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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]

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]

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]

Cultivar disease resistance ratings to nodorum blotch (caused by Parastagonospora nodorum) provide critical information to growers to assist with disease management. However, less has been done in terms of yield losses from diseases under different cultivar resistance scenarios. The purpose of this study was to characterize yield and quality loss responses to wheat nodorum blotch as influenced by variety partial resistance, epidemic intensity, and environment. The trial series includes four site/years in Western Australia. Five varieties, Magenta, Calingiri, Trojan, Janz, and Scout were used for all four trials. These varieties represented resistant/susceptible categories MRMS, MS, MSS, S, and SVS, respectively, and were selected on the basis that they were adapted to the western region, had similar maturities, and were resistant to diseases that were potential contaminants. Trials were sown in a strip‐plot design with three replicates and five disease levels, with intersecting main‐plots of varieties and disease levels, which facilitated comparisons across disease levels within varieties. Current categories of resistance were well reflected in yield and quality responses. A negative exponential relationship was observed between yield and disease, with a nonlinear yield loss function for both flag leaf and glume infection. This indicates that yield is most affected during early stages of disease on flag leaves and glumes. The functional form of yield loss response over four site years was similar among varieties, but varieties differed in their extent of disease expression. Partial resistance in commercial wheat varieties reduced yield loss by 40%–60% of losses observed in susceptible varieties. [ABSTRACT FROM AUTHOR]

Canada is one of the largest wheat producers in the world, and wheat is grown over an area spanning most of the southern latitudes, with the prairie region (provinces of Saskatchewan, Alberta, and Manitoba) being the main producer. Several pathogens and pests attack wheat, but at present fusarium head blight (FHB), stripe rust, and leaf spots are the most damaging diseases to wheat production in Canada. Historically, smuts, stem rust, and leaf rust caused major crop losses in Canada and can still pose serious threat if management practices are relaxed. Cropping practices used by Canadian farmers to grow and harvest wheat over the last century have influenced disease development and pathogen biology, affecting the severity, incidence, and prevalence of crop diseases over time. Changes such as reduced tillage coincide with emergence of residue‐borne diseases, such as FHB and leaf spots, while the deployment of resistant cultivars and increased fungicide use has resulted in the reduction of common bunt, stem, and leaf rust. This review will discuss the influence of long‐term cropping practices, alone or in combination, on the biology, emergence, and prevalence of wheat diseases in Canada over the last century. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) of wheat is a destructive fungal disease worldwide and has become more severe over the last two decades. Development of FHB resistant wheat varieties is the most effective way to manage FHB. The middle and lower reaches of the Yangtze River are the traditional FHB epidemic areas in China. The landraces and germplasms with resistance to FHB originating from this region were used to identity FHB resistance quantitative trait loci (QTLs). Yangmai 158 and Ningmai 9 are the most popular varieties for commercial wheat production in this region and both have moderate FHB resistance. A high‐density genetic map was constructed using 282 recombinant inbred lines (RILs) from a cross between Ningmai 9 and Yangmai 158. Ten QTLs related to Type II FHB resistance were identified, and QFhb‐3B.1 and QFhb‐5A were stably detected across all environments. Based on position alignment, QFhb‐3B.1 from Ningmai 9 is likely to be Fhb1 and QFhb‐5A from Yangmai 158 is a novel QTL not previously described. A competitive allele‐specific PCR (KASP) marker closely linked to QFhb‐5A was developed and could be used for marker‐assisted selection. Distribution of QFhb‐5A was tested with numerous accessions from a widespread core collection. The results suggest that QFhb‐5A has undergone both natural and artificial selection. Some RILs with both Fhb1 and QFhb‐5A presented better FHB resistance than the parents and could be used in FHB resistance breeding. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) disease of wheat is caused by the fungal pathogen Zymoseptoria tritici. It is the most important foliar disease of wheat in western Europe and affects wheat cultivation worldwide. The combination of intensive fungicide usage, a polycyclic asexual life cycle and an active sexual cycle has led to the emergence of fungal strains resistant/tolerant to all the major classes of fungicides used in its control. The hallmark of this disease is a long, symptomless latent phase that precedes the onset of visible symptoms. Understanding the processes that occur during the symptomless phase of infection is paramount in developing alternative strategies for disease control; however, large gaps in our knowledge of the disease remain. The known unknowns of the latent stage of infection can be summarized in three questions. Does the fungus initiate or manipulate host defences to trigger programmed cell death in order to facilitate nutrient acquisition or is the host acting exclusively? Does the fungus feed during both the latent phase and the necrotrophic phase like a true hemibiotroph? Does the long latent phase serve a beneficial function for the fungus or is it simply an artefact of evolution? This review aims to distil observations made during studies that have directly or indirectly contributed to answering these questions and points towards their most likely answers. [ABSTRACT FROM AUTHOR]

Known and unknown genes conferring seedling and adult plant resistance (APR) to leaf rust, stem rust and stripe rust were detected either singly or in combination in a set of 136 African wheat genotypes using multi‐pathotype tests with characterized Australian Puccinia triticina (Pt), P. graminis f. sp. tritici (Pgt) and P. striiformis f. sp. tritici (Pst) pathotypes. Lines Beladi 132, IYN 68/9.44, Kenya Kifaru and Kenya Mbweha were postulated to carry resistance against multiple pathotypes of Pt, Pgt and Pst, whereas IAR/W/163‐3, Grano Di Moggio Tipo 44 and Trigo 48 had resistance against all pathotypes tested in the current study. Field evaluation with the three rust pathogens detected low to high APR in more than 50% of lines, and while most tested positive with markers linked to known APR genes (csLV34, csLV46G22, TM10KASPAR, csGS, Cfb5006 and csSr2), many carried unidentified and useful resistance to all three rusts. Genetic analysis of F3 mapping populations based on seven genotypes showed either monogenic or digenic inheritance of APR to leaf rust, stem rust and stripe rust. The lines postulated to carry effective uncharacterized seedling genes and APR genes are of great potential value in diversifying resistance to help achieve durable control of all three rust diseases of wheat. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB), caused by fungi belonging to the Fusarium genus, is a widespread disease of wheat (Triticum aestivum) and other small‐grain cereal crops. The main causal agent of FHB, Fusarium graminearum, produces mycotoxins mainly belonging to type B trichothecenes, such as deoxynivalenol (DON), that can negatively affect humans, animals and plants. DON detoxification, mainly through glucosylation into DON‐3‐O‐glucose, has been correlated with resistance to FHB. A UDP‐glucosyltransferase from the model cereal species Brachypodium distachyon has been shown to confer resistance both to initial infection and to spike colonization (type I and type II resistances, respectively). Here, the functional characterization of transgenic wheat lines expressing the Bradi5g03300 UGT gene are described. The results show that, following inoculation with the fungal pathogen, these lines exhibit a high level of type II resistance and a strong reduction of mycotoxin content. In contrast, type I resistance was only weakly observed, although previously seen in B. distachyon, suggesting the involvement of additional host‐specific characteristics in type I resistance. This study contributes to the understanding of the functional relationship between DON glucosylation and FHB resistance in wheat. [ABSTRACT FROM AUTHOR]

Two field experiments (Exp. 1 and Exp. 2) were carried out to assess the physiological performance and grain yield of wheat cultivars BR-18 (moderately resistant) and Guamirim (susceptible) inoculated with Pyricularia oryzae in plots treated or untreated with Ópera (fungicide 13.3% epoxiconazole + 5% pyraclostrobin). Results from regression analyses indicated that spike and leaf blast severity at 10-14 days after inoculation (dai) were associated with greater yield losses (highest negative slope) than severity at 18-22 dai. Relative to untreated Guamirim, there were 0.3% and 16% increases in Exp. 1 and 2, respectively, for untreated BR-18 (resistance alone). For fungicide treatment alone, the mean yield of Guamirim increased by 20% and 61% in Exp. 1 and 2, respectively, relative to the untreated fungicide control, whereas for the fungicide treated BR-18, the mean yield increased by 26% and 83% in Exp. 1 and 2, respectively. Fungicide application and cultivar resistance resulted in higher measures of leaf health and photosynthetic performance in both spikes and leaves than in the untreated susceptible reference treatment. The results from this study may be useful in future efforts to develop crop loss models and management guidelines for wheat blast. [ABSTRACT FROM AUTHOR]

Zymoseptoria tritici, the causal agent of septoria tritici blotch, a serious foliar disease of wheat, is a necrotrophic pathogen that undergoes a long latent period. Emergence of insensitivity to fungicides, and pesticide reduction policies, mean there is a pressing need to understand septoria and control it through greater varietal resistance. Stb6 and Stb15, the most common qualitative resistance genes in modern wheat cultivars, determine specific resistance to avirulent fungal genotypes following a gene-for-gene relationship. This study investigated compatible and incompatible interactions of wheat with Z. tritici using eight combinations of cultivars and isolates, with the aim of identifying molecular responses that could be used as markers for disease resistance during the early, symptomless phase of colonization. The accumulation of Ta MPK3 was estimated using western blotting, and the expression of genes implicated in gene-for-gene interactions of plants with a wide range of other pathogens was measured by qRT- PCR during the presymptomatic stages of infection. Production of Ta MPK3 and expression of most of the genes responded to inoculation with Z. tritici but varied considerably between experimental replicates. However, there was no significant difference between compatible and incompatible interactions in any of the responses tested. These results demonstrate that the molecular biology of the gene-for-gene interaction between wheat and Zymoseptoria is unlike that in many other plant diseases, indicate that environmental conditions may strongly influence early responses of wheat to infection by Z. tritici, and emphasize the importance of including both compatible and incompatible interactions when investigating the biology of this complex pathosystem. [ABSTRACT FROM AUTHOR]

The use of cultivar mixtures to control foliar fungal diseases is well documented for windborne diseases, but remains controversial for splash-dispersed diseases. To try to improve this strategy, a cultivar mixture was designed consisting of two wheat cultivars with contrasted resistance to Mycosphaerella graminicola, responsible for the rainborne disease septoria tritici blotch ( STB), in a 1:3 susceptible:resistant ratio rather than the 1:1 ratio commonly used in previous studies. The impact of natural STB epidemics in this cultivar mixture was studied in field experiments over 4 years. Weekly assessments of the number of sporulating lesions, pycnidial leaf area and green leaf area were carried out on the susceptible cultivar. In years with sufficient STB pressure, disease impacts on the susceptible cultivar in the mixture were always significantly lower than in the pure stand (e.g. 42% reduction of pycnidial leaf area for the three upper leaves in 2008 and 41% in 2009). In years with low STB pressure (2010 and 2011), a reduction of disease impacts was also shown but was not always significant. After major rainfall events, the number of sporulating lesions observed on the susceptible cultivar after one latent period was reduced on average by 45% in the mixture compared to the pure stand. All the measurements showed that a susceptible cultivar was consistently protected, at least moderately, in a mixture under low to moderate STB pressure. Therefore, the results prove that the design of an efficient cultivar mixture can include the control of STB, among other foliar diseases. [ABSTRACT FROM AUTHOR]

Wheat stem rust samples were collected in 2006 and 2007 in the Arsi, Bale, Shewa and northwest regions of Ethiopia to determine virulence diversity and race distribution in Puccinia graminis f.sp. tritici populations. Stem rust incidence was high in Arsi, Bale and east Shewa. In northwest Ethiopia, and north and west Shewa, stem rust was prevalent at low levels. A total of 152 isolates was analysed and 22 races were identified. Races TTKSR (Ug99), TTHSR and RRTTR were predominant, with frequencies of 26·6, 17·7 and 11·1%, respectively. These races were also detected in all regions. The highly virulent race designated Ug99 was present throughout the country and dominated in all regions except northwest Ethiopia. A variant of Ug99 virulent against the stem rust resistance gene Sr24 was not detected in this study. Four stem rust resistance genes ( Sr13, Sr30, Sr36 and SrTmp) were found to confer resistance to most of the races prevalent in Ethiopia. With the exception of Sr30, which is not effective against Ug99, these genes could be used in breeding for resistance to stem rust in Ethiopia. [ABSTRACT FROM AUTHOR]

A lesion-mimic mutant was obtained from a mutagenic treatment performed with ethyl methanesulfonate on the Argentine bread wheat ( Triticum aestivum) cultivar Sinvalocho M.A. The HLP (hypersensitive-like phenotype) mutant exhibited tiny, discrete, white lesions in the absence of any pathogen, resembling the typical hypersensitive response (HR). The lesions only became evident once the fifth or sixth leaf emerged, and spread at random along the leaf blades and leaf sheaths of the developing plant, including tissues of the spike. Because the lesion-mimic mutant showed no lesions at the seedling stage, the phenotypes of both the mutant and its mother line were identical at this point. Histochemical studies showed that spontaneous hypersensitive-like lesions in the HLP mutant corresponded to cell death. In leaf-rust ( Puccinia triticina) infection experiments performed at seedling and adult-plant stages, adult HLP plants showed enhanced resistance to leaf-rust attack compared with plants of Sinvalocho M.A. of comparable developmental stage, suggesting that the HLP mutation may confer increased resistance to the fungus. Because enhanced resistance coincided with the presence of spontaneous HR lesions, activation of HLP plant defence responses appeared to be tightly linked to this phenomenon. Final plant height and yield components in the lesion-mimic mutant did not differ from those of the mother line, indicating that the HLP mutation caused no detrimental pleiotropic effects that significantly affected agronomic performance. These data support the direct use of mutations in disease-resistance breeding. [ABSTRACT FROM AUTHOR]

Septoria tritici blotch (STB) is a major disease of wheat, reaching epidemic proportions in many parts of the world. In several studies, taller, later-maturing cultivars have had lower disease levels. This study was undertaken to investigate the genetic associations of natural field infection by STB with disease-escape mechanisms related to heading date and height components, mainly leaf spacing, in a population where height and maturity are not controlled by major genes. In field trials of a single seed-descent population of a cross between two nonsemi-dwarf cultivars, Apollo (with strong partial resistance to STB) and Thésée (susceptible), conducted over 3 years, there was a negative correlation between STB and heading date. There was no correlation between STB and distance from stem base to leaf 2; and there was an unexpected positive correlation between STB and distance from flag leaf to leaf 2, which contradicted the so-called ‘ladder effect’ postulated in STB epidemiology. No effect was detected of the presence of the 1BL−1RS translocation on STB levels. The largest single contributor to variation in STB levels was genetic variation between the progeny lines, and the narrow-sense heritability was 42%. These results suggest that breeders can select for STB resistance alongside optimal stature within the range of height which is adaptive in a particular environment. [ABSTRACT FROM AUTHOR]

Several wheat genotypes, including eight with known field responses, were evaluated for their reaction to Soil-borne cereal mosaic virus (SBCMV, genus Furovirus) by growing in naturally infested soil under controlled environment conditions. Virus antigen titres in the foliage 8–9 weeks after sowing mostly reflected the field responses, showing that growth chamber-based tests can be used to improve the speed and reliability of germplasm screening. Such tests were used to determine the mode of inheritance of the SBCMV resistance in cv. Cadenza, commonly used in UK wheat-breeding programmes. One hundred and eleven doubled haploid (DH) lines derived from an F1 of a cross between cvs Cadenza (resistant) and Avalon (susceptible) were evaluated. This DH population segregated for the reaction to SBCMV in a ratio of 1 : 1 (resistant : susceptible). This suggests that the SBCMV resistance is controlled by a single gene locus. As a first step towards identification of new sources of improved SBCMV resistance (e.g. immunity) as well as sources of the resistance to the virus vector, Polymyxa graminis, a set of 26 Triticum monococcum lines of diverse geographical origin was also screened. Most lines were susceptible to SBCMV, but one line of Bulgarian origin was resistant to the virus and possibly partially resistant to the virus vector. [ABSTRACT FROM AUTHOR]

Data from field experiments were used to test whether disease observations on lower leaves of wheat were good predictors of future epidemic development in the upper canopy. Fungicide treatments to replicated plots in 1994 and 1995 caused variation in levels of initial inoculum of urediniospores of yellow rust (Puccinia striiformis ). Observations of symptom severity were made on individual leaf layers throughout the season. Sporulating lesions on lower leaves were considered to be a measure of inoculum source strength for transfer to upper culm leaves. Low source strengths were associated with delays in epidemic development on the upper leaves, as quantified by a location parameter, t m , the time at which severity reached half of the asymptote value in logistic fits to disease progress data on the upper leaves. However, there was much unexplained variation, probably due to extraneous variation in upward transfer efficiency of inoculum and rates of epidemic development. Vanderplank's sanitation ratio theory was used to account for variation in inoculum transfer and epidemic rate. The analysis revealed that if the aim is to predict disease on a newly emerged culm leaf, during the period when it can be treated effectively with fungicide, then observations of disease two leaves further down the culm were of the greatest predictive value (R 2 = 86%). These observations, however, need to be integrated with information about factors affecting upward inoculum transfer and rates of epidemic development if acceptable predictive precision is to be achieved. [ABSTRACT FROM AUTHOR]

The effect of take-all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with 15 N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take-all lesions. The 15 N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm. [ABSTRACT FROM AUTHOR]

More than 20000 wheat plants, derived from callus culture of immature wheat embryos were assessed for reaction to the take-all fungus (Gaeumannomyces graminis var. tritici) using a test-tube assay. Lines with less root and shoot blackening and more remaining green tissue than parental lines were identified in the SC3 generation. However these lines had more root and shoot blackening and less remaining green tissue in subsequent generations. The changes in reaction to the fungus may therefore have been epigenetic. The potential of this tissue culture derived material for breeding take-all resistant wheats is discussed. [ABSTRACT FROM AUTHOR]

Linear models were used to investigates the effects and interactions of treatments for the control of disease in multifactorial experiments on the dynamics of the take-all disease of wheat. Analyses were based on repeated measures of disease on second successive winter wheat crops in three successive seasons. The treatments were date of sowing, presence or absence of triadimenol-containing seed treatment, autumn nitrogen and chloride applications, timing of early spring nitrogen and total spring nitrogen applications. The effects of treatments were investigated on linear and quadratic trends of disease increase and on the integral amount of disease over time. Different disease variables were used to express disease relative to the total and diseased plant populations. The effects of treatments on absolute and relative numbers of diseased roots per plant were also analysed. During three seasons when disease was never severe, the effects of the treatments were shown to be variable. Late sowing consistently reduced disease during the early stages of epidemic (in the winter months). The effect of late sowing in reducing disease, however, persisted through to the end of the growing season in only one of the 3 years of the study. Autumn nitrogen application and Baytan seed treatment (containing triadimenol) also reduced disease in some seasons. The presence of an effect for either was dependent on sowing date and was most evident on the proportion of diseased roots relative to the diseased plant rather than the total plant population. [ABSTRACT FROM AUTHOR]

Aneuploid and intervarietal chromosome substitution lines of wheat cv. Chinese Spring were used to study the effects of homoeologous chromosomes 7A, 7B and 7D upon adult plant resistance to yellow rust (Puccinia striiformis), Chromosomes 7B and 7D carry factors upon their short arms which interact to influence resistance. The results can be explained if there is a single locus determining resistance upon the short arms of chromosomes 7B and 7D. These loci may be homoeo-allelic; however, no evidence was found for a corresponding locus upon the short arm of chromosome 7A. Three homologous variants of the factor 7Ds were found but no variation was found for the factor on 7Bs. [ABSTRACT FROM AUTHOR]