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Tan spot disease of wheat (also known as yellow spot) is caused by the necrotrophic fungal pathogen Pyrenophora tritici‐repentis (Ptr). Initially described as a grass pathogen, Ptr has become a wheat pathogen of global importance. In Australia, tan spot was first recorded in 1952 as a minor wheat disease. However, by the 1970s tan spot had reached epidemic levels in Australia with yield losses of up to 49% reported in the north‐eastern region. A national survey carried out in 2007/2008 placed tan spot as the most economically important wheat disease with an estimated yield loss of 6%, corresponding to nearly a quarter of all disease losses. The incidence of tan spot in Australia has now markedly reduced with some wheat breeding programmes no longer considering tan spot disease resistance to be a priority trait. The disease can be effectively managed with integrated control strategies such as crop rotation, timely application of fungicides and removal of surface stubble. However, the key to the success of controlling tan spot disease in Australia has been achieved through wheat breeding programmes. The development of tan spot resistance resources suitable for the Australian climate was a concerted effort between national and international research organizations and Australian wheat breeders, supported by the Australian Grains Research Development Corporation (GRDC). While traditional breeding was essential to combat the disease, this article highlights the value of effector biology in assisting the development of resistant cultivars. [ABSTRACT FROM AUTHOR]

The resistance gene Lr34 conditions durable disease resistance to many biotrophic wheat pathogens and has been incorporated into many wheat cultivars throughout the world. Lr67 is a similar adult plant resistance gene that also conditions resistance to multiple wheat diseases. Both genes significantly reduce disease severity and work in an additive manner with other rust resistance genes. To determine the effect of Lr34 and Lr67 on Fusarium head blight (FHB), two doubled haploid populations, segregating for each of these genes, were developed in the Thatcher wheat background by crossing near‐isogenic lines. Progeny from these populations were tested in five Fusarium graminearum‐inoculated disease nurseries and assessed for FHB symptoms, using a visual rating index (VRI), and deoxynivalenol (DON) accumulation. Both Lr34 and Lr67 significantly reduced visual symptoms of FHB and DON overall, though those effects were not significant in all environments. The overall reduction in the group of progeny with the resistant allele compared to the group with the susceptible allele for VRI was 9.4% for Lr34 and 6.8% for Lr67, while for DON it was 16.4% for Lr34 and 14.9% for Lr67. These genes represent important tools for improving resistance to FHB and many other diseases in wheat. [ABSTRACT FROM AUTHOR]

The importance of monitoring and management of yellow rust, caused by Puccinia striiformis f. sp. tritici (Pst), has markedly increased in Russia over recent years because of intensifying negative effects of this destructive disease on wheat production. The Pst virulence survey was conducted in 2019–2021 in the European (North‐West, Volga, North Caucasus) and Asian (Siberia) parts of Russia, and the same 109 isolates have been genotyped here with 20 SSR markers. Fifty‐three multilocus genotypes (MLGs) were detected, seven of which occurred in two or more regions. The most frequent MLG was found in three European Pst collections (except Dagestan) and Siberia. SSR‐based variation within the regional collections was low because many MLGs were closely related. Nevertheless, each collection contained relatively different small genotype groups. No clear geographic structure of the Russian Pst population was observed because the five studied regional collections shared groups of similar genotypes. The most singular SSR genotype was identified in the North‐West collection, but genotypes of four invasive isolates belonging to the PstS2 temperature‐adapted aggressive strain did not considerably differ from others. The observed heterozygosity at all SSR loci exceeded the expected one in all regional Pst collections, which could imply asexual reproduction of the pathogen. Both the SSR and virulence analyses demonstrated similar patterns of relationships between the regional Pst collections, although the magnitude of differences between the collections was larger for virulence pathotypes. However, no significant association was established between the virulence pathotypes and SSR genotypes because multiple pathotypes had the same genotype and vice versa. [ABSTRACT FROM AUTHOR]

The cultivation of wheat in North America represents a relatively recent endeavour, spanning a mere 150 years. This relatively brief period of its recent cultivation has allowed the opportunity to document the threats and diseases farmers had to face from the start. In this minireview, our primary objective is to provide a detailed exploration of the historical context on how we end up effectively managing what was once among the most destructive and hard to manage diseases affecting wheat, namely, common bunt (covered smut). This review delves into the early research efforts dedicated to understanding the biology of the causal pathogens and developing effective management approaches. These efforts encompass a wide spectrum of potential methods, ranging from seed treatments to cropping practices, and the development of genetic resistance. Throughout this exploration, we will also spotlight the remarkable scientific success story that has unfolded within the Canadian context. In essence, this review aims to provide a scientific examination of the history, challenges and innovative approaches associated with mitigating the impact of bunt pathogens on wheat cultivation in North America, and future challenges. [ABSTRACT FROM AUTHOR]

Cultivar resistance is a major asset for the management of crop diseases and can play an important role in agroecological transition. However, the wide deployment of a reduced number of resistance genes can lead to a rapid adaptation of pathogen populations and to a loss of resistance efficiency. The objective of this study was to characterize and discuss different trajectories of adult plant ratings for resistance to yellow rust in French wheat cultivars between 1963 and 2018. Among 719 cultivars assessed for at least 2 years, 590 cultivars showed no variation in their resistance scores, despite a mean of 4.3 years and up to 33 years of assessment. A set of descriptive variables was computed in order to compare the evolution of resistance score of 129 cultivars that experienced resistance variation. We applied a principal component analysis and a hierarchical clustering on principal components to this subdataset to constitute clusters corresponding to different cultivar profiles. Clusters C1 and C2 had small resistance variations (1–2 points on a 1–9 scale); Cluster C3 had long assessment durations and several small drops in resistance score and could be associated with quantitative resistance erosion; Cluster C4 included major drops in resistance score (4–5 points), often associated with known breakdowns of major resistance genes. Cases of limited drops in resistance score as a known resistance gene was broken down suggest the presence of efficient adult plant resistance. We discuss the use of information extracted from this dataset and methods to further explore sources of resistance to yellow rust present in French cultivars. [ABSTRACT FROM AUTHOR]

The genus Clavibacter (family Microbacteriaceae) includes gram‐positive actinobacterial species infecting diverse agricultural crops such as alfalfa, maize, pepper, potato, tomato and wheat. Clavibacter tessellarius, causing bacterial mosaic of wheat, was reported for the first time in 1976 in Nebraska (United States). Since then, the pathogen was thought to be restricted to North America (Canada and the United States). While bacterial strains suspected to be C. tessellarius have occasionally been isolated from wheat samples outside North America, occurrence of the pathogen in the Old World has not yet been confirmed by the plant protection authorities. In spring 2020 (January to May) dozens of wheat fields with young plants showing leaf chlorosis and mild mosaic symptoms were surveyed and sampled in southern Iran. Among 192 surveyed wheat fields, gram‐positive, orange‐pigmented actinobacterial strains were isolated from samples of 53 fields. Altogether, 61 bacterial strains were identified as C. tessellarius based on the phenotypic features, PCR‐based molecular tests and pathogenicity assays. Multilocus sequence analysis of five housekeeping genes (atpD, dnaK, gyrB, ppk and rpoB) using 10 representative strains from diverse geographic areas in southern Iran confirmed the phylogenetic status of the strains within C. tessellarius. Our data indicate that the bacterial mosaic pathogen occurs in four southern Iranian provinces including Bushehr, Fars, Kerman and Khuzestan. Thus, occurrence of C. tessellarius outside North America is confirmed. Potential risks associated with the emergence of the pathogen in the Old World, and the need for strict quarantine measures in the area, is further discussed. [ABSTRACT FROM AUTHOR]

Monitoring virulent strains within pathogen populations is crucial to improve host resistance deployment strategies. Such monitoring increasingly involves field pathogenomics studies of molecular polymorphisms in pathogen genomes based on high‐throughput screening technologies. However, it is not always straightforward to predict virulence phenotypes from these polymorphisms, and in planta phenotyping remains necessary. We developed a method for 'bulk phenotyping on checkerboard microcanopies of wheat near‐isogenic lines' (BPC) for estimating the frequency of virulence against a resistance gene in mixed populations of the fungal pathogen Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB) in wheat, without the need for strain‐by‐strain pathogen phenotyping. Our method involves the uniform inoculation of a microcanopy of two wheat lines—one with the target resistance gene and the other without it—with a multistrain mixture of isolates representative of the population to be characterized, followed by the differential quantification of infection points (lesions). Using Stb16q, a wheat resistance gene that has recently broken down in Europe, we found a robust correlation between the ratio of the mean number of lesions on each wheat line and the frequency of virulent strains in the inoculum. Using pairs of virulent and avirulent strains, as well as synthetic populations consisting of 10 virulent strains and 10 avirulent strains mixed in different proportions, we validated the principle of the method and established standard curves at virulence frequencies close to those observed in natural conditions. We discuss the potential of this method for virulence monitoring in combination with molecular methods. [ABSTRACT FROM AUTHOR]

Many factors are known to influence infection by cereal rusts, including environmental variables such at light, humidity and temperature, the topography of the leaf surface, as well as plant volatiles. However, few studies have aimed to link these factors. Previously, the quantity of light received by wheat seedlings prior to inoculation with Puccinia striiformis f. sp. tritici (Pst) urediniospores was shown to influence yellow rust infection efficiency. In this study we show that germination and the ability of germlings (germinated urediniospores) to enter stomata is enhanced on wheat seedlings subjected to high quantities of light pre‐inoculation with Pst urediniospores, while on seedlings exposed to a long dark period germination and infection were compromised. Using headspace collections and gas chromatography–mass spectrometry (GC–MS) analysis thereof, we link this effect of high light quantity to quantitative changes in the profile of volatile organic compounds (VOCs). We show that the VOCs within headspace collections from wheat seedlings exposed to high quantities of light were able to support greater levels of Pst urediniospore germination than the headspace collections from wheat seedlings exposed to a period of dark. In vitro analysis of individual VOCs identified compounds that enhanced Pst urediniospore germination. These VOCs included the sesquiterpene caryophyllene, the monoterpene α‐pinene, the fatty acid α‐linolenic acid, the organic alcohols 1‐hexanol, 3‐hexen‐1‐ol and 5‐hexen‐1‐ol, the aldehyde cis‐3‐hexenal and the ester hexyl acetate. [ABSTRACT FROM AUTHOR]

Alternaria is an important toxigenic fungal genus endangering the quality of cereal grains. No data are available in the literature regarding the composition of Alternaria species in wheat from the main wheat‐cultivating regions of China. In this study, a total of 282 strains were isolated from wheat kernels collected in various provinces. Phylogenetic characterization was performed using two informative loci, ASA10 and ASA19, demonstrating that all strains belonged to A. alternata. A low molecular diversity was observed, which did not appear to be influenced by geographic origin. The secondary metabolite profile of the strains was evaluated in rice culture. Altertoxin I was synthesized at a high concentration by the majority of the strains, while the accumulation of altenuene was lower in both frequency and level than that of alternariol and its derivative. A. alternata did not cause readily observable symptoms on wheat spikes after spraying of the conidia at anthesis, but a higher quantity of altertoxin I and Alternaria DNA were detected in inoculated grains. Artificial inoculations of apple fruit showed that all examined strains were capable of causing typical rot symptoms and producing all four toxins to a certain degree. The widespread occurrence of A. alternata on wheat grains and its ability to synthesize various toxic metabolites may pose a serious hazard for both growers and consumers. [ABSTRACT FROM AUTHOR]

Leaf rust, caused by Puccinia triticina (Pt), is a major disease of wheat and a significant problem for wheat production in Brazil. The Brazilian variety Toropi, released in 1965, has maintained high levels of field, adult plant resistance (APR) to leaf rust across global locations, while microscopic studies have indicated prehaustorial resistance mechanisms. Analyses of gene expression in flag leaves of Toropi, during the early stages of Pt infection, were undertaken to explore the mechanisms behind the APR in Toropi. Differential expression of wheat genes was undertaken, comparing Pt‐ to mock‐inoculated and Pt‐ to Pt‐inoculated time points. Analysis of gene expression indicated a strong response to Pt, which was fully active by 6 h after inoculation (hai). More genes were downregulated than upregulated, particularly at 6 and 12 hai. Gene Ontology enrichment analysis indicated a shutting down of RNA and protein synthesis and an early effect on photosynthesis, with disruption of the electron transfer chain. Analyses of upregulated genes identified genes involved in ATP‐binding and protein kinase activity at 6 hai, supporting a rapid metabolic response to Pt infection. A general upregulation of genes involved in transport and metabolism indicated the need to relocate protein and organic‐based resources. Alignment of differentially expressed genes with the genomic regions defining four leaf rust APR quantitative trait loci (QTLs) in Toropi identified candidate resistance genes, including a sugar transporter, a receptor kinase and a seven‐transmembrane MLO family protein. In addition, 60 Pt genes were identified, 11 being annotated as potential effector proteins. [ABSTRACT FROM AUTHOR]

Wheat stripe mosaic virus (WhSMV) is the causal agent of soilborne wheat mosaic disease (SBWMD) in Brazil, which is a serious threat to wheat production in the southern part of the country. WhSMV also occurs in Paraguay and South Africa. The virus is soilborne, transmitted by Polymyxa graminis, and management strategies are mainly based on genetic resistance. Variation in the reaction (type and severity of symptoms) of cultivars has been reported depending on the region and/or year of cultivation, leading wheat breeding programmes to test their materials in several locations, which increases costs and is time‐consuming. One hypothesis is that this variation in symptoms is a result of the genetic variability of WhSMV. We assessed the genetic variability and population structure of WhSMV infecting wheat in Brazil and South Africa. In field experiments conducted in different locations in southern Brazil, a consistent reproducibility of symptoms was observed in a set of cultivars, and molecular analysis showed a low degree of genetic variability of the Brazilian viral population. The hypothesis that the variation in SBWMD symptoms in Brazil is due to genetic variability of the virus was thus rejected. Comparison of the Brazilian and South African WhSMV isolates indicated that they comprise distinct subpopulations and that the Brazilian subpopulation is more variable than the South African subpopulation. The lower genetic variability of the South African subpopulation suggests genetic stability or a recent emergence of WhSMV in that region. [ABSTRACT FROM AUTHOR]

Crown rot (CR; Fusarium pseudograminearum) is a serious disease in winter cereals. Soil type, temperature, nutrients, water availability and stubble‐borne inoculum levels play major roles in determining disease severity. This paper reports the impact of two different watering regimes on the disease severity and gas exchange of F. pseudograminearum infected bread wheat for the first time. Fusarium pseudograminearum inoculated and noninoculated genotypes with different susceptibility to CR were watered to either field capacity or a reduced watering regime in three controlled environment experiments. Rate of photosynthesis, stomatal conductance, internal CO2 concentration and transpiration rate were measured using a portable photosynthesis system, together with disease severity of leaf sheaths at 28 days after planting. Significant differences in disease severity were reported between watering treatments with reduction in CR symptoms in the partially resistant genotypes in the reduced water treatment. Photosynthesis, stomatal conductance and transpiration rate were significantly decreased across most genotypes when inoculated with F. pseudograminearum. Differences in gas exchange between inoculum treatments were more evident in plants watered to field capacity. Water availability has been reported to be one of the crucial factors for initiating F. pseudograminearum infection and subsequent development of CR disease. This research demonstrates significant variation in genotype‐related responses to the complex interactions of F. pseudograminearum infection and water treatment, with a negative impact of both limited soil water availability and CR disease severity on plant gas exchange in bread wheat. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is one of the most devastating crop diseases worldwide, significantly reducing the yield and quality of small‐cereal crops such as wheat and barley when favourable weather conditions exist during anthesis. Additionally, FHB‐associated mycotoxins significantly impact global food and feed safety. Controlling FHB with fungicides applied near anthesis reduces visual FHB symptoms and associated mycotoxin production, thereby lowering disease‐related costs. However, when weather conditions are unfavourable for FHB occurrence, fungicide application can be costly and environmentally undesirable. Thus, fungicides should be used sparingly only when the pathogen is present and weather conditions are favourable. Modelling of FHB risk using weather data has grown rapidly in recent decades and plays an essential role in integrated crop disease management. In this review, several weather‐based FHB models are selected and described in detail. The models were developed globally for assessing the real‐time risk of FHB epidemics in various regions/countries. Most of these models are site‐specific and predict FHB visual observations such as the incidence and severity of FHB, Fusarium‐damaged kernels (FDK), and also deoxynivalenol (DON) levels. The review also highlights the limitations of these existing models, including their narrow applicability, low accuracy for high‐risk contamination situations, and omissions of certain factors. Also discussed are potential avenues for improvement and enhanced predictive capabilities including consideration of additional disease risk factors as well as a broader range of varieties. These predictive models can assist producers, regulatory agencies, and industry to mitigate potential food and feed security and safety concerns. [ABSTRACT FROM AUTHOR]

The article emphasizes the need for expanding the differential sets used in race typing experiments for plant pathologists to provide valuable information to plant breeders. Specifically focusing on stripe rust, a fungal disease that affects wheat crops, the article explains how the pathogen evolves and gains virulence over time, necessitating the continuous introgression of resistance from different sources. The article also highlights the importance of including relevant differential genotypes in race typing experiments to support the development of resistant cultivars. Additionally, the document provides a list of wheat cultivars and their corresponding resistance genes to stripe rust, along with discussing the significance of standardizing race typing conditions for more accurate and comparable results in studying the population dynamics of the stripe rust pathogen in North America. [Extracted from the article]

Wheat leaf rust, caused by Puccinia triticina, is reported annually in southern Russia, the main wheat production region in Russia. The effect of biotic (types of cultivar resistance) and abiotic (northern, central and southern agro‐ecological zones) factors on virulence variability of the pathogen was analysed with 43 Lr differentials. Virulence frequencies to Lr genes 1, 2c, 3, 3bg, 11, 14a, 14b, 16, 17, 18, 23, 25, 26, 33, 34, 40 and Kanr exceeded 50% in all populations. A total of 81 virulence phenotypes (based on the standard set of 20 differentials) were identified among 108 isolates. The most common phenotypes were PHSTQ, THTTR, PHTTR and TKTTR. The minimum genetic distance (the highest similarity) was established between the P. triticina populations from susceptible cv. Krasnodarskaya 99 and cv. Brigada with race‐specific resistance. P. triticina populations from the susceptible cultivar in the three agro‐ecological zones were less variable and more similar than the cultivar‐specific and natural pathogen populations. Resistance types of host cultivars seem to have a greater effect on the pathogen population than abiotic factors. Nevertheless, abiotic factors need to be considered when making decisions about deployment of wheat varieties. Our results support the paradigm of a shift in the population of an obligate parasite towards increased virulence in response to the selection pressure of cultivars with race‐specific resistance. [ABSTRACT FROM AUTHOR]

Common root rot (CRR) caused by the soilborne pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus) is becoming increasingly prevalent worldwide. Identification of CRR is difficult and time‐consuming for human assessors due to the non‐distinctive above‐ground symptoms, with browning of subcrown internodes and roots the most distinguishing symptom of infection. CRR disease has been recognized as a significant disease for cereal crops in many countries. In 2009, CRR in Australia was estimated to cause $30 million average annual yield loss for wheat and $13 million for barley. Recent evidence indicates CRR may be more prevalent than expected in Australian wheat cropping areas due to lack of research on this disease. Low levels of B. sorokiniana survive in the soil for up to 10 years and attack plants at early stages of growth. Therefore, mitigating CRR in wheat and barley may not be practical at the late stages of infection due to lack of effective methods; however, early detection might be viable to alleviate the impact of this disease. A comprehensive overview of CRR caused by B. sorokiniana, including disease background, worldwide economic losses, management methods, potential CRR detection using multispectral and hyperspectral sensors and the research focus over the past 50 years is provided in this article. This review paper is expected to provide thorough supplemental information for current studies about CRR and proposes recommendations for whole‐of‐field disease scouting methods to farmers, enabling reduced time and cost for CRR management and increasing wheat and barley production worldwide. [ABSTRACT FROM AUTHOR]

To enhance the framework of the mechanisms of action used by Trichoderma gamsii T6085 for the control of Fusarium head blight (FHB), this work investigated its ability to modulate the expression of defence‐related genes of wheat (Triticum aestivum 'Apogee') in response to endophytic colonization of plant tissues. Changes in relative expression of pal1, pr1, pgip2 and lox1 genes were assessed over time in wheat roots, in spikes colonized by T6085 alone and both T6085 and Fusarium graminearum, and in leaves from wheat seedlings root‐inoculated with T6085. Results indicate the ability of T6085 to induce local and systemic defence responses in wheat plants in the presence of one of the causal agents of FHB. There was a general significant up‐regulation of the plant defence‐related genes analysed, especially in the first days after the application of T6085. According to these results, modulation of plant defence genes could be included within the arsenal of mechanisms used by T6085 when applied to wheat, an additional feature of interest in the management of FHB. To evaluate the effect of the plant genotype on the ability of T6085 to endophytically colonize roots, root colonization was assessed on four cultivars of T. aestivum and two cultivars of T. durum. Data showed that roots of only two T. aestivum cultivars were endophytically colonized by T6085, similar to cv. Apogee used here as control, thus demonstrating an effect of the host genotype on the endophytic ability of T6085. [ABSTRACT FROM AUTHOR]

Zymoseptoria tritici is the causal fungus of Septoria tritici blotch (STB), a globally important foliar disease of wheat. Infections by more than one strain of a pathogen, or co‐infections, are known to be the most prevalent form of infection in the field. The impact that co‐infection of Z. tritici has on disease severity for the plant host and its effect on plant defence are not fully understood. Here, isolates of Z. tritici were extracted from STB‐presenting leaves from UK sites. Disease assays comparing single‐isolate inocula to mixed inocula were carried out on three cultivars of wheat, Flame, Stigg and Longbow. Leaves infected with mixed inocula were found to show low disease symptoms, including lesion and pycnidial coverage, compared with those infected with single isolates. Growing mixed isolates together in liquid media did not reveal evidence of competition or decreased growth compared with single‐isolate inocula. Wheat infected with a mixture of at least two Z. tritici isolates (of differing aggressiveness) could induce Pr‐1 (Pathogenesis‐related 1) at a significantly higher level in distal uninfected leaves compared with distal leaves of plants infected with a single aggressive isolate. Expression of Pr‐1 in plants with mixed inocula was intermediate to plants infected with an aggressive isolate (lower expression) and plants infected with a less aggressive isolate (higher expression). This suggests that wheat undergoes systemic "sensitization" by the least aggressive Z. tritici isolate during co‐infection. [ABSTRACT FROM AUTHOR]

Research to identify appropriate biological agents for controlling pathogens might exploit experimental evolution to select for enhanced antagonism against pathogens. We developed an experimental regime facilitating this approach, featuring the bacterial broad‐spectrum predator Myxococcus xanthus and the fungal wheat pathogen Zymoseptoria tritici. We demonstrate that Z. tritici, a major cause of crop loss and fungicide use worldwide, both fuels growth of and is killed by M. xanthus on wheat straw, a probable source of seedling infection. M. xanthus was found capable of growth on moistened straw alone, unaided by Z. tritici, in a manner dependent on both M. xanthus initial density and on how long straw was moistened before M. xanthus inoculation. Such growth of non‐cellulolytic myxobacteria on plant detritus may have implications for understanding their roles in nutrient cycling. However, straw with Z. tritici was found to fuel greater M. xanthus growth than straw alone under many conditions. After shorter moistening periods, growth by low‐density M. xanthus populations was found to be fully dependent on Z. tritici. Such pathogen‐dependent M. xanthus populations could be sustained with population replacement over five 1‐week growth cycles, indicating the feasibility of conducting long‐term experimental evolution with this system. Furthermore, M. xanthus was found to kill majorities of Z. tritici populations on both buffered agar and straw. Our results suggest that myxobacteria may serve as effective biocontrol agents of Z. tritici and are amenable to long‐term experimental selection for enhanced killing of this pathogen, an approach broadly applicable to many potential biocontrol agents and target pathogens. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch caused by Zymoseptoria tritici is a serious threat to wheat in Tunisia, causing yield losses of up to 50%. Epidemics occur regularly, mainly on durum wheat (DW) but also to a lesser extent on bread wheat (BW), that are mainly cropped in the north‐western and north‐eastern regions, respectively. Isolates of Z. tritici exhibit both cultivar specificity and host species specificity. In this study, we investigated the extent of host specialization of Z. tritici in the Tunisian context. Cross‐inoculations of different strains derived from either BW or DW were performed at the seedling stage on a panel of the most cultivated BW and DW varieties in Tunisia using the percentage of pycnidia coverage and necrotic leaf area as disease parameters. Results showed that the effect of strains, the strain‐derived species, the wheat species and of their interactions were highly significant based on pycnidia coverage. This indicates the presence of significant virulence variability among Z. tritici strains on the tested wheat genotypes, with some strains being more virulent than others. It also suggests cultivar and host species specificity, as not only genotypes of the strains interacted differently with the genotypes of the host, but also the origin of the strain, whether BW or DW, influenced the disease outcome. Hence, future research based on comparative genomics coupled with transcriptomics of these strains and their progenies could determine genes whose expression control this host specificity or is influenced by host or strain genotype, or alternatively by life cycle stage. [ABSTRACT FROM AUTHOR]

Wheat yellow rust (YR) is a most devastating disease in wheat worldwide. In recent years, the epidemic in China has expanded from traditional areas to the middle and lower reaches of the Yangtze River due to the changes in climate and cropping systems. To facilitate YR resistance breeding, it is meaningful to explore resistance loci from local germplasm resources. In this study, a linkage mapping was performed in a recombinant inbred line (RIL) population derived from Ningmai 9 × Yangmai 158 using a high‐density genetic map and phenotypic identification for adult plant resistance (APR) to YR in four environments. Phenotypic analysis showed that Yangmai 158 had better APR than Ningmai 9. Disease severity in different environments was significantly correlated with each other, and it was found that disease severity was significantly influenced by genotype, environment and their interaction. A total of 19 quantitative trait loci (QTLs) were identified, of which four could be detected in multiple environments and four corresponding KASP markers were then developed. Lines with different QTLs from the population including 476 chromosome segment substitution lines (CSSLs) were evaluated for APR. The results revealed that Qyr‐4B.4 and Qyr‐5B.2 could significantly reduce the disease severity, with their combination showing a better effect. The findings of the study can be beneficial for wheat YR resistance breeding in the middle and lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Crop diseases can cause major yield losses, so the ability to detect and identify them in their early stages is important for disease control. Deep learning methods have shown promise in classifying multiple diseases; however, many studies do not use datasets that represent real field conditions, necessitating either further image processing or reducing their applicability. In this paper, we present a dataset of wheat images taken in real growth situations, including both field and glasshouse conditions, with five categories: healthy plants and four foliar diseases, yellow rust, brown rust, powdery mildew and Septoria leaf blotch. This dataset was used to train a deep learning model. The resulting model, named CerealConv, reached a 97.05% classification accuracy. When tested against trained pathologists on a subset of images from the larger dataset, the model delivered an accuracy score 2% higher than the best‐performing pathologist. Image masks were used to show that the model was using the correct information to drive its classifications. These results show that deep learning networks are a viable tool for disease detection and classification in the field, and disease quantification is a logical next step. [ABSTRACT FROM AUTHOR]

Fungicides play an important role in wheat blast management in Brazil. To determine whether the reported patterns of fungicide resistance are present in Pyricularia oryzae populations from wheat and signal grass grown in Minas Gerais state, Brazil, we characterized the sensitivity of a contemporary collection (2018 and 2019) of 64 fungal isolates to seven fungicides belonging to DMI (tebuconazole and epoxiconazole), QoI (azoxystrobin and pyraclostrobin) and SDHI (bixafen, fluxapyroxad and benzovindiflupyr) groups. We further assessed if the differential sensitivity of selected isolates affected disease control using commercial doses of the fungicides applied protectively (prior to inoculation) on the heads of potted plants. Despite finding relatively low levels of in vitro sensitivity to some of the fungicides (e.g., azoxystrobin, fluxapyroxad and bixafen), control efficacies (percentage reductions in head blast severity) were significantly higher than the untreated plants and not affected by the sensitivity of the strain to all fungicides but azoxystrobin. The levels of head blast control for some of the fungicides (>70%) in the greenhouse were similar to or higher than previously reported in the field. The molecular data for a set of isolates representing different fungicide sensitivity levels were generally not predictive of the phenotype. The wheat‐infecting isolates were less sensitive than signal grass‐infecting isolates to all fungicides including azoxystrobin. Our study not only confirms previous reports of low sensitivity to some fungicides, but it also suggests options among site‐specific fungicides, most notably tebuconazole and benzovindiflupyr, that can still be used under an antiresistance strategy such as coformulation with multisite fungicides. [ABSTRACT FROM AUTHOR]

Root‐lesion nematodes (RLNs) Pratylenchus thornei and P. neglectus are globally important pathogens of cereal and pulse crops. These RLNs can occur together in farming systems and must be managed concurrently to minimize substantial yield losses in intolerant crop cultivars. Australian wheat cultivars with resistance to P. neglectus, have either the Rlnn1 resistance gene, which provides a high level of resistance but is linked with yellow flour colour that reduces cultivar marketability for bread production, or QRlnn.lrc‐2B, which provides moderate resistance. We evaluated a collection of 91 P. thornei‐resistant Iranian landrace wheats (ILWs) for their resistance to P. neglectus in four glasshouse experiments to (a) identify genotypes with resistance to both RLNs, (b) determine if any genotypes carried Rlnn1 and/or QRlnn.lrc‐2B and (c) develop ILW‐derived advanced breeding lines (ABLs) with resistance to both RLNs. A factor analytic linear mixed model (FA‐1) that explained 70% of the genetic variation, where the genetic correlations between the experiments ranged from 0.54 to 0.77, was used for the combined analysis of all experiments. Seven P. neglectus‐resistant genotypes were identified, with five that had potentially novel resistance. Subsequently, six breeding lines that were resistant to both RLNs were developed by crossing six ILWs with Australian cultivars and selecting for resistance in each generation. Both the ILWs and ABLs will be valuable genetic resources for wheat breeders to develop cultivars with dual resistance, enabling better management of mixed RLN populations with novel P. neglectus resistance that potentially is not linked with yellow flour colour. [ABSTRACT FROM AUTHOR]

The goals of this study were to evaluate the role of salicylic acid (SA) in causing autotoxic stress in the faba bean root system and explore how the co‐culture of faba bean (Vicia faba) with wheat (Triticum aestivum) alleviates this stress. We designed a hydroponic pot experiment to study the effects of exogenous SA on the occurrence of Fusarium wilt, seedling growth, physiological resistance of faba bean and pathogenicity of Fusarium oxysporum f. sp. fabae (FOF). The results showed that SA significantly increased the incidence and disease index of faba bean Fusarium wilt, inhibited the growth of seedlings and reduced the physiological resistance of faba bean. An in vitro study of FOF found that SA increased the ability of the organism to produce fusaric acid, cellulase and pectinase, which increased the susceptibility of faba bean to Fusarium wilt. Interestingly, co‐cultivation with wheat significantly reduced the content of SA in exudates from the faba bean roots, which directly reduced the deleterious effects of SA. In addition, co‐cultivation could increase the activity of peroxidase and catalase, reduce the content of malondialdehyde, thus improving the ability of faba bean to defend itself. In conclusion, we found that SA, as an autotoxic substance, aggravates the occurrence of Fusarium wilt on faba bean and affects the growth of this crop. However, co‐cultivation of faba bean with wheat could alleviate this autotoxicity. This study has discovered a possible mechanism that could explain how co‐cultivation can alleviate the obstacles in cropping systems and control Fusarium wilt. [ABSTRACT FROM AUTHOR]

The worldwide spread of wheat yellow rust lineage PstS1/S2 adapted to higher temperatures prompted us to investigate how diverse temperature responses of this lineage are in the Middle East, where diversity was previously observed within this lineage for pathotypes and genotypes. Here we highlight the diversity of response to temperature within a PstS1/S2 population. Twenty‐six isolates from eight countries and different altitudes, which were tested under four combinations of cold and warm incubation and postincubation temperature conditions, showed diversity for infection efficiency (IE) and latency period (LP). IE of the various isolates ranged from 5.8% to 13.7% under cold (5°C) and 0.04% to 1% under warm (20°C) incubation temperatures. LP varied from 10.2 days under warm to 4.43 days under cold incubation. LP of isolates from the same country could differ by 2 days. Significant differences in thermal aptitudes of the isolates were observed between and within countries. IE and LP diversity was not related to altitude origin of the isolates on the whole; however, a trade‐off between IE and LP was observed for isolates from low altitude (<400 m) under a warm regime. We showed diversity for thermal aptitude for IE and LP of isolates belonging to the same PstS1/S2 lineage. Understanding Pst temperature aptitude among geographically distant isolates of the same clonal lineage may help to identify the geographic range of pathogens and also to improve forecast models or breeding programmes. [ABSTRACT FROM AUTHOR]

Wheat streak mosaic tritimovirus (WSMV) seriously damages wheat worldwide. We report analyses of new complete ORF (CO) sequences from seven Australian isolates with 56 COs and 128 coat protein (CP) genes sequenced previously. Eleven CO and three CP sequences were recombinants so were removed from our analyses. Patristic distances of maximum‐likelihood phylogenies of nonrecombinant (n‐rec) CO sequences and their CP sequences were closely correlated (R = 0.994, p ≤ 0.00001). The phylogeny of all 188 n‐rec CP genes had four well‐supported phylogroups (I–IV): phylogroup I (one Mexican sequence), phylogroup II (six Iranian sequences), phylogroup III (48 sequences) and phylogroup IV (133 sequences), each with basal Iranian sequences and either mostly European (phylogroup III) or mostly American (phylogroup IV) terminal sequences. Australian and South American sequences formed a phylogroup IV subcluster within a Pacific Northwest USA cluster. Unlike the Iranian, South American and European populations, the North American and Australian populations demonstrated recent population imbalance. Sample collection dates of 40 CO sequences are known, allowing WSMV phylogeny dating by RTDT methodology. The most recent WSMV ancestor was dated at 1456 CE, and the Australian cluster at 1998.7 CE, only 2–3 years before WSMV was first reported. Tritimoviruses originated in central Eurasia, WSMV first entering wheat in its Middle East domestication centre and one basal lineage being taken to Mexico after the Spanish conquest, whereas the other most basal lineage spread throughout Iran, before spreading to other world regions. Probable future spread to other world regions of additional WSMV phylogroups, and of interphylogroup recombinants, constitutes a biosecurity concern. [ABSTRACT FROM AUTHOR]

Clubroot, caused by Plasmodiophora brassicae, dramatically reduces yields of brassica crops, and once present in a field, can persist in the soil for many years via long‐lived resting spores. Some nonhost crops can stimulate the germination of resting spores, which reduces clubroot inoculum because the pathogen cannot complete its life cycle in the absence of a living host. The effect of selected grasses and other field crops on the concentrations of spores in soil was assessed in two replicated and repeated short‐duration (8‐week) studies under controlled conditions. The spore concentration declined precipitously in the bare soil control relative to the initial spore concentration over the course of both studies. Cultivars of meadow bromegrass, smooth bromegrass and one cultivar of perennial ryegrass reduced the spore concentration compared to the bare soil control in both repetitions of one study, while two cultivars of perennial ryegrass did not reduce the spore concentration. In a second study, spring wheat, perennial ryegrass, barley and field pea reduced spores compared to the bare soil control, but soybean did not. Our hypothesis that larger root systems would produce larger reductions in spore numbers was not supported; there was no correlation between root weight and reduction in spore concentration. We conclude that perennial grasses, spring cereals and field pea can contribute to the reduction of clubroot spores in soil. The advantage of grass crops over annual crops for clubroot management is that movement of infested soil is minimized over the entire duration of the grass stand. [ABSTRACT FROM AUTHOR]

This study follows on from a previous study showing that binary mixtures of wheat cultivars affect the evolution of Zymoseptoria tritici populations within a field epidemic from the beginning (t1) to the end (t2) of a growing season. Here, we focused on the impact of interseason sexual reproduction on this evolution. We studied mixtures of susceptible and resistant cultivars (carrying Stb16q, a recently broken‐down resistance gene) in proportions of 0.25, 0.5 and 0.75, and their pure stands. We determined the virulence status of 1440 ascospore‐derived strains collected from each cultivar residue by phenotyping on seedlings. Virulence frequencies in the ascospore‐derived population were lower in mixtures than in pure stands of the resistant cultivar, especially in the susceptible cultivar residues, as at t2, revealing that the impact of mixtures persisted until the next epidemic season (t3). Surprisingly, after sexual reproduction the avirulence frequencies on the resistant cultivar residues increased in mixtures where the proportion of the susceptible cultivar was higher. Our findings highlight two epidemiological processes: selection within the pathogen population between t1 and t2 driven by asexual cross‐contamination between cultivars (previous study) and sexual crosses between avirulent and virulent strains between t2 and t3 driven by changes in the probabilities of physical encounters (this study). Mixtures therefore appear to be a promising strategy for the deployment of qualitative resistances, not only to limit the intensity of Septoria tritici blotch epidemics, but also to reduce the erosion of resistances by managing evolution of the pathogen population at a pluriannual scale. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) is one of the main causes of wheat yield loss in the world. Apart from good agrotechnical practice, disease‐resistant cultivars are required to prevent yield losses. Breeding of such cultivars is time‐consuming and laborious, mainly due to the quantitative character of such resistance, but can be shortened using precise phenotyping. We show that fluorescence parameters, collected in a high‐throughput system, can be used for estimating wheat STB resistance. Using machine learning methods (deep learning network, random forest), we demonstrate that disease resistance based on the percentage of necrotic leaf area can be estimated by alterations in fluorescence parameters 8 days after inoculation, and before disease symptoms become visible. Moreover, we applied a random forest classifier to assess the significance of fluorescence parameters in an informative way (classification accuracy = 64.84%, p value [Accuracy >No information rate] <0.001). Based on this, we observed extensive alterations in parameters of sensitive cultivars, reflecting worse photosynthetic performance. The most highly altered parameters were fluorescence intensity measurements and descriptors of energy flux through photosystem II (PSII) reaction centres towards PSI such as F2, F3 and F4 fluorescence intensities at 0.1, 0.270 and 2 ms; initial to maximal fluorescence ratio (F0/Fm); the time derivative of relative variable fluorescence (dV/dT0); maximum quantum yield of PSII in the dark‐adapted state (Fv/Fm); maximum electron transport flux at PSII (ET0/RC); maximum trapped excitonic energy flux per excited PSII cross section (CS) at time T0 (TR0/CS0); and quantum efficiency of the reduction of end acceptors dR0 [dR0/(1 − dR0)]. [ABSTRACT FROM AUTHOR]

Chickpea (Cicer arietinum) is a major legume crop, with Australia being the second largest producer worldwide. Pratylenchus neglectus is a root‐lesion nematode that invades, feeds and reproduces in roots of pulse and cereal crops. In Australia, chickpea and wheat (Triticum aestivum) are commonly grown in rotation and annual damage by P. neglectus accounts for large economic losses to both crops. Cultivated chickpea has narrow genetic diversity that limits the potential for improvement in resistance breeding. New collections of wild chickpea species, C. reticulatum and C. echinospermum, have substantially increased the previously limited world collection of wild Cicer germplasm and offer potential to widen the genetic diversity of cultivated chickpea through the identification of accessions with good resistance. This research assessed 243 C. reticulatum and 86 C. echinospermum accessions for response to P. neglectus in replicated experiments under controlled glasshouse conditions from 2013 and 2014 collection missions that were received, tested and analysed in two experimental sets. Multi‐experiment analyses showed lower P. neglectus population densities in both sets of wild Cicer accessions tested than Australia's elite breeding cultivar PBA HatTrick at the significance level p < 0.05. Provisional resistance ratings were given to all genotypes tested in both experimental sets, with C. reticulatum accessions CudiB_008B and Kayat_066 rated as resistant in both Set 1 and Set 2. New sources of resistance to P. neglectus observed in this study can be introgressed into commercial chickpea cultivars to improve their resistance to this nematode. [ABSTRACT FROM AUTHOR]

Wheat farmers rely on fungicides to protect fields against several foliar and flowering diseases, including Fusarium head blight (FHB). A range of active ingredients is used in isolation or in dual premixes that include a dimethylation inhibitor (DMI) or a quinone outside inhibitor (QoI) fungicide. Comprehensive information about fungicide resistance in F. graminearum is available for DMIs, while for QoIs the data are scarce. We characterized 225 strains obtained from two states in southern Brazil, Rio Grande do Sul (RS) and Paraná (PR), in relation to their response to two QoIs. The median EC50 (effective concentration leading to 50% inhibition of conidial germination) value for azoxystrobin (n = 25 isolates) was 2.20 μg/ml in the PR population and 4.04 μg/ml in the RS population. For pyraclostrobin (n = 50), the median EC50 was 0.28 μg/ml in the PR population and 0.24 μg/ml in the RS population. Evidence of cross‐resistance could not be detected. Screening using a discriminatory dose (DD) for azoxystrobin in a larger number of isolates from PR (n = 75) and RS (n = 100) states allowed the detection of 50% and 28% sensitive strains, respectively. Using the DD for pyraclostrobin, 33% and 18.8% were classified as less sensitive in the PR and RS isolates, respectively. In RS, the frequency of less‐sensitive isolates increased over time (2007–2011). No point mutation at any of the target spots (F129L, G137R, G143A) was detected. Our results represent an important step towards the establishment of a sensitivity profile for two of the most commonly used QoIs in commercial premixes targeting FHB control. [ABSTRACT FROM AUTHOR]

Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a severe leaf disease in wheat (Triticum aestivum). To elucidate the effect of powdery mildew on cell redox homeostasis in grains, three wheat cultivars with different resistance, Xi'nong 979 (susceptible), Zhengmai 379 (moderately susceptible), and Zhengmai 103 (resistant), were inoculated with Bgt in the field, and the changes in gene transcription and activity of the antioxidant enzymes in developing grains were analysed. The results showed that the gene expression patterns and enzyme activity changes of guaiacol peroxidase (POD), catalase (CAT), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and 1‐Cys peroxiredoxin (1‐Cys Prx) were similar under powdery mildew conditions. They increased significantly at 10–20 days after anthesis (DAA) in susceptible cultivars and at 20–30 DAA in the resistant cultivar. However, they showed a significant decrease in susceptible cultivars at 20–30 DAA. The gene expression and enzyme activity of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) increased continuously during grain development, especially in susceptible cultivars. The results demonstrated that the antioxidant systems were induced under mild powdery mildew conditions, which was conducive to the synchronous regulation of reactive oxygen species (ROS). However, under severe powdery mildew conditions, the antioxidant systems were inhibited and the regulation of ROS was restricted, resulting in the breakdown of cell redox homeostasis. It is speculated that powdery mildew infection can inhibit the activity of some metabolic proteins (transcription factors or enzymes), change the carbon and nitrogen metabolism of grain cells, and further change the quality of wheat grains. [ABSTRACT FROM AUTHOR]

The chromosomal localization, gene structure, transmembrane proteins, and transcriptome of the wheat Shaker family genes were analysed. The expression patterns of wheat Shaker genes under different stresses were investigated using reverse transcription quantitative PCR (RT‐qPCR). The effect of potassium ion treatment on wheat disease severity caused by powdery mildew was evaluated. To further investigate whether wheat Shaker genes also have inhibitory effects on other pathogens, Nicotiana benthamiana transiently overexpressing Shaker genes was inoculated with Phytophthora infestans and the effects on P. infestans infection judged by leaf lesion diameter. A total of 25 Shaker genes were identified in wheat (TaShaker genes) and were classified into four groups based on phylogenetic analysis. Chromosome mapping results indicated that the 25 TaShaker genes were distributed on 14 chromosomes in wheat (2B, 4A, 4B, 4D, 5A, 5B, and 5D). Gene structure analysis revealed the untranslated region structures were missing in some TaShaker genes, with the number of introns ranging from 7 to 11. Protein transmembrane prediction analysis indicated that there were multiple TaShaker transmembrane proteins. The results of the RT‐qPCR analysis indicated that TaShaker genes were not only involved in regulating drought stress, but could also resist infection by Fusarium graminearum and powdery mildew. This study also found that spraying potassium ion solutions at the seedling stage could reduce the severity of powdery mildew infection in wheat. Moreover, transient overexpression of TaShaker5.1‐3A in N. benthamiana leaves could inhibit P. infestans infection. [ABSTRACT FROM AUTHOR]

Isothiocyanates are biotoxic degradation products formed as a result of enzymatic hydrolysis of glucosinolates present in Brassica species. The application of biofumigant Brassica crops, as an alternative crop protection method for soilborne pathogens and pests is increasingly gaining interest. However, little is known of the potential of biofumigation to reduce the inoculum of Fusarium species affecting cereals. The aim of this study was to evaluate the antifungal activity of five isothiocyanates, namely allyl, benzyl, ethyl, 2‐phenylethyl and methyl isothiocyanates, against germination and growth of Fusarium graminearum under in vitro conditions. Aromatic isothiocyanates were more inhibitory than the aliphatic isothiocyanates against mycelial growth, whereas the reverse was observed for conidial germination. Among the tested isothiocyanates, allyl and methyl isothiocyanates were more efficient overall, showing lower ED50 values (35–150 mg/L) for conidial germination and mycelial radial growth. The findings suggest that Brassica plants containing allyl and methyl glucosinolates could have a suppressive effect, reducing the inoculum of F. graminearum in soil prior to cereal production. [ABSTRACT FROM AUTHOR]

Members of the Fusarium graminearum species complex are known to cause head blight of wheat. A natural nonpathogenic mutant, strain Fa0233007, was found in the strain collection of the Japanese F. graminearum species complex. In addition, this strain cannot form perithecia. Complete linkage of these deficiencies in the progenies obtained from crossing a wild‐type strain and the mutant strain suggested that a single genomic locus was responsible for deficiencies in both traits. The locus was mapped to chromosome 1 using sequence‐tagged markers. An NADPH oxidase gene (NoxA, FGSG00739) was identified in the mapped region, and a 2‐bp deletion that results in premature termination of the open reading frame was detected in the gene. Both pathogenicity and perithecium formation were recovered by FGSG00739 complementation in the mutant strain. [ABSTRACT FROM AUTHOR]

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re‐emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust‐diseased wheat stand. Process‐based agrophysiological models that include disease‐induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered. [ABSTRACT FROM AUTHOR]

The virulence of 57 Australian isolates of Pyrenophora tritici‐repentis (Ptr), a necrotrophic fungal pathogen responsible for the major wheat disease tan spot, was assessed through plant infection assays. Isolates collected from the northern, southern, and western wheat‐cropping regions of Australia were evaluated against 16 Australian bread wheat cultivars under controlled growth conditions. Following infection, the wheat panel displayed varying disease symptoms ranging from tiny necrotic specks to spreading chlorotic and necrotic lesions. Analysis of variance indicated that the wheat cultivar exhibited a greater effect on the disease response, explaining 62.7% of the variation, in comparison to the isolate (10.4%). The interaction between the cultivar and the isolate was statistically significant and was attributed to 9.8% of the total variation. All Ptr isolates examined were able to cause disease, but did not display a clear distinction in virulence on the wheat panel investigated, instead showing subtle differences in aggressiveness. Based on the disease responses, there was no obvious pattern between isolate aggressiveness and cropping region. Some cultivars, such as Hydra, exhibited an effective level of resistance in relation to the panel of isolates tested. All 57 Ptr isolates were found to possess the ToxA effector gene and lack the ToxB effector gene. The gene expression level of ToxA was up‐regulated at 3 days postinfection in both ToxA‐sensitive and ‐insensitive cultivars, independent of ToxA–Tsn1 recognition. [ABSTRACT FROM AUTHOR]

Wheat blast is one of the most important and devastating fungal diseases of wheat in South America, South‐east Asia, and now in southern Africa. The disease can reduce grain yield by up to 70% and is best controlled using integrated disease management strategies. The difficulty in disease management is compounded by the lack of durable host resistance and the ineffectiveness of fungicide sprays. New succinate dehydrogenase inhibitor (SDHI) fungicides were recently introduced for the management of wheat diseases. Brazilian field populations of the wheat blast pathogen Pyricularia oryzae Triticum lineage (PoTl) sampled from different geographical regions in 2012 and 2018 were shown to be resistant to both QoI (strobilurin) and DMI (azole) fungicides. The main objective of the current study was to determine the SDHI baseline sensitivity in these populations. Moderate levels of SDHI resistance were detected in five out of the six field populations sampled in 2012 and in most of the strains isolated in 2018. No association was found between target site mutations in the sdhB, sdhC, and sdhD genes and the levels of SDHI resistance, indicating that a pre‐existing resistance mechanism not associated with target site mutations is probably present in Brazilian wheat blast populations. [ABSTRACT FROM AUTHOR]

Cultivar mixtures slow polycyclic epidemics but may also affect the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken‐down Stb16q gene) over two annual field epidemics. We combined analyses of population "size" based on disease severity, and of population "composition" based on changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. Disease reductions were observed in mixtures late in the epidemic, at the whole‐canopy scale and on both cultivars, suggesting the existence of a reciprocal protective effect. The three cultivar proportions in the mixtures (0.25, 0.5, and 0.75) modulated the decrease in (a) the size of the pathogen population relative to the two pure stands, (b) the size of the virulent subpopulation, and (c) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We argue potential trade‐offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives "efficacy" and "durability," and between the "size" and "frequency" of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission. [ABSTRACT FROM AUTHOR]

The global COVID pandemic has impacted the world in ways and at a scale that few could have predicted, with many industries severely disrupted. Despite this, crops were sown and harvested, food was produced and agriculture continued to function, albeit it with many logistical challenges. Plant health lies at the heart of preventing crop losses through a combination of varietal resistance and agronomic practices. In the case of foliar plant diseases in wheat, varietal resistance plays a key role, but the use of synthetic fungicides is essential to minimize crop losses. European arable production faces a dilemma: how to contribute and maintain global food supplies but at the same time decrease emissions of greenhouse gases (GHGs), reduce inputs potentially harmful to biodiversity, society and the environment while ensuring no more land is brought into production. Throughout history, major disruptions in society have led to big steps in agricultural innovation. Presently, the major disruptive forces in Europe are not just a result of the COVID pandemic but the increasingly urgent need to address climate change. Within the European Green Deal, the Farm‐to‐Fork strategy is in place to help achieve climate neutrality by 2050, aiming for a reduction of GHG emissions of 55% by 2030. To achieve this, there will need to be a major adjustment to how food is produced, a realignment in plant health strategies and accelerated innovation across the agricultural sector. This paper aims to evaluate how synthetic fungicides presently contribute to plant health (mainly wheat) and food production as well as the management of GHG emissions. In addition, it explores the future challenges and prospects for their positive contribution in achieving global food security alongside emerging innovative technologies. [ABSTRACT FROM AUTHOR]

Tan spot, caused by the fungus Pyrenophora tritici‐repentis (Ptr), is a disease that has become more prevalent and intense in wheat crops in Argentina in recent years. Failure to control the disease with strobilurin fungicides, which were once effective, has been observed in different zones where wheat is grown. However, whether or not true resistance is present in the pathogen population in the region is not scientifically confirmed. This study evaluated the sensitivity of numerous Ptr isolates to representative QoI fungicides used in Argentina through in vitro and in planta assays, as well as through molecular analysis. Eighty‐two monosporic isolates obtained in different locations in the north and south of Buenos Aires province in 2014, 2016, and 2018 were tested to determine sensitivity to selected QoI fungicides in conidial germination and mycelial inhibition assays, as well as in molecular analysis. Conidial germination was not inhibited at 1 µg/ml of azoxystrobin, trifloxystrobin, and pyraclostrobin. On the other hand, mycelial growth was inhibited by 59%, 56%, and 86% at 100 µg/ml of azoxystrobin, trifloxystrobin, and pyraclostrobin, respectively. The molecular analysis detected the G143A mutation in the cytb gene of all the 82 Ptr isolates, but the F129L and G137R substitutions were not present. This study documents the G143A mutation conferring QoI resistance in Ptr in South America. The findings of this study are key for future decisions regarding use of fungicide and rotation in the region. [ABSTRACT FROM AUTHOR]

Karnal bunt, a disease of wheat, durum, rye, and triticale, is subject to strict quarantine restrictions worldwide. The disease is considered a major threat to food security, due to its use as a non‐tariff trade barrier by several wheat‐importing countries. In this paper, we analysed seven years of phenotypic data to search for quantitative trait loci (QTLs) associated with resistance in common wheat, validated the QTLs using an independent population, and assessed the potential of genomic selection as a tool for pre‐emptive breeding. The QTL study used phenotypic data collected from artificially inoculated field experiments involving two historical Karnal bunt resistance populations: WH542 × HD29 and WH542 × W485. QTL analyses detected four significant (p < 0.001) QTLs on chromosomes 1A, 3A, 4B, and 6B, which explained between 13.7% and 15.7% of the phenotypic variation. A panel of 130 cultivars was used to validate QTL effects. These were genotyped with the same DArTseq protocol, and two of the four QTLs were significantly (p < 0.001) associated with Karnal bunt resistance in the validation panel. The potential of genomic selection was investigated by comparing accuracies of a model trained with all available markers and a model based solely on validated QTL information from the biparental populations. Genomic prediction accuracy, based on the two scenarios, averaged 0.43 and 0.33, respectively, suggesting that even in situations where phenotyping is difficult due to quarantine restrictions, the prospects for pre‐emptive breeding against Karnal bunt are encouraging, and resources are now available that will reduce the cost burden. [ABSTRACT FROM AUTHOR]

To understand the yield response of cereal cultivars to Pratylenchus thornei, eight experiments were conducted within the subtropical northern, and temperate southern grain‐producing regions of Australia. Wheat cultivars (Triticum aestivum) ranging from susceptible to moderately resistant to P. thornei were grown in Year 1 to establish a range of population densities. In Year 2 before sowing, P. thornei was quantified in each plot and six cereal cultivars were each grown on a similar range of population densities (average minimum to maximum of 3.4–60.6 P. thornei/g soil); P. thornei was quantified again at harvest. In the four experiments in the northern region there was a significant, negative logarithmic response of yield of the three most intolerant/susceptible cultivars as P. thornei population densities increased (yield decreased 172–479 kg/ha per unit increase in loge‐transformed P. thornei/g soil). The responsiveness of yield to increasing P. thornei population densities diminished as the tolerance and resistance of the cultivars improved. In the southern region, there was no relationship between yield and P. thornei in three experiments and minor, positive increases in one experiment (1.6 kg/ha per unit increase in P. thornei/g soil). Across both regions, the change in P. thornei population densities from sowing to harvest was logarithmic and positive, and generally greatest in the northern region. The contrast of responses of cereal cultivars between the regions, despite similar population densities of P. thornei, is indicative of the influence of the environment particularly on tolerance, therefore management with a regional focus is essential. [ABSTRACT FROM AUTHOR]

Non‐crop plants such as grasses and volunteer plants are an inseparable part of the flora of crop fields and can influence virus incidence in crop plants. The presence of grasses as virus reservoirs can lead to a higher probability of virus incidence in crop plants. However, the role of reservoirs as an inoculum source in agricultural fields has not been well studied for many viral diseases of crops. Grasses have been found to constitute potential reservoirs for cereal‐infecting viruses in different parts of the world. This study revealed that cereal‐infecting viruses such as wheat dwarf virus (WDV), barley yellow dwarf viruses (BYDVs), and cereal yellow dwarf virus‐RPV (CYDV‐RPV) can be found among ryegrass growing in or around winter wheat fields. Phylogenetic analysis showed that a WDV isolate from ryegrass was a typical WDV‐E isolate that infects wheat. Similarly, a ryegrass isolate of barley yellow dwarf virus‐PAV (BYDV‐PAV) grouped in a clade together with other BYDV‐PAV isolates. Inoculation experiments under greenhouse conditions confirmed that annual ryegrass of various genotypes can be infected with WDV to a very low titre. Moreover, leafhoppers were able to acquire WDV from infected ryegrass plants, despite the low titre, and transmit the virus to wheat, resulting in symptoms. Information from the grass reservoir may contribute to improving strategies for controlling plant virus outbreaks in the field. Knowledge of the likely levels of virus in potential reservoir plants can be used to inform decisions on insect vector control strategies and may help to prevent virus disease outbreaks in the future. [ABSTRACT FROM AUTHOR]

Wheat blast caused by Magnaporthe oryzae pathotype Triticum (MoT), initially restricted to South America, is a global threat for wheat after spreading to Asia in 2016 by the introduction of contaminated seeds, raising the question about transmission of the pathogen from seeds to seedlings, a process so far not well understood. We therefore studied the relationship between seed infection and disease symptoms on seedlings and adult plants. To accomplish this objective, we inoculated spikes of wheat cv. Apogee with a transgenic isolate (MoT‐DsRed, with the addition of being resistant to hygromycin). We identified MoT‐DsRed in experiments using hygromycin resistance for selection or by observation of DsRed fluorescence. The seeds from infected plants looked either apparently healthy or shrivelled. To evaluate the transmission, two experimental designs were chosen (blotter test and greenhouse) and MoT‐DsRed was recovered from both. This revealed that MoT is able to colonize wheat seedlings from infected seeds under the ground. The favourable conditions of temperature and humidity allowed a high recovery rate of MoT from wheat shoots when grown in artificial media. Around 42 days after germination of infected seeds, MoT‐DsRed could not be reisolated, indicating that fungal progression, at this time point, did not proceed systemically/endophytically. We hypothesize that spike infection might occur via spore dispersal from infected leaves rather than within the plant. Because MoT‐DsRed was not only successfully reisolated from seed coats and germinating seeds with symptoms, but also from apparently healthy seeds, urgent attention is needed to minimize the risks of inadvertent dispersal of inoculum. [ABSTRACT FROM AUTHOR]

This study provides new insights into the role of photoprotection in preformed and induced defence of two wheat genotypes with contrasting phenotypes to infection by Zymoseptoriatritici. We investigated the mechanisms of the photoprotective response during early infection, including nonphotochemical quenching (NPQ), β‐carotene‐derived xanthophylls, reactive oxygen species, and the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Furthermore, we quantified the effects of pathogenesis on photosynthesis, stomatal control, and expression of plant defence molecular markers. The photoprotective mechanism of successful defence involved the qI component of NPQ leading to rapid down‐regulation of photosystem II quantum yield and chlorophyll a:b, increased biosynthesis of the xanthophyll neoxanthin and ABA, and the expression of chloroplast‐specific enzymes to engage in scavenging of O2●−. Elevated ABA in the resistant genotype correlated with preformed leaf defence traits including low stomatal density, increased expression of wax biosynthesis, and lignification. Z. tritici exhibited reduced germination and branching on the resistant host genotype and hijacked stomatal control in both genotypes by enhancing stomatal sensitivity to light. Increased biosynthesis of JA and anthocyanins, in contrast to SA, were quantified in the incompatible interaction. Our results indicate that ABA and JA in antagonistic action to SA were associated with defence in the resistant genotype, Cougar, against Z. tritici. [ABSTRACT FROM AUTHOR]

Stem rust caused by Puccinia graminis f. sp. tritici is one of the most devastating diseases of wheat. Breakdown of host resistance under field conditions triggered by the evolution of new pathogenic races and pathotypes is a perennial threat for wheat cultivation. Rice, often grown in a rice–wheat cropping system, is immune to rust infection. Our microscopic studies revealed that P. graminis f. sp. tritici, although displaying nearly identical uredospore germination, stomatal entry, and epi‐ and endophytic mycelial growth in rice and wheat, failed to sporulate to cause rust disease in rice. We identified 18 key defence signalling genes in rice and unravelled their elicitation dynamics in time‐course studies during infection. ICS1, NPR1‐3, PRs, EDS1, PAD4, FMO1 (salicylic acid [SA] signalling), and ethylene‐related genes (ACO4 and ACS6) were strongly elicited in rice. However, genes from the jasmonic acid (JA) signalling pathway (LOX2, AOS2, MYC2, PDF2.2, JAZ8, JAZ10) showed a delayed response during colonization in rice compared to an early or no induction in wheat. However, the JA/ethylene marker gene PDF2.2 was strongly induced in wheat as early as 12 hr postinoculation. Furthermore, rice and wheat displayed specific profiles of accumulation of various phenolic acids during P. graminis f. sp. tritici 40A infection. We propose a model where a differential modulation of the SA/JA‐dependent defence network may modulate nonhost resistance. A deeper understanding of the molecular mechanism governing differential elicitation of defence signalling may provide a novel resistance mechanism for the sustainable management of rust diseases. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is currently the main threat to worldwide wheat production in temperate climates. Understanding the genetic mechanisms that underpin the Z. tritici–wheat interaction will be crucial for generating new control strategies against STB. Plant hormones are essential regulators of growth and immunity. In particular, jasmonic acid (JA) plays a central role in defence against necrotrophic plant pathogens, but its role in mediating immunity against Z. tritici is largely unknown. Here we identify the transcription factor TaWRKY10 that is taxonomically restricted to the grass subfamily Pooideae as a novel regulator of JA responses in wheat. We demonstrate by using virus‐induced gene silencing that silencing TaWRKY10 leads to increased resistance against Z. tritici with an earlier onset of necrotic symptoms, but with reduced pathogen sporulation. Wheat plants silenced for TaWRKY10 show an up‐regulated JA response. Transcriptional profiling of TaWRKY10 knock‐down plants indicates that it is a negative regulator of the JA receptor TaCOI1 gene expression. Our data indicate that TaWRKY10 down‐regulates JA responses, contributing to the susceptibility of wheat to Z. tritici. We postulate that manipulating TaWRKY10 may provide a strategy to boost STB resistance in wheat. [ABSTRACT FROM AUTHOR]

Globally, bread wheat production is threatened by fungal diseases, including the devastating disease Septoria tritici blotch (STB). Given the global importance of STB, and the difficulty in identifying novel sources of resistance to this disease, we screened a variety of wheat genotypes, including wild, ancestral, and mutagenized lines, for their STB response. This delineated a panel of wild wheat relatives and Watkins collection lines with exceptional resistance to a range of Zymoseptoria tritici isolates, some of which are highly virulent on modern, elite wheat varieties. Additionally, we characterized the STB susceptibility of 500 lines of the wheat cultivar Cadenza TILLING population and developed backcross derivatives of two TILLING lines that show dominant partial resistance to STB. These backcross lines are partially resistant to multiple isolates of Z. tritici, and, with the wild and ancestral lines identified, provide a useful reservoir of STB‐resistant germplasm for use in wheat breeding programmes. [ABSTRACT FROM AUTHOR]