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Sexual and asexual dispersal structures of Pyrenophora teres f. teres. (a) Conidia (grey arrow), conidiophores (black arrow) and mycelium (white arrow). Scale bar, 40 mm. (b) Conidia containing three to five septa. Scale bar, 40 mm. (c) Barley straw containing dark fungal pseudothecia. Scale bar, 2.5 mm. (d) Immature pseudothecia showing the globose shape and the dark-brown, hair-like setae. Scale bar, 1 mm. (e) The breakage of a pseudothecia showing immature, bitunicate asci (black arrow), and a mature asci (white arrow) in which the inner wall has erupted and a few ascospores have been ejected. Scale bar, 80 mm. (f) Close look at the ascospores that have three or four transverse septa and one or two longitudinal septa in the median cells. Scale bar, 20 mm.
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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 for...
Contexts in source publication
Context 1
... forms of net blotch are classified as stubble-borne diseases because the fungus usually produces the ascocarp (pseudoth- ecia) as an over-seasoning structure on infected barley debris left (on the surface) after harvest (Figs 2 and 3). As a result of their similarities, the life cycle of the two forms are addressed jointly. The pseudothecia are spherical structures seen as many dark dots on the surface of barley straw (Fig. 2). Pseudothecia are 1-2 mm in diameter and are covered by dark, hair-like setae (Mathre, 1997;McLean et al., 2009; Fig. 2). The pseudothecia of P. teres have been observed in both field and laboratory envi- ronments, but, because of the heterothallic nature of P. teres, successful development of the sexual fruiting body requires strains with opposite mating types ( Rau et al., 2005), as well as specific environmental conditions (Kenneth, 1962;McDonald, 1963). Club-shaped and bitunicate asci, measuring 30-61 mm ¥ 180-274 mm, develop within the mature and fertile pseudoth- ecia ( Fig. 2) (Mathre, 1997;Webster, 1951). Each ascus generally contains eight ascospores that are 18-28 mm ¥ 43-61 mm in size, light-brown and often have three or four transverse septa and one or two longitudinal septa only in the median cells (Mathre, 1997;Webster, 1951) (Fig. 2). Mature ascospores are actively discharged, dispersed by wind and serve as primary inoculum early in the growing season (Jordan, 1981) (Fig. 3). In some cases, seed-borne mycelium and conidia released from the stubble of barley or an alternative host can also serve as primary inoculum for early season infection (Jordan and Allen, 1984;Louw et al., 1996;McLean et al., 2009;Shipton et al., ...
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... forms of net blotch are classified as stubble-borne diseases because the fungus usually produces the ascocarp (pseudoth- ecia) as an over-seasoning structure on infected barley debris left (on the surface) after harvest (Figs 2 and 3). As a result of their similarities, the life cycle of the two forms are addressed jointly. The pseudothecia are spherical structures seen as many dark dots on the surface of barley straw (Fig. 2). Pseudothecia are 1-2 mm in diameter and are covered by dark, hair-like setae (Mathre, 1997;McLean et al., 2009; Fig. 2). The pseudothecia of P. teres have been observed in both field and laboratory envi- ronments, but, because of the heterothallic nature of P. teres, successful development of the sexual fruiting body requires strains with opposite mating types ( Rau et al., 2005), as well as specific environmental conditions (Kenneth, 1962;McDonald, 1963). Club-shaped and bitunicate asci, measuring 30-61 mm ¥ 180-274 mm, develop within the mature and fertile pseudoth- ecia ( Fig. 2) (Mathre, 1997;Webster, 1951). Each ascus generally contains eight ascospores that are 18-28 mm ¥ 43-61 mm in size, light-brown and often have three or four transverse septa and one or two longitudinal septa only in the median cells (Mathre, 1997;Webster, 1951) (Fig. 2). Mature ascospores are actively discharged, dispersed by wind and serve as primary inoculum early in the growing season (Jordan, 1981) (Fig. 3). In some cases, seed-borne mycelium and conidia released from the stubble of barley or an alternative host can also serve as primary inoculum for early season infection (Jordan and Allen, 1984;Louw et al., 1996;McLean et al., 2009;Shipton et al., ...
Context 3
... forms of net blotch are classified as stubble-borne diseases because the fungus usually produces the ascocarp (pseudoth- ecia) as an over-seasoning structure on infected barley debris left (on the surface) after harvest (Figs 2 and 3). As a result of their similarities, the life cycle of the two forms are addressed jointly. The pseudothecia are spherical structures seen as many dark dots on the surface of barley straw (Fig. 2). Pseudothecia are 1-2 mm in diameter and are covered by dark, hair-like setae (Mathre, 1997;McLean et al., 2009; Fig. 2). The pseudothecia of P. teres have been observed in both field and laboratory envi- ronments, but, because of the heterothallic nature of P. teres, successful development of the sexual fruiting body requires strains with opposite mating types ( Rau et al., 2005), as well as specific environmental conditions (Kenneth, 1962;McDonald, 1963). Club-shaped and bitunicate asci, measuring 30-61 mm ¥ 180-274 mm, develop within the mature and fertile pseudoth- ecia ( Fig. 2) (Mathre, 1997;Webster, 1951). Each ascus generally contains eight ascospores that are 18-28 mm ¥ 43-61 mm in size, light-brown and often have three or four transverse septa and one or two longitudinal septa only in the median cells (Mathre, 1997;Webster, 1951) (Fig. 2). Mature ascospores are actively discharged, dispersed by wind and serve as primary inoculum early in the growing season (Jordan, 1981) (Fig. 3). In some cases, seed-borne mycelium and conidia released from the stubble of barley or an alternative host can also serve as primary inoculum for early season infection (Jordan and Allen, 1984;Louw et al., 1996;McLean et al., 2009;Shipton et al., ...
Context 4
... forms of net blotch are classified as stubble-borne diseases because the fungus usually produces the ascocarp (pseudoth- ecia) as an over-seasoning structure on infected barley debris left (on the surface) after harvest (Figs 2 and 3). As a result of their similarities, the life cycle of the two forms are addressed jointly. The pseudothecia are spherical structures seen as many dark dots on the surface of barley straw (Fig. 2). Pseudothecia are 1-2 mm in diameter and are covered by dark, hair-like setae (Mathre, 1997;McLean et al., 2009; Fig. 2). The pseudothecia of P. teres have been observed in both field and laboratory envi- ronments, but, because of the heterothallic nature of P. teres, successful development of the sexual fruiting body requires strains with opposite mating types ( Rau et al., 2005), as well as specific environmental conditions (Kenneth, 1962;McDonald, 1963). Club-shaped and bitunicate asci, measuring 30-61 mm ¥ 180-274 mm, develop within the mature and fertile pseudoth- ecia ( Fig. 2) (Mathre, 1997;Webster, 1951). Each ascus generally contains eight ascospores that are 18-28 mm ¥ 43-61 mm in size, light-brown and often have three or four transverse septa and one or two longitudinal septa only in the median cells (Mathre, 1997;Webster, 1951) (Fig. 2). Mature ascospores are actively discharged, dispersed by wind and serve as primary inoculum early in the growing season (Jordan, 1981) (Fig. 3). In some cases, seed-borne mycelium and conidia released from the stubble of barley or an alternative host can also serve as primary inoculum for early season infection (Jordan and Allen, 1984;Louw et al., 1996;McLean et al., 2009;Shipton et al., ...
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... initial colonization, the fungus produces a large number of conidia which serve as secondary inocula (Figs 2 and 3). Conidia are borne on top of conidiophores that are slightly swollen at the base and usually arise singly or in groups of two or three. Conidia measuring 30-174 mm ¥ 15-23 mm are smooth, cylindrical and straight, round at both ends, subhyaline to yellow- ish brown, and often with four to six pseudosepta ( Fig. 2) (Mathre, 1997;McLean et al., 2009;Webster, 1951). Conidia are produced throughout the growing season and are dispersed by strong wind or rain to cause new infections on plants locally, or can be carried longer distances potentially to new barley fields (Jordan, 1981;Mathre, 1997) (Fig. 3).The dispersion, germination and successful infection of conidia are greatly influenced by the relative humid- ity, temperature, leaf wetness and other environmental factors (van den Berg andRossnagel, 1990, 1991;Jordan, 1981). During the growing season, several secondary cycles can occur, causing high disease severity on susceptible plants if environmental con- ditions are favourable (Fig. 3). At the end of the growing season, the fungus colonizes the senescent tissue, ultimately producing pseudothecia, the protective teleomorph structure used for over- seasoning (Figs 2 and ...
Context 6
... initial colonization, the fungus produces a large number of conidia which serve as secondary inocula (Figs 2 and 3). Conidia are borne on top of conidiophores that are slightly swollen at the base and usually arise singly or in groups of two or three. Conidia measuring 30-174 mm ¥ 15-23 mm are smooth, cylindrical and straight, round at both ends, subhyaline to yellow- ish brown, and often with four to six pseudosepta ( Fig. 2) (Mathre, 1997;McLean et al., 2009;Webster, 1951). Conidia are produced throughout the growing season and are dispersed by strong wind or rain to cause new infections on plants locally, or can be carried longer distances potentially to new barley fields (Jordan, 1981;Mathre, 1997) (Fig. 3).The dispersion, germination and successful infection of conidia are greatly influenced by the relative humid- ity, temperature, leaf wetness and other environmental factors (van den Berg andRossnagel, 1990, 1991;Jordan, 1981). During the growing season, several secondary cycles can occur, causing high disease severity on susceptible plants if environmental con- ditions are favourable (Fig. 3). At the end of the growing season, the fungus colonizes the senescent tissue, ultimately producing pseudothecia, the protective teleomorph structure used for over- seasoning (Figs 2 and ...
Context 7
... initial colonization, the fungus produces a large number of conidia which serve as secondary inocula (Figs 2 and 3). Conidia are borne on top of conidiophores that are slightly swollen at the base and usually arise singly or in groups of two or three. Conidia measuring 30-174 mm ¥ 15-23 mm are smooth, cylindrical and straight, round at both ends, subhyaline to yellow- ish brown, and often with four to six pseudosepta ( Fig. 2) (Mathre, 1997;McLean et al., 2009;Webster, 1951). Conidia are produced throughout the growing season and are dispersed by strong wind or rain to cause new infections on plants locally, or can be carried longer distances potentially to new barley fields (Jordan, 1981;Mathre, 1997) (Fig. 3).The dispersion, germination and successful infection of conidia are greatly influenced by the relative humid- ity, temperature, leaf wetness and other environmental factors (van den Berg andRossnagel, 1990, 1991;Jordan, 1981). During the growing season, several secondary cycles can occur, causing high disease severity on susceptible plants if environmental con- ditions are favourable (Fig. 3). At the end of the growing season, the fungus colonizes the senescent tissue, ultimately producing pseudothecia, the protective teleomorph structure used for over- seasoning (Figs 2 and ...
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Citations
... Pyrenophora teres is a major fungal pathogen of barley, present in all areas of barley cultivation [30][31][32][33]. Pyrenophora teres exists as two distinct lineages (called forms) that cause different symptoms. ...
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.
... Ptm is closely related, but genetically distinct from, P. teres f. teres (Ptt, Ellwood et al. 2012;Syme et al. 2018), the cause of net form net blotch (NFNB), producing ovoid rather than net-like striated disease symptoms. Ptm is classed as a hemi-biotroph, with a short asymptomatic or biotrophic phase followed by necrotrophy (Liu et al. 2011). Although hybridisation may occur between the two pathogens, this is uncommon (Poudel et al. 2017;Poudel et al. 2019) with hybrids showing lower fitness in planta, reduced recombination rates and negative epistasis between parental alleles at several loci (Yuzon et al. 2023). ...
... The first definitive report of SFNB was by Smedegård-Petersen (1971) in Denmark and the disease has since emerged as notable disease on commercial barley across all major growing regions (reviewed in McLean et al. 2009). The pathogen persists in stubble as pseudothecia containing ascospores, with both ascospores and later asexual conidia from diseased plants dispersed by air turbulence and water splash (Liu et al. 2011). This dual mode of propagation allows both recombination and clonal expansion, rapidly disseminating new alleles, gene combinations or fungicide resistance mutations that provide an adaptive advantage (Mair et al. 2020;Muria-Gonzalez et al. 2023). ...
... Notable exceptions to the conventional gene-for-gene model are the recessive mlo and rbgh2 genes that prime host defences against powdery mildews (Ge et al. 2020;Ge et al. 2016;Moolhuijzen et al. 2023). Both models occur in net blotch-barley interactions (Liu et al. 2011;Muria-Gonzalez et al. 2023;Williams et al. 1999), with early host detection of the pathogen at the asymptomatic or biotrophic phase likely determining gene-for-gene resistance, followed by the inverse model in the necrotrophic phase. ...
Spot form of net blotch, caused by Pyrenophora teres f. maculata, is a significant necrotrophic disease of barley that spread world-wide in the 20th century. Genetic relationships were analysed to determine the diversity, survival and dispersal of a diverse collection of 346 isolates from Australia, Southern Africa, North America, Asia Minor and Europe. The results, based on genome-wide DArTseq data, indicated isolates from Turkey were the most differentiated with regional sub-structuring, together with individuals closely related to geographically distant genotypes. Elsewhere, population subdivision related to country of origin was evident, although low levels of admixturing was found that may represent rare genotypes or migration from unsampled populations. Canadian isolates were the next most diverged and Australian and South African the most closely related. With the exception of Turkish isolates, multiple independent Cyp51A mutation events (which confer insensitivity to demethylation inhibitor fungicides) between countries and within regions was evident, with strong selection for a transposable element insertion at the 3’ end of the promoter and counter-selection elsewhere. Individuals from Western Australia shared genomic regions and Cyp51A haplotypes with South African isolates, suggesting a recent common origin.
... Ptt is a seedborne pathogen, and gene flow or introduction of isolates with new traits (for example, target site mutations in fungicide target proteins) is possible through seed trade, then evolving and adapting to local environments, and through selection pressure of host cultivars and fungicide applications [12]. Farmers in Estonia import new batches of barley seed of various cultivars from Finnish, Danish, German, and other breeding companies, in addition to propagating seeds themselves. ...
... Ptt has a mixed reproduction system, which contributes to the evolution of the pathogen [12]. Equal distribution of the two mating types is assumed in the absence of segregation bias and selection of one mating type [9]. ...
Pyrenophora teres f. teres (Ptt) is a severe pathogen to spring barley in Northern Europe. Ptt with relevant mutations in fungicide target proteins, sterol 14α-demethylase (CYP51A), cytochrome b (Cyt b), and succinate dehydrogenase (SDH) would put efficient disease control at risk. In the growing seasons of 2021 and 2022, 193 Ptt isolates from Estonia were analysed. In this study, mutation detection and in vitro fungicide sensitivity assays of single-spore isolates were carried out. Reduced sensitivity phenotype to mefentrifluconazole was evident in Ptt isolates with a F489L mutation in CYP51A or with 129 bp insert in the Cyp51A gene-promoter region. However, sensitivity to a prothioconazole-desthio remained high regardless of these molecular changes. The Ptt population was mostly sensitive to bixafen, fluxapyroxad, pyraclostrobin, and azoxystrobin. The sensitivity of fluxapyroxad and bixafen has been affected by two mutations, C-S135R and D-H134R, found in SDH subunits. The F129L mutation in Cyt b influenced azoxystrobin but not pyraclostrobin sensitivity. In total, 30 isolates from five fields had relevant mutations in three target protein genes simultaneously. Most of these isolates had a reduced sensitivity phenotype to mefentrifluconazole, fluxapyroxad, and azoxystrobin, while sensitivity to other tested fungicides remained high. Furthermore, possible sexual reproduction may enhance the pathogen’s fitness and help it adapt to fungicides.
... f. teres Smed.-Pet. (Ptt), the causal agent of net form net blotch (NFNB) disease [1], is an important and widespread pathogen of barley [2,3]. Typical symptoms initiated by this ascomycete fungus can be recognized based on longitudinal and transverse necrotic streaks forming characteristic net-like leaf lesions, which are often surrounded by a chlorotic halo on sensitive host cultivars [1]. ...
... Growing tolerant/resistant cultivars is the most economical and environmentally friendly method of managing plant diseases. Host resistance against NFNB in barley is complicated and can be conferred by both quantitative trait loci and specific major genes [3,[9][10][11][12][13][14][15][16]. Quantitative resistance is effective against a range of Ptt isolates differing in virulence and is best expressed during the adult growth stages under field conditions [10,17,18]. ...
... Qualitative resistance is controlled by major genes specific to certain Ptt pathotypes and is effective in both seedlings and adult plants [19,20]. Major gene resistance to Ptt may follow a gene-for-gene or inverse gene-for-gene model [3] as Ptt produces host-specific toxins [21][22][23], a kind of virulence factor, which is recognized and acts as a necrotrophic effector in toxin-sensitive cultivars [24,25]. Sarpeleh et al. [26] also identified some non-host selective low-molecular weight compounds that induce chlorosis in barley leaves. ...
Pyrenophora teres f. teres (Ptt), the causal agent of net form net blotch (NFNB) disease, is an important and widespread pathogen of barley. This study aimed to quantify and characterize the virulence of Ptt isolates collected from experimental fields of barley in Hungary. Infection responses across 20 barley differentials were obtained from seedling assays of 34 Ptt isolates collected from three Hungarian breeding stations between 2008 and 2018. Twenty-eight Ptt pathotypes were identified. Correspondence analysis followed by hierarchical clustering on the principal components and host-by-pathogen GGE biplots suggested a continuous range of virulence and an absence of specific isolate × barley differential interactions. The isolates were classified into four isolate groups (IG) using agglomerative hierarchical clustering. One IG could be distinguished from other IGs based on avirulence/virulence on one to five barley differentials. Several barley differentials expressed strong resistance against multiple Ptt isolates and may be useful in the development of NFNB-resistant barley cultivars in Hungary. Our results emphasize that the previously developed international barley differential set needs to be improved and adapted to the Hungarian Ptt population. This is the first report on the pathogenic variations of Ptt in Hungary.
... The current taxonomic position of P. teres is as follows: Kingdom: Fungi, Phylum: Ascomycota, Subphylum: Pezizomycotina, Class: Dothideomycetes, Order: Pleosporales, Family: Pleosporaceae, Genus: Pyrenophora, Species: teres (Liu et al. 2011;Kinzer 2015;Backes et al. 2021). This classification is also supported by Marin-Felix et al. (2019), who additionally mention the sub-class Pleosporomycetidae to which the genus Pyrenophora belongs. ...
... As its name, "net blotch", suggests, the disease leads to symptoms resembling a network pattern, mainly on the leaves (Figure 1) but also on other parts of barley, such as leaf sheaths and stems, as well as on flowers and grains (McLean et al. 2009;Liu et al. 2011;Fowler et al. 2017;Backes et al. 2021). The initial symptoms are primarily observed on the leaves of young plants shortly after the winter dormancy period and even during the tilling phase (author's observation). ...
... The symptoms of the net form of the pathogen were first observed in 1920 (Atanasoff & Johnson 1920;Liu et al. 2011;Poudel 2018). On the other hand, the symptoms of the spot form were first noticed in 1963 during the study of net blotch but were considered mutants of the P. teres species (McDonald 1963(McDonald , 1967El-Mor 2016;Poudel 2018). ...
... In agreement with the ABC analyses, we also found evidence for an early divergence between Caucasus and the North African population. Considering a mutation rate (μ) of 5.7 x 10 −7 per base pair [51] and assuming here on average one sexual generation per year [4], these events coincide with the domestication of barley and subsequent migration waves of neolithic farmers to Northwest Africa [52] about 7,000 to 14,500 years ago (Table I in S1 Table). ...
... Group 3 considers North America and Europe to share a common ancestor (scenarios 3,7,10,23,24). Group 4 considers North America and North Africa share a common ancestor (scenarios 4,8,11,13,25). Group 5 considers the North America and the "ghost" population to share a common ancestor (scenarios 5,9,12,14,15). ...
Fungal pathogens cause devastating disease in crops. Understanding the evolutionary origin of pathogens is essential to the prediction of future disease emergence and the potential of pathogens to disperse. The fungus Pyrenophora teres f. teres causes net form net blotch (NFNB), an economically significant disease of barley. In this study, we have used 104 P . teres f. teres genomes from four continents to explore the population structure and demographic history of the fungal pathogen. We showed that P . teres f. teres is structured into populations that tend to be geographically restricted to different regions. Using Multiple Sequentially Markovian Coalescent and machine learning approaches we demonstrated that the demographic history of the pathogen correlates with the history of barley, highlighting the importance of human migration and trade in spreading the pathogen. Exploring signatures of natural selection, we identified several population-specific selective sweeps that colocalized with genomic regions enriched in putative virulence genes, and loci previously identified as determinants of virulence specificities by quantitative trait locus analyses. This reflects rapid adaptation to local hosts and environmental conditions of P . teres f. teres as it spread with barley. Our research highlights how human activities can contribute to the spread of pathogens that significantly impact the productivity of field crops.
... Yield loss due to leaf stripe can reach up to 70%, although in Iran yield losses ranging from 2.5 to 28.4% occur on foundation and certified barley seed fields (Aghnoum 2019). Net blotch can cause potential yield losses from 10% to 40%, while in Iran it can reach up to 35% in epidemic years on susceptible cultivars (Liu et al. 2011). Although previous studies have identified losses in yield of barley, so far, there has been no report from pre-basic barley seed fields. ...
... Fungal pathogens belonging to the Pyrenophora usually penetrate directly through the cuticle into epidermal cells, which is accomplished by the secretion of cell wall degrading enzymes (CWDEs), as well as by pressure generated from the appressorium structures which penetrate cell walls or can enter through natural openings (Liu et al. 2011). Phytopathogens often produce different extracellular CWDEs, as the major type of virulence factors, which are necessary for Pyrenophora pathogens to penetrate into plant cell walls and plasma membranes, and to grow and infect plant tissue (Lightfoot and Able 2010). ...
Plant diseases caused by seed-borne pathogens cause yield and quality losses and threaten seed production of barley (Hordeum vulgare L.) and food security. The aim of this study was to compare common seed health methods for the diagnosis and detection of Pyrenophora species, and to investigate cell wall degrading enzymes (CWDEs), virulence and aggressiveness of the isolates obtained from pre-basic barley seed fields in Iran. Comparing common seed health methods showed that more fungal isolates were recovered from seeds using the agar plate method compared to freezing blotter, osmotic, embryo count, and seed washing tests. A total of 7 fungal species from 5 genera were identified from 30 different samples of various Iranian barley cultivars. Based on morphological and molecular characteristics, the fungi were identified as Pyrenophora graminea, P. teres f. teres, P. teres f. maculata, Alternaria alternata, Fusarium culmorum, F. graminearum, Rhynchosporium commune and Ustilago nuda f. sp. hordei. This study has shown that barley seed samples carry a wide diversity of fungi. The results showed that the 57 % of the total samples were found to be infected by seed-borne fungi. Among the genera, Pyrenophora was the most abundant fungus. Diverse levels of virulence and aggressiveness were observed for various isolates of Pyrenophora species. Analyzing the activity of CWDEs produced by isolates revealed that xylanase activity was more important than cellulase activity for the virulence of Pyrenophora isolates and enzyme activities affect levels of virulence and aggressiveness of isolates. Therefore, these findings suggest that activity levels of xylanase are correlated with variation in virulence and aggressiveness of Pyrenophora isolates on seedings. This is the first report identifying the seed-borne fungi of Iranian barley cultivars in pre-basic barley seed fields of Iran.
... The causal pathogen of net blotch is Pyrenophora teres, which can be further classified into two different forms: P. teres f. teres and P. teres f. maculata, distinguished by the type of the lesions they induce on barley leaves. Similar to Z. tritici, P. teres is also a hemibiotrophic pathogen, but it exhibits shorter biotrophic and incubation periods (Liu et al. 2011;Backes et al. 2021b). ...
Wheat and barley rank among the main crops cultivated on a global scale, providing the essential nutritional foundation for both humans and animals. Nevertheless, these crops are vulnerable to several fungal diseases, such as Septoria tritici blotch and net blotch, which significantly reduce yields by adversely affecting leaves and grain quality. To mitigate the effect of these diseases, chemical fungicides have proven to be genuinely effective; however, they impose a serious environmental burden. Currently, biocontrol agents have attracted attention as a sustainable alternative to fungicides, offering an eco-friendly option. The study aimed to assess the efficacy of Bacillus velezensis BE2 in reducing disease symptoms caused by Zymoseptoria tritici and Pyrenophora teres. This bacterium exhibited significant antagonistic effects in vitro by suppressing fungal development when pathogens and the beneficial strain were in direct confrontation. These findings were subsequently confirmed through microscopic analysis, which illustrated the strain’s capacity to inhibit spore germination and mycelial growth in both pathogens. Additionally, the study analysed the cell-free supernatant of the bacterium using UPLC-MS (ultra-performance liquid chromatography-mass spectrometry). The results revealed that strain BE2 produces, among other metabolites, different families of cyclic lipopeptides that may be involved in biocontrol. Furthermore, the beneficial effects of strain BE2 in planta were assessed by quantifying the fungal DNA content directly at the leaf level after bacterization, using two different application methods (foliar and drenching). The results indicated that applying the beneficial bacterium at the root level significantly reduced pathogens pressure. Finally, gene expression analysis of different markers showed that BE2 application induced a priming effect within the first hours after infection.
Key points
• BE2 managed Z. tritici and P. teres by direct antagonism and induced systemic resistance.
• Strain BE2 produced seven metabolite families, including three cyclic lipopeptides.
• Application of strain BE2 at the root level triggered plant defense mechanisms.
... The NBNF disease is a destructive disease of barley that causes important yield losses in susceptible cultivars. Ptt can colonise the host by producing necrotic and chlorotic symptoms due to net blotch in plant tissue [5,38,39]. In susceptible barley cultivars, germinated conidia produce the appressorium through the plant membrane at 1 d.p.i. ...
Necrotrophic fungi affect a wide range of plants and cause significant crop losses. For the activation of multi-layered innate immune defences, plants can be primed or pre-conditioned to rapidly and more efficiently counteract this pathogen. Untargeted and targeted metabolomics analyses were applied to elucidate the biochemical processes involved in the response of 3,5-dichloroanthranilic acid (3,5-DCAA) primed barley plants to Pyrenophora teres f. teres (Ptt). A susceptible barley cultivar (‘Hessekwa’) at the third leaf growth stage was treated with 3,5-DCAA 24 h prior to infection using a Ptt conidia suspension. The infection was monitored over 2, 4, and 6 days post-inoculation. For untargeted studies, ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC–MS) was used to analyse methanolic plant extracts. Acquired data were processed to generate the data matrices utilised in chemometric modelling and multi-dimensional data mining. For targeted studies, selected metabolites from the amino acids, phenolic acids, and alkaloids classes were quantified using multiple reaction monitoring (MRM) mass spectrometry. 3,5-DCAA was effective as a priming agent in delaying the onset and intensity of symptoms but could not prevent the progression of the disease. Unsupervised learning methods revealed clear differences between the sample extracts from the control plants and the infected plants. Both orthogonal projection to latent structure-discriminant analysis (OPLS-DA) and ‘shared and unique structures’ (SUS) plots allowed for the extraction of potential markers of the primed and naïve plant responses to Ptt. These include classes of organic acids, fatty acids, amino acids, phenolic acids, and derivatives and flavonoids. Among these, 5-oxo-proline and citric acid were notable as priming response-related metabolites. Metabolites from the tricarboxylic acid pathway were only discriminant in the primed plant infected with Ptt. Furthermore, the quantification of targeted metabolites revealed that hydroxycinnamic acids were significantly more prominent in the primed infected plants, especially at 2 d.p.i. Our research advances efforts to better understand regulated and reprogrammed metabolic responses that constitute defence priming in barley against Ptt.
... The disease can cause yield losses estimated at 20-40% on average, [6][7][8][9][10] and up to 100% in highly susceptible barley varieties. 11 Some of the most affected yield components are the number of grains per unit area and the weight of the grains. The pathogen also causes a decrease in malt extract, which affects the malting quality for brewing. ...
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.
