southern analysis revealed ToxB from P. bromi to have a multicopy nature similar to ToxB from P. tritici-repentis. A combination of phylogenetic and Southern analyses revealed that the distribution of ToxB extends further into the Pleosporaceae, and a search of available fungal genomes identified a distant putative homolog in Magnaporthe grisea, causal agent of rice blast. Thus, unlike most described HSTs, ToxB homologs are present across a broad range of plant pathogenic ascomycetes, suggesting that it may have arose in an early ancestor of the Ascomycota.
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  • Jan 2008
  • THEOR APPL GENET
  • 1261
  • Abu Qamar
Reference: (1) M. Abu Qamar. Theor. Appl. Genet. 117:1261, 2008. (2) R. M. Andrie et al. Fungal Genet.
  • Jan 2007
  • FUNGAL GENET BIOL
  • 303
  • Z Lai
Biol. 45:363, 2008. (3) Z. Lai et al. Fungal Genet. Biol. 44:323, 2007. (4) M. S. McLean et al. Crop Pasture Sci. 60:303, 2009.