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Puccinia triticina, the causal agent of wheat leaf rust, is a dynamic pathogen causing significant yield losses worldwide. In this study, we analysed the virulence and genetic structure of 98 P. triticina isolates collected in Canada between 2018 and 2020. Isolates from Manitoba and Saskatchewan were found to be highly related for virulence, as were isolates from Quebec and Ontario. Isolates from Alberta had a virulence profile more similar to those from Manitoba and Saskatchewan than to Ontario and Quebec. To study the genetic structure of P. triticina populations, we used the restriction site‐associated DNA (RAD) genotyping‐by‐sequencing method to identify single‐nucleotide polymorphisms (SNPs). The Puccinia DNA sequences were aligned against the reference genome of P. triticina race BBBD and 1898 SNPs were identified. The phylogenetic analysis using SNP markers grouped these P. triticina into three genetic clades. The separation of P. triticina into three genetic clades was also supported by principal component analysis. Isolates from Clade 1 and Clade 2 were found throughout Canada, whereas Clade 3 isolates were only found in Ontario and Quebec. There were differences in virulence profiles among P. triticina isolates from the three genetic clades and a general correlation between virulence phenotypes and SNP genotypes was observed. These results indicate that the SNPs derived from RAD genotyping‐by‐sequencing could be useful in tracking the genetic and virulence dynamics of this pathogen in Canadian wheat. [ABSTRACT FROM AUTHOR]

Eight wheat cultivars, Sakha-94, Giza-171, Sids-1, Sids-12, Sids-13, Shandweel-1, Misr-1, and Misr-2, were evaluated for leaf rust at the seedling and adult stages in the 2021 and 2022 seasons. Biochemical, histological, and genetic analyses were performed to determine the link between cultivars that were either sensitive or resistant to the disease. Misr-2 and Giza-171 cultivars had the highest levels of resistance to leaf rust races in 2021 (LTCGT, STSJT, and TTTST) and 2022 (MBGJT, TTTKS, and TTTTT) at the seedling stage. However, at the adult stage, Sakha-94, Giza-171, Misr-1, and Misr-2 cultivars had the highest levels of resistance; consequently, they had the lowest final disease severity and the lowest values of AUDPC. The correlation between the seedling reaction and adult reaction was non-significant, with values of 0.4401 and 0.4793 in the 2021 and 2022 seasons, respectively. Throughout the biochemical, histological, and genetic analyses, it was observed that catalase, peroxidase, and polyphenol oxidase activities significantly increased in the resistant cultivars. The discoloration of superoxide (O2-) and hydrogen peroxide (H2O2) significantly decreased in resistant and moderately resistant wheat cultivars (Sakha-94, Giza-171, Misr-1, and Misr-2); higher hydrogen peroxide (H2O2) and superoxide (O2-) levels were recorded for the susceptible cultivars compared to the resistant cultivars. Molecular markers proved that the Lr50 gene was detected in the resistant cultivars. Puccinia triticina infections negatively affected most histological characteristics of flag leaves, especially in susceptible cultivars. The thickness of the blade (µ), the thickness of the upper and lower epidermis (UE and LE), the thickness of mesophyll tissue (MT), and bundle length and width in the midrib were decreased in susceptible cultivars such as Sids-1, Sids-13, and Shandwel-1 compared with resistant cultivars. [ABSTRACT FROM AUTHOR]

Wheat leaf rust and stripe rust are important diseases worldwide. Breeding resistant cultivars is an effective means to control wheat leaf and stripe rust. Wheat line L224-3 currently has high resistance to wheat leaf and stripe rust at the field. In this study, 166 recombinant inbred lines (RILs) derived from the L224-3 × Zhengzhou 5389 cross were used to map quantitative trait locus (QTL) for leaf and stripe rust resistance. The RILs and two parents were phenotyped for leaf rust severity at Baoding in Hebei province and Zhoukou in Henan province in the 2015/2016 and 2016/2017 cropping seasons, and for stripe rust severity at Baoding in Hebei Province and Mianyang in Sichuan Province in the 2015/2016 and 2016/2017 growth seasons. All the RILs and parents were also genotyped with the 660 K SNP array and simple sequence repeat (SSR) markers to screen for potential polymorphic markers associated with rust resistance. Four QTLs on chromosomes 1A, 2A, 4B and 7B, were detected using inclusive composite interval mapping (IciMapping). QLr.hbau-1A/QYr.hbau-1A, derived from susceptible parent Zhengzhou 5389, was pleiotropic for both leaf rust and stripe rust resistance and maybe a novel QTL. The second QTL, QLr.hbau-2A/QYr.hbau-2A derived from L224-3 for leaf rust and stripe rust resistance is possibly Lr37/Yr17. QLr.hbau-4B/QYr.hbau-4B might be a new locus for leaf rust and stripe rust resistance. The fourth QTL, QYr.hbau-7B is possibly a new QTL. The QTL identified in the present study with their flanking markers might be used for candidate gene mining and marker-assisted selection (MAS) in wheat breeding programs for rust resistance. [ABSTRACT FROM AUTHOR]

Diversification of cropping systems is a lever for the management of epidemics. However, most research to date has focused on cultivar mixtures, especially for cereals, even though crop mixtures can also improve disease management. To investigate the benefits of crop mixtures, we studied the effect of different crop mixture characteristics (i.e., companion proportion, sowing date, and traits) on the protective effect of the mixture. We developed a SEIR (Susceptible, Exposed, Infectious, Removed) model of two damaging wheat diseases (Zymoseptoria tritici and Puccinia triticina), which were applied to different canopy components, ascribable to wheat and a theoretical companion crop. We used the model to study the sensitivity of disease intensity to the following parameters: wheat-versus-companion proportion, companion sowing date and growth, and architectural traits. For both pathogens, the companion proportion had the strongest effect, with 25% of companion reducing disease severity by 50%. However, changing companion growth and architectural traits also significantly improved the protective effect. The effect of companion characteristics was consistent across different weather conditions. After decomposing the dilution and barrier effects, the model suggested that the barrier effect is maximized for an intermediate proportion of companion crop. Our study thus supports crop mixtures as a promising strategy to improve disease management. Future studies should identify real species and determine the combination of host and companion traits to maximize the protective effect of the mixture. [ABSTRACT FROM AUTHOR]

In order to screen the target proteins interacting with effector proteins of the wheat leaf rust and to lay a foundation for dissecting the defense response mechanism of the effector proteins interfering with hosts and disease resistance breeding, the samples of interaction between the isolate13-5-28-1 (JHKT) and susceptible wheat variety Thatcher at 0-12 d were collected. The three-frame homogenization was constructed by SMART method to screen the wheat cDNA library interacting with the wheat leaf rust. The homologous recombination method was used to construct the recombinant bait vector pGBKT7-Pt34084 of the effector factor Pt34084, and it was used as the bait protein to screen the interaction target protein by co-transformation method. The results showed that the cDNA library structure of the interaction between the wheat leaf rust and wheat was successfully constructed. The library capacity was about 1.05×107 CFU/mL, the titer was 1.2×109 CFU/mL, the average insertion fragment was more than 1 kb, and the recombination positive rate was 100%. The cDNA library met the requirement. The constructed bait recombinant vector pGBKT7-Pt34084 inhibited its self-activation after the addition of 20 mmol/L 3-AT and 400 ng/mL ABA to SD/-Trp-His-Ade medium. By this library a total of 16 different candidate interacting proteins from the wheat and the leaf rust were screened. These proteins were involved in plant metabolism, hormone signal transduction, plant disease resistance and other aspects. It indicated that Pt34084 could interfere with the host defense response and promote leaf rust infection through multiple pathways. The results are conducive to analyzing the pathogenic mechanism of wheat leaf rust and lay a foundation for creating new effective strategies to prevent and control wheat leaf rust. [ABSTRACT FROM AUTHOR]

Puccinia triticina (Pt) is an important pathogen of wheat. While breeding programmes develop resistant wheat cultivars to mitigate the effects of such rust-causing pathogens, the emergence of new rust races with wider virulence mandates the implementation of other control strategies. Our study investigated whether acidic pH conditions affected selected Carbohydrate-Active Enzymes (CAZymes) in Pt-inoculated Thatcher + Lr9 (IR) wheat compared to those found in the Thatcher (IS) wheat. The β-glucosidase and amyloglucosidase activity levels significantly increased in IR compared to the control from 1 to 14 days post-inoculation (dpi). In contrast, activity levels of invertase did not change in the IR wheat relative to the control at 1 and 7 dpi, but were significantly reduced in the IR plants at 14 dpi. The IS had higher activity of all three hexose-producing enzymes under acidic conditions. These enzyme activities could be increased in the IS to produce hexose sugars required by Pt to develop and advance infection. The phenotypic analysis supported this view because leaf rust disease symptoms were only visible in the IS plants. For cell wall loosening-related enzymes, the IR displayed higher activity of exoglucanase, xylanase and peroxidase enzymes compared to IS. The liquid chromatography–mass spectrometry analysis showed IR had higher concentrations of complex oligosaccharides compared to the IS. Thus, we concluded that the higher exoglucanase, xylanase and peroxidase activity could be involved in cell wall loosening under acidic conditions, while oligosaccharides could be building-blocks for synthesizing cell wall barriers that apprehend Pt growth in inoculated Thatcher + Lr9. [ABSTRACT FROM AUTHOR]

Wheat (Triticum aestivum L.) leaf rust is the most common and widely distributed wheat disease. Non‐destructive and real‐time methods for monitoring wheat leaf rust can help prevent and control plant diseases in agricultural production. In this study, we obtained multispectral imagery of the wheat canopy acquired by an unmanned aerial vehicle, selected the vegetation index using the K‐means algorithm (KA) and genetic algorithm (GA), and established a wheat leaf rust monitoring model based on the backpropagation neural network (BPNN) method. The results showed that the R2 and RMSE of the KA‐BPNN model were 0.902% and 5.45% for the modeling set, respectively, and 0.784% and 4.76% for the validation set, respectively; and the R2 and RMSE of the GA‐BPNN model was 0.922% and 4.88% for the modeling set, respectively, and 0.780% and 4.28% for the validation set, respectively. The prediction model after optimizing the variables using KA and GA had higher accuracy than the BPNN model, implying that using variable dimensionality reduction methods and complex machine learning algorithms to construct estimation models can improve model accuracy significantly. These models accurately monitored leaf rust in winter wheat, providing a theoretical basis and technical support for assessing plant diseases and screening disease‐resistant wheat varieties. [ABSTRACT FROM AUTHOR]

Abstract Wheat rusts, including stripe, leaf, and stem rusts, are severe wheat diseases and cause huge yield loss in China annually. Benefiting from utilizing the genetic resistance wheat varieties, wheat stem rust has been effectively controlled since the 1970s; however, the wheat stripe and leaf rusts are still threating the wheat production in China due to lack of effective agricultural regulations. This review summarizes the research advances on wheat rust physiology, epidemiology, and fungicide resistance in China. In addition, the corresponding field management strategies for the integrated control of rust diseases are also discussed.

Abstract Wheat (Triticum aestivum L.) leaf rust is the most common and widely distributed wheat disease. Non‐destructive and real‐time methods for monitoring wheat leaf rust can help prevent and control plant diseases in agricultural production. In this study, we obtained multispectral imagery of the wheat canopy acquired by an unmanned aerial vehicle, selected the vegetation index using the K‐means algorithm (KA) and genetic algorithm (GA), and established a wheat leaf rust monitoring model based on the backpropagation neural network (BPNN) method. The results showed that the R2 and RMSE of the KA‐BPNN model were 0.902% and 5.45% for the modeling set, respectively, and 0.784% and 4.76% for the validation set, respectively; and the R2 and RMSE of the GA‐BPNN model was 0.922% and 4.88% for the modeling set, respectively, and 0.780% and 4.28% for the validation set, respectively. The prediction model after optimizing the variables using KA and GA had higher accuracy than the BPNN model, implying that using variable dimensionality reduction methods and complex machine learning algorithms to construct estimation models can improve model accuracy significantly. These models accurately monitored leaf rust in winter wheat, providing a theoretical basis and technical support for assessing plant diseases and screening disease‐resistant wheat varieties.

Early crop disease detection is one of the most important tasks in plant protection. The purpose of this work was to evaluate the early wheat leaf rust detection possibility using hyperspectral remote sensing. The first task of the study was to choose tools for processing and analyze hyperspectral remote sensing data. The second task was to analyze the wheat leaf biochemical profile by chromatographic and spectrophotometric methods. The third task was to discuss a possible relationship between hyperspectral remote sensing data and the results from the wheat leaves, biochemical profile analysis. The work used an interdisciplinary approach, including hyperspectral remote sensing and data processing methods, as well as spectrophotometric and chromatographic methods. As a result, (1) the VIS-NIR spectrometry data analysis showed a high correlation with the hyperspectral remote sensing data; (2) the most important wavebands for disease identification were revealed (502, 466, 598, 718, 534, 766, 694, 650, 866, 602, 858 nm). An early disease detection accuracy of 97–100% was achieved from fourth dai (day/s after inoculation) using SVM. [ABSTRACT FROM AUTHOR]

Puccinia triticina is a major wheat pathogen worldwide. Although Iran is within the Fertile Crescent, which is supposed to be the center of origin of both wheat and P. triticina, the knowledge of the genetic variability of local populations of this basidiomycete is limited. We analyzed 12 inter simple sequence repeats (ISSRs) and 18 simple sequence repeats (SSRs) of 175 P. triticina isolates sampled between 2010 and 2017 from wheat and other Poaceae in 14 provinces of Iran. SSRs revealed more polymorphisms than ISSRs, indicating they were more effective in differentiating P. triticina populations. Based on a dissimilarity matrix with a variable mutation rate for SSRs and a Dice coefficient for ISSRs, the isolates were separated into three large groups, each including isolates from diverse geographic origins and hosts. The grouping of SSR genotypes in UPGMA dendrograms was consistent with the grouping inferred from the Bayesian approach. However, isolates with a common origin clustered into separate subgroups within each group. The high proportion of heterozygous alleles suggests that in Iran clonal reproduction prevails over sexual reproduction of the pathogen. A significant correlation was found between SSR and ISSR genotypes and the virulence phenotypes of the isolates, as determined in a previous study. [ABSTRACT FROM AUTHOR]

Wheat rusts, including stripe, leaf, and stem rusts, are severe wheat diseases and cause huge yield loss in China annually. Benefiting from utilizing the genetic resistance wheat varieties, wheat stem rust has been effectively controlled since the 1970s; however, the wheat stripe and leaf rusts are still threating the wheat production in China due to lack of effective agricultural regulations. This review summarizes the research advances on wheat rust physiology, epidemiology, and fungicide resistance in China. In addition, the corresponding field management strategies for the integrated control of rust diseases are also discussed. [ABSTRACT FROM AUTHOR]

In order to screen out the chemical agents for controlling wheat leaf rust, pyraclostrobin, epoxiconazole and their combinations with different proportions were evaluated in this study, and the indoor control efficacies on wheat leaf rust as protective agents were determined by spray inoculation method, the safety on wheat and the field control efficacy of wheat leaf rust of the optimal compound ratio for indoor screening were investigated. The results showed that pyraclostrobin, epoxiconazole and their combination had strong inhibitory effect on the lesion expansion of wheat leaf rust. Among them, pyraclostrobin had stronger inhibitory activity, and its EC50 value was 0.01 μg/mL. The results of joint toxicity evaluation showed that all combinations showed a synergistic additive efficacy, and the maximum synergistic coefficient was 1.50 with the mass ratio of pyraclostrobin epoxiconazole as 50:133. Both the indoor and field tests showed that the control efficacy was positively correlated with the established concentration gradient. In the field test with 120 a.i. g/hm2, the control efficacy of pyraclostrobin + epoxiconazole 26% SC was 85.12%, which was better than that of single-agent treatments. The safety evaluation tests showed that all treatments could make different varieties of wheat grow normally without drug damage. This study had shown that the combination of pyraclostrobin and epoxiconazole had a good control efficacy on wheat leaf rust, providing a theoretical basis for the prevention and control of wheat leaf rust and scientific medication in production. [ABSTRACT FROM AUTHOR]

The timely and accurate identification of stripe rust and leaf rust is essential in effective disease control and the safe production of wheat worldwide. To investigate methods for identifying the two diseases on different wheat varieties based on image processing technology, single-leaf images of the diseases on different wheat varieties, acquired under field and laboratory environmental conditions, were processed. After image scaling, median filtering, morphological reconstruction, and lesion segmentation on the images, 140 color, texture, and shape features were extracted from the lesion images; then, feature selections were conducted using methods including ReliefF, 1R, correlation-based feature selection, and principal components analysis combined with support vector machine (SVM), back propagation neural network (BPNN), and random forest (RF), respectively. For the individual-variety disease identification SVM, BPNN, and RF models built with the optimal feature combinations, the identification accuracies of the training sets and the testing sets on the same individual varieties acquired under the same image acquisition conditions as the training sets used for modeling were 87.18–100.00%, but most of the identification accuracies of the testing sets for other individual varieties were low. For the multi-variety disease identification SVM, BPNN, and RF models built with the merged optimal feature combinations based on the multi-variety disease images acquired under field and laboratory environmental conditions, identification accuracies in the range of 82.05–100.00% were achieved on the training set, the corresponding multi-variety disease image testing set, and all the individual-variety disease image testing sets. The results indicated that the identification of images of stripe rust and leaf rust could be greatly affected by wheat varieties, but satisfactory identification performances could be achieved by building multi-variety disease identification models based on disease images from multiple varieties under different environments. This study provides an effective method for the accurate identification of stripe rust and leaf rust and could be a useful reference for the automatic identification of other plant diseases. [ABSTRACT FROM AUTHOR]

Identification of resistance gene sources in seedling and adult plant stages is important to developing durable wheat cultivars. In this study, 100 genotypes of Aegilops tauschii, collected from natural habitats were evaluated in the experimental field of the Iraqi-mahaleh, Gorgan. Seeds were planted on one meter length lines and inoculated with Golestan leaf rust pathotypes in a randomized complete block design with three replications. The reaction of genotypes was also evaluated in greenhouse, by six Iranian pathotypes based on a completely randomized design with two replications in seed and plant improvement institute (SPII). To evaluate resistance in filed, we used infection type, AUDPC, final disease severity and coefficient of infection indices. The results showed that in greenhouse, the frequency of resistant, moderately resistant, moderately susceptible and susceptible genotypes were 7, 13, 13 and 67 percent, respectively. In field, the regarding frequencies were 14, 49, 7 and 30 percent. The correlation coefficient between final severity of infection, with the values of coefficient of infection and area under the disease progress curve, were 0.97 and 0.95, respectively. Accordingly, 57 genotypes with the desired characteristics, namely final infection intensity of 3.5-40, infection coefficient of 1.4-30 and rAUDPC, 1-32% were identified with MS and MR responses for resistance. Forty-six genotypes were susceptible in seedling stage and resistant in adult plant stage. Some genotypes originated from Afghanistan, Azerbaijan, China and Uzbekistan were resistant to all isolates which could be considered as appropriate sources of resistance to leaf rust disease for breeding of cultivated wheat species. [ABSTRACT FROM AUTHOR]

Eight wheat cultivars, Sakha-94, Giza-171, Sids-1, Sids-12, Sids-13, Shandweel-1, Misr-1, and Misr-2, were evaluated for leaf rust at the seedling and adult stages in the 2021 and 2022 seasons. Biochemical, histological, and genetic analyses were performed to determine the link between cultivars that were either sensitive or resistant to the disease. Misr-2 and Giza-171 cultivars had the highest levels of resistance to leaf rust races in 2021 (LTCGT, STSJT, and TTTST) and 2022 (MBGJT, TTTKS, and TTTTT) at the seedling stage. However, at the adult stage, Sakha-94, Giza-171, Misr-1, and Misr-2 cultivars had the highest levels of resistance; consequently, they had the lowest final disease severity and the lowest values of AUDPC. The correlation between the seedling reaction and adult reaction was non-significant, with values of 0.4401 and 0.4793 in the 2021 and 2022 seasons, respectively. Throughout the biochemical, histological, and genetic analyses, it was observed that catalase, peroxidase, and polyphenol oxidase activities significantly increased in the resistant cultivars. The discoloration of superoxide (O2-) and hydrogen peroxide (H2O2) significantly decreased in resistant and moderately resistant wheat cultivars (Sakha-94, Giza-171, Misr-1, and Misr-2); higher hydrogen peroxide (H2O2) and superoxide (O2-) levels were recorded for the susceptible cultivars compared to the resistant cultivars. Molecular markers proved that the Lr50 gene was detected in the resistant cultivars. Puccinia triticina infections negatively affected most histological characteristics of flag leaves, especially in susceptible cultivars. The thickness of the blade (µ), the thickness of the upper and lower epidermis (UE and LE), the thickness of mesophyll tissue (MT), and bundle length and width in the midrib were decreased in susceptible cultivars such as Sids-1, Sids-13, and Shandwel-1 compared with resistant cultivars.

Two new variants of Puccinia triticina were identified in the repository cultures of pathotypes 20 (5R27 = SGQPL) and 107‐1 (45R35 = JCGPL) being maintained as live cultures in the national repository at Shimla, Himachal Pradesh, India, for 87 and 24 years, respectively. Mixtures of infection types were observed on Lr15 in one pathotype 20 whereas on Lr3 in 107‐1. The single pustule isolations and further purification in both the cases yielded two new pathotypes designated as 20‐2 (57R27 = SHKPL) and 57 (45R39 = KGTPL). The pathotype 20‐2 was one‐step gain in virulence to Lr15 in mother culture of pathotype 20. Contrarily, the second new pathotype though close to 107‐1 (with additional virulence to Lr3), however, resembled standard race 57 of the classical differentials. The difference in virulence on one gene as compared to the respective mother culture and their non‐detection from the field samples reflects mutation for virulence in situ. To confirm the novelty of new pathotypes, detailed studies were conducted on differentials, avirulence/virulence on Lr genes, DNA polymorphism using SSR markers, and the results are presented in this publication. The new variants have been added to the live culture collection of the centre and designated as PrtI 57 and PrtI 20‐2. [ABSTRACT FROM AUTHOR]

The pathogenicity‐related traits of biotrophic plant pathogens are usually measured on the individual host plant, at the scale of a single pathogen life cycle, whereas epidemic development in the field encompasses a succession of cycles. It remains unclear which traits make the greatest contribution to pathogen fitness in the field and to epidemic severity. The objective of this study was to determine the contributions of elementary pathogenicity traits to epidemic development in field conditions. We challenged a set of wheat cultivars with three different leaf rust isolates, under both controlled and field conditions, in 3 consecutive years. Infection efficiency, latent period, lesion size, spore production per lesion and spore production capacity were measured in the greenhouse, whereas disease severity was measured in the field. Most, but not all, of the pathogenicity traits were related to each other. All traits contributed to epidemic development in the field, but to different extents. Surprisingly, lesion size and spore production per lesion were inversely correlated with epidemic severity. Conversely, there was a strong positive correlation between spore production capacity and pathogen fitness in the field, in accordance with the concept of propagule pressure as a strong determinant of invasion success. Severe epidemics were mostly associated with small lesions with a high spore production capacity, high infection efficiency and a short latent period. [ABSTRACT FROM AUTHOR]

Early crop disease detection is one of the most important tasks in plant protection. The purpose of this work was to evaluate the early wheat leaf rust detection possibility using hyperspectral remote sensing. The first task of the study was to choose tools for processing and analyze hyperspectral remote sensing data. The second task was to analyze the wheat leaf biochemical profile by chromatographic and spectrophotometric methods. The third task was to discuss a possible relationship between hyperspectral remote sensing data and the results from the wheat leaves, biochemical profile analysis. The work used an interdisciplinary approach, including hyperspectral remote sensing and data processing methods, as well as spectrophotometric and chromatographic methods. As a result, (1) the VIS-NIR spectrometry data analysis showed a high correlation with the hyperspectral remote sensing data; (2) the most important wavebands for disease identification were revealed (502, 466, 598, 718, 534, 766, 694, 650, 866, 602, 858 nm). An early disease detection accuracy of 97–100% was achieved from fourth dai (day/s after inoculation) using SVM.

The timely and accurate identification of stripe rust and leaf rust is essential in effective disease control and the safe production of wheat worldwide. To investigate methods for identifying the two diseases on different wheat varieties based on image processing technology, single-leaf images of the diseases on different wheat varieties, acquired under field and laboratory environmental conditions, were processed. After image scaling, median filtering, morphological reconstruction, and lesion segmentation on the images, 140 color, texture, and shape features were extracted from the lesion images; then, feature selections were conducted using methods including ReliefF, 1R, correlation-based feature selection, and principal components analysis combined with support vector machine (SVM), back propagation neural network (BPNN), and random forest (RF), respectively. For the individual-variety disease identification SVM, BPNN, and RF models built with the optimal feature combinations, the identification accuracies of the training sets and the testing sets on the same individual varieties acquired under the same image acquisition conditions as the training sets used for modeling were 87.18–100.00%, but most of the identification accuracies of the testing sets for other individual varieties were low. For the multi-variety disease identification SVM, BPNN, and RF models built with the merged optimal feature combinations based on the multi-variety disease images acquired under field and laboratory environmental conditions, identification accuracies in the range of 82.05–100.00% were achieved on the training set, the corresponding multi-variety disease image testing set, and all the individual-variety disease image testing sets. The results indicated that the identification of images of stripe rust and leaf rust could be greatly affected by wheat varieties, but satisfactory identification performances could be achieved by building multi-variety disease identification models based on disease images from multiple varieties under different environments. This study provides an effective method for the accurate identification of stripe rust and leaf rust and could be a useful reference for the automatic identification of other plant diseases.

Non‐host resistance is the resistance of plants against all so‐called non‐adapted pathogens, and is considered the most durable and efficient immune system of plants. We investigated barley powdery mildew (Blumeria graminis f.sp. hordei, Bgh)‐triggered defence responses in seven wheat genotypes, and the induction of resistance by this non‐host pathogen to challenge infection with leaf rust, Puccinia triticina Eriks (formerly known as Puccinia recondita f.sp. tritici). Bright‐field and ultraviolet microscopy revealed that although the germination of conidia on non‐host wheat leaves was generally lower than on host barley leaves, the 100% germination on Mv Mambó and only 50% germination on Mv 1 wheat genotypes are the two extremes. If we consider only the germinated conidia, papilla formation was the most frequently observed interaction on Mv 2 (90%) and Mv 4 (88%) genotypes. Epidermal cell death was pronounced on Mv Mambó (31%), but rare on Mv 2 (10%) and Mv 4 (11%), and a mesophyll hypersensitive response could even be detected. At sites of penetration attempts accumulation of H2O2 was shown by 3,3′‐diaminobenzidine staining. Ascorbate peroxidase, glutathione S‐transferase and catalase enzyme activities were augmented by 24.5%, 40.4%, and 21.5%, respectively, in wheat leaves 2 days after Bgh infection. Primary inoculation with Bgh, although with high variability, reduced the number of pustules in all wheat genotypes at first and third leaf stages upon inoculation with leaf rust races 12 and 61 by 10%–70% depending on the genotype, leaf stage and rust race. [ABSTRACT FROM AUTHOR]

Abstract Background Wheat leaf rust is an important disease worldwide. Understanding the pathogenic molecular mechanism of Puccinia triticina Eriks. (Pt) and the inconstant toxic region is critical for managing the disease. The present study aimed to analyze the pathogenic divergence between Pt isolates. Results Total RNA was extracted from the wheat cultivar Thatcher infected by two Pt isolates, Tc361_1 (THTT) and Tc284_2 (THTS), at 144 h post inoculation (hpi). The mRNA was then sequenced, and a total of 2784 differentially expressed genes (DEGs) were detected. Forty-five genes were specifically expressed in THTT; these genes included transcription initiation factors and genes with transmembrane transporter activity and other genes. Twenty-six genes were specifically expressed in THTS, including genes with GTPase activity, ABC transporters and other genes. Fifty-four differentially expressed candidate effectors were screened from the two isolates. Two candidate effectors were chosen and validated on tobacco, and the results showed that they could inhibit necrosis induced by BAX. qRT-PCR of 12 significant DEGs was carried out to validate that the results are similar to those of RNA-seq at 144 hpi, to show the expression levels of these DEGs in the early stage and to elucidate the differences in expression between the two Pt pathotypes. Conclusion The results obtained in this study showed that although the two pathotypes of THTT and THTS contribute similar virulence to wheat, there are a large number of genes participate in the interaction with the susceptible wheat cultivar Thatcher, and revealed the pathogenicity of rust is very complicated.

Plant pathogens are responsible for the annual yield loss of crops worldwide and pose a significant threat to global food security. A necessary prelude to many plant disease epidemics is the shortrange dispersal of spores, which may generate several disease foci within a field. New information is needed on the mechanisms of plant pathogen spread within and among susceptible plants. Here, we show that self-propelled jumping dew droplets, working synergistically with low wind flow, can propel spores of a fungal plant pathogen (wheat leaf rust) beyond the quiescent boundary layer and disperse them onto neighboring leaves downwind. An array of horizontal water-sensitive papers was used to mimic healthy wheat leaves and showed that up to 25 spores/h may be deposited on a single leaf downwind of the infected leaf during a single dew cycle. These findings reveal that a single dew cycle can disperse copious numbers of fungal spores to other wheat plants, even in the absence of rain splash or strong gusts of wind. [ABSTRACT FROM AUTHOR]

Despite the global economic importance of the wheat leaf rust pathogen Puccinia triticina (Pt), genomic resources for Pt are limited and chromosome-level assemblies of Pt are lacking. Here, we present a complete haplotype-resolved genome assembly at a chromosome-scale for Pt using the Australian pathotype 64-(6),(7),(10),11 (Pt64; North American race LBBQB) built upon the newly developed technologies of PacBio and Hi-C sequencing. PacBio reads with ∼200-fold coverage (29.8 Gb data) were assembled by Falcon and Falcon-unzip and subsequently scaffolded with Hi-C data using Falcon-phase and Proximo. This approach allowed us to construct 18 chromosome pseudomolecules ranging from 3.5 to 12.3 Mb in size for each haplotype of the dikaryotic genome of Pt64. Each haplotype had a total length of ∼147 Mb, scaffold N 50 of ∼9.4 Mb, and was ∼93% complete for BUSCOs. Each haplotype had ∼29,800 predicted genes, of which ∼2,000 were predicted as secreted proteins (SPs). The investigation of structural variants (SVs) between haplotypes A and B revealed that 10% of the total genome was spanned by SVs, highlighting variations previously undetected by short-read based assemblies. For the first time, the mating type (MAT) genes on each haplotype of Pt64 were identified, which showed that MAT loci a and b are located on two chromosomes (chromosomes 7 and 14), representing a tetrapolar type. Furthermore, the Pt64 assembly enabled haplotype-based evolutionary analyses for 21 Australian Pt isolates, which highlighted the importance of a haplotype resolved reference when inferring genetic relationships using whole genome SNPs. This Pt64 assembly at chromosome-scale with full phase information provides an invaluable resource for genomic and evolutionary research, which will accelerate the understanding of molecular mechanisms underlying Pt -wheat interactions and facilitate the development of durable resistance to leaf rust in wheat and sustainable control of rust disease. [ABSTRACT FROM AUTHOR]

Despite the global economic importance of the wheat leaf rust pathogen Puccinia triticina (Pt), genomic resources for Pt are limited and chromosome-level assemblies of Pt are lacking. Here, we present a complete haplotype-resolved genome assembly at a chromosome-scale for Pt using the Australian pathotype 64-(6),(7),(10),11 (Pt64; North American race LBBQB) built upon the newly developed technologies of PacBio and Hi-C sequencing. PacBio reads with ∼200-fold coverage (29.8 Gb data) were assembled by Falcon and Falcon-unzip and subsequently scaffolded with Hi-C data using Falcon-phase and Proximo. This approach allowed us to construct 18 chromosome pseudomolecules ranging from 3.5 to 12.3 Mb in size for each haplotype of the dikaryotic genome of Pt64. Each haplotype had a total length of ∼147 Mb, scaffold N50 of ∼9.4 Mb, and was ∼93% complete for BUSCOs. Each haplotype had ∼29,800 predicted genes, of which ∼2,000 were predicted as secreted proteins (SPs). The investigation of structural variants (SVs) between haplotypes A and B revealed that 10% of the total genome was spanned by SVs, highlighting variations previously undetected by short-read based assemblies. For the first time, the mating type (MAT) genes on each haplotype of Pt64 were identified, which showed that MAT loci a and b are located on two chromosomes (chromosomes 7 and 14), representing a tetrapolar type. Furthermore, the Pt64 assembly enabled haplotype-based evolutionary analyses for 21 Australian Pt isolates, which highlighted the importance of a haplotype resolved reference when inferring genetic relationships using whole genome SNPs. This Pt64 assembly at chromosome-scale with full phase information provides an invaluable resource for genomic and evolutionary research, which will accelerate the understanding of molecular mechanisms underlying Pt-wheat interactions and facilitate the development of durable resistance to leaf rust in wheat and sustainable control of rust disease.

Identifying resistance related metabolites as biomarker for screening wheat germplasms resistant to leaf rust (Puccinia triticina ) is a useful approach to increase the speed, accuracy and cost effectiveness of screening disease resistance. The relatively polar metabolites were extracted in a mixture of methanol-water from near isogenic line (NILs) of wheat susceptible (Thatcher Lr22b) or resistant (Thatcher Lr25) to leaf rust in the two leaf stage, 24 h after inoculation with the pathogen, talcum powder or sterilized distilled water, in three replications. Metabolites were analyzed using a GC/MS. ANOVA showed that abundance of 26 metabolites had significant differences among experimental factors including near isogenic lines (NILs), inoculation (I) and NILs ×I interaction. Abundance of 26 significant metabolites was subjected to canonical discriminant analysis and hierarchical cluster analysis to group observations of metabolite profiles based on similarities and differences in the investigated metabolic space. Finally 13 resistance related metabolites (RR) and 13 Pathogenesis related metabolites (PR) were identified that the majority of RR metabolites involved in induced resistance and constitutive resistance. Significant metabolites included metabolites with potential signaling and/or antimicrobial activity as well as molecules used as precursors for cell wall reinforcement, phenolic and alkaloids compounds, and accumulation of amino acids and proteins associated with resistance. Up-regulation of the number pathways upon infection of wheat to leaf rust fungus is discussed. [ABSTRACT FROM AUTHOR]

Wheat leaf rust, caused by Puccinia triticina (Pt), is an important foliar disease that has an important influence on wheat yield. The most economic, safe and effective way to control the disease is growing resistant cultivars. In the present study, a total of 46 wheat landraces and 34 wheat lines with known Lr (leaf rust resistance) genes were inoculated with 16 Pt pathotypes for postulating seedling resistance gene(s) in the greenhouse. These cultivars and five wheat differential lines with adult plant resistance (APR) genes (Lr12, Lr22b, Lr34, Lr35 and Lr37) were also evaluated for identification of slow rusting resistance in the field trials in Baoding, Hebei Province of China in the 2014–2015 and 2015–2016 cropping seasons. Furthermore, 10 functional molecular markers closely linked to 10 known Lr genes were used to detect all the wheat genotypes. Results showed that most of the landraces were susceptible to most of the Pt pathotypes at seedling stage. Nonetheless, Lr1 was detected only in Hongtangliangmai. The field experimental test of the two environments showed that 38 landraces showed slow rusting resistance. Seven cultivars possessed Lr34 but none of the landraces contained Lr37 and Lr46. Lr genes namely, Lr9, Lr19, Lr24, Lr28, Lr29, Lr47, Lr51 and Lr53 were effective at the whole plant stage. Lr18, Lr36 and Lr45 had lost resistance to part of pathotypes at the seedling stage but showed high resistance at the adult plant stage. Lr34 as a slowing rusting gene showed good resistance in the field. Four race-specific APR genes Lr12, Lr13, Lr35 and Lr37 conferred good resistance in the field experiments. Seven race-specific genes, Lr2b, Lr2c, Lr11, Lr16, Lr26, Lr33 and LrB had lost resistance. The 38 landraces showed slow rusting resistance to wheat leaf rust can be used as resistance resources for wheat resistance breeding in China.

Abstract Five plant extracts, i.e., henna, Lawsonia inermis; acalypha, Acalypha wilkesiana; chinaberry, Melia azedarach; pomegranate, Punica granatum; and lantana, Lantana camara, were tested as inducers to protect wheat against leaf rust infection caused by Puccinia triticina Eriks. The plant extracts were applied pre-infection on susceptible wheat cultivar "Gemmiza-7" under field conditions during two growing seasons (2016/2017 and 2017/2018). All the tested plant extracts were found to be effective against the leaf rust infection. They significantly reduced the coefficient of infection (ACI) to be ranging 7.50 to 20.00, compared to the non-treated control (ACI = 75.00). Lantana extract was the most effective one (efficiency = 88.88%), which was very close to the fungicide “diniconazole” (efficiency = 89.92%). Henna extract ranked second (80.00%), followed by chinaberry (76.00%), acalypha (72.00%), and pomegranate (68.00%). However, wheat yield components were significantly increased by all the tested treatments, especially lantana extract and the fungicide. Similarly, biochemical analyses revealed a significant increase in the plant contents of chlorophyll a and b, total phenolics, and oxidative enzymes activities (POX and PPO) at all the tested treatments. Results indicated that the tested plant extracts could induce wheat resistance to leaf rust.

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This study provides a bio-economic assessment of the global climate suitability and probabilistic crop-loss estimates attributable to wheat leaf rust. We draw on a purpose-built, spatially explicit, ecoclimatic suitability model for wheat leaf rust to estimate that 94.4% of global wheat production is vulnerable to the disease. To reflect the spatiotemporal variation in leaf rust losses, we used a probabilistic approach to estimate a representative rust loss distribution based on long-term, state-level annual U.S. loss estimates. Applying variants of this representative loss distribution to selected wheat production areas in 15 epidemiological zones throughout the world, we project global annual average losses of 8.6 million metric tons of grain for the period 2000 to 2050 based on a conservative, baseline scenario, and 18.3 million metric tons based on a high-loss scenario; equivalent to economic losses ranging from $1.5 to $3.3 billion per year (2016 U.S. prices). Even the more conservative baseline estimate implies that a sustained, worldwide investment of $50.5 million per year in leaf rust research is economically justified. [ABSTRACT FROM AUTHOR]

Rust fungi secrete various specialized effectors into host cells to manipulate the plant defense response. Conserved motifs, including RXLR, LFLAK-HVLVxxP (CRN), Y/F/WxC, CFEM, LysM, EAR, [SG]-P-C-[KR]-P, DPBB_1 (PNPi), and ToxA, have been identified in various oomycete and fungal effectors and are reported to be crucial for effector translocation or function. However, little is known about potential effectors containing any of these conserved motifs in the wheat leaf rust fungus (Puccinia triticina, Pt). In this study, sequencing was performed on RNA samples collected from the germ tubes (GT) of uredospores of an epidemic Pt pathotype PHTT(P) and Pt-infected leaves of a susceptible wheat cultivar “Chinese Spring” at 4, 6, and 8 days post-inoculation (dpi). The assembled transcriptome data were compared to the reference genome of “Pt 1-1 BBBD Race 1.” A total of 17,976 genes, including 2,284 “novel” transcripts, were annotated. Among all these genes, we identified 3,149 upregulated genes upon Pt infection at all time points compared to GT, whereas 1,613 genes were more highly expressed in GT. A total of 464 secreted proteins were encoded by those upregulated genes, with 79 of them also predicted as possible effectors by EffectorP. Using hmmsearch and Regex, we identified 719 RXLR-like, 19 PNPi-like, 19 CRN-like, 138 Y/F/WxC, and 9 CFEM effector candidates from the deduced protein database including data based on the “Pt 1-1 BBBD Race 1” genome and the transcriptome data collected here. Four of the PNPi-like effector candidates with DPBB_1 conserved domain showed physical interactions with wheat NPR1 protein in yeast two-hybrid assay. Nine Y/F/WxC and seven CFEM effector candidates were transiently expressed in Nicotiana benthamiana. None of these effector candidates showed induction or suppression of cell death triggered by BAX protein, but the expression of one CFEM effector candidate, PTTG_08198, accelerated the progress of cell death and promoted the accumulation of reactive oxygen species (ROS). In conclusion, we profiled genes associated with the infection process of the Pt pathotype PHTT(P). The identified effector candidates with conserved motifs will help guide the investigation of virulent mechanisms of leaf rust fungus.

Leaf rust, caused by Puccinia triticina (Pt), is one of the most devastating diseases of wheat, affecting production in nearly all wheat-growing regions worldwide. Despite its economic importance, genomic resources for Pt are very limited. In the present study, we have used long-read sequencing (LRS) and the pipeline of FALCON and FALCON-Unzip (v4.1.0) to carry out the first LRS-based de novo genome assembly for Pt. Using 22.4-Gb data with an average read length of 11.6 kb and average coverage of 150-fold, we generated a genome assembly for Pt104 [strain 104-2,3,(6),(7),11; isolate S423], considered to be the founding isolate of a clonal lineage of Pt in Australia. The Pt104 genome contains 162 contigs with a total length of 140.5 Mb and N50 of 2 Mb, with the associated haplotigs providing haplotype information for 91% of the genome. This represents the best quality of Pt genome assembly to date, which reduces the contig number by 91-fold and improves the N50 by 4-fold as compared to the previous Pt race1 assembly. An annotation pipeline that combined multiple lines of evidence including the transcriptome assemblies derived from RNA-Seq, previously identified expressed sequence tags and Pt race 1 protein sequences predicted 29,043 genes for Pt104 genome. Based on the presence of a signal peptide, no transmembrane segment, and no target location to mitochondria, 2,178 genes were identified as secreted proteins (SPs). Whole-genome sequencing (Illumina paired-end) was performed for Pt104 and six additional strains with differential virulence profile on the wheat leaf rust resistance genes Lr26, Lr2a, and Lr3ka. To identify candidates for the corresponding avirulence genes AvrLr26, AvrLr2a, and AvrLr3ka, genetic variation within each strain was first identified by mapping to the Pt104 genome. Variants within predicted SP genes between the strains were then correlated to the virulence profiles, identifying 38, 31, and 37 candidates for AvrLr26, AvrLr2a, and AvrLr3ka, respectively. The identification of these candidate genes lays a good foundation for future studies on isolating these avirulence genes, investigating the molecular mechanisms underlying host–pathogen interactions, and the development of new diagnostic tools for pathogen monitoring.

Aim of study: To analyze the structure of P. triticina populations by a virulence survey in the North Caucasus region of Russia from 2011 to 2015. Area of study: The North Caucasus region is a leading grain production region in Russia where wheat leaf rust causes losses in yield. Material and methods: Uredinial samples of leaf rust were collected in all agro-climatic zones of the North Caucasus on the production sites of winter wheat and on the plots of official state trials. Single uredinial isolates (a total of 564) were tested for virulence with 41 ˈThatcherˈ near isogenic lines with Lr resistance genes. Main results: Clones virulent to Lr9, Lr42, Lr47 and Lr50 were not found. Isolates virulent to the Lr19, Lr24, Lr29, Lr41, Lr43 + 24, Lr45, Lr52 genes were characterized by low frequencies. The 564 fungal isolates studied were represented by 564 virulence phenotypes, the majority of them with a virulence complexity from 9 to 19. A high level of intrapopulation fungus diversity in virulence was noticed during the whole period of research (Shannon diversity index from 2.994 to 3.314). The differences in the frequencies of virulences in the years of research were small (Rogers distance from 0.001 to 0.160). Research highlights: Due to the fact that the North Caucasus region is a zone of epiphytotic danger and high variability of the P. triticina population, the analysis of the genetics of the fungus population is important for the strategy of varietal distribution in the region and development of rust-resistant varieties.

Puccinia triticina, the causal agent of wheat leaf rust, is one of the most devastating rust fungi attacking wheat worldwide. Seventy-six isolates of the wheat leaf rust pathogen from Yunnan, Sichuan, Gansu and Henan provinces, China, were tested on wheat leaf rust differentials and the population structure was analyzed using four presumably neutral partial sequence markers such as elongation factor-1α (EF-1α), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), β-tubulin (TUB) and the second largest RNA polymerase subunit (RPB2). The phenotypic diversity of Yunnan and Sichuan populations was higher than that of Gansu and Henan populations. The four populations were separated into two clusters based on the pathogenic data. A total of 12 single nucleotide polymorphisms (SNPs) and 32 haplotypes were identified among the four sequences. The 32 haplotypes were divided into two clusters in a neighbor-joining tree. Bayesian analyses also identified two clusters. Pairwise FST between populations in different regions were significantly different (P

Leaf rust is one of the most significant diseases of wheat worldwide. In Argentina, it is one of the main reasons for variety replacement that becomes susceptible after large-scale use. Some varieties showed durable resistance to this disease, including Buck Manantial and Sinvalocho MA. RILs (Recombinant Inbred Lines) were developed for each of these varieties and used in genetics studies to identify components of resistance, both in greenhouse inoculations using leaf rust races, and in field evaluations under natural population infections. In Buck Manantial, the APR gene LrBMP1 was associated with resistance in field tests. In crosses involving Sinvalocho MA, four genes were previously identified and associated with resistance in field testing: APR (Adult Plant Resistance) gene LrSV1, the APR genetic system LrSV2 + LrcSV2 and the ASR (All Stage Resistance) gene LrG6. Using backcrosses, LrBMP1 was introgressed in four commercial susceptible varieties and LrSV1, LrSV2 + LrcSV2 and LrG6 were simultaneously introgressed in three susceptible commercial varieties. The use of molecular markers for recurrent parent background selection allowed us to select resistant lines with more than 80% similarity to commercial varieties. Additionally, progress towards positional cloning of the genetic system LrSV2 + LrcSV2 for leaf rust APR is reported.

Leaf rust, caused by Puccinia triticina (Pt), is one of the most devastating diseases of wheat, affecting production in nearly all wheat-growing regions worldwide. Despite its economic importance, genomic resources for Pt are very limited. In the present study, we have used long-read sequencing (LRS) and the pipeline of FALCON and FALCON-Unzip (v4.1.0) to carry out the first LRS-based de novo genome assembly for Pt. Using 22.4-Gb data with an average read length of 11.6 kb and average coverage of 150-fold, we generated a genome assembly for Pt104 [strain 104-2,3,(6),(7),11; isolate S423], considered to be the founding isolate of a clonal lineage of Pt in Australia. The Pt104 genome contains 162 contigs with a total length of 140.5 Mb and N50 of 2 Mb, with the associated haplotigs providing haplotype information for 91% of the genome. This represents the best quality of Pt genome assembly to date, which reduces the contig number by 91-fold and improves the N50 by 4-fold as compared to the previous Pt race1 assembly. An annotation pipeline that combined multiple lines of evidence including the transcriptome assemblies derived from RNA-Seq, previously identified expressed sequence tags and Pt race 1 protein sequences predicted 29,043 genes for Pt104 genome. Based on the presence of a signal peptide, no transmembrane segment, and no target location to mitochondria, 2,178 genes were identified as secreted proteins (SPs). Whole-genome sequencing (Illumina paired-end) was performed for Pt104 and six additional strains with differential virulence profile on the wheat leaf rust resistance genes Lr26 , Lr2a , and Lr3ka. To identify candidates for the corresponding avirulence genes AvrLr26 , AvrLr2a , and AvrLr3ka , genetic variation within each strain was first identified by mapping to the Pt104 genome. Variants within predicted SP genes between the strains were then correlated to the virulence profiles, identifying 38, 31, and 37 candidates for AvrLr26 , AvrLr2a , and AvrLr3ka , respectively. The identification of these candidate genes lays a good foundation for future studies on isolating these avirulence genes, investigating the molecular mechanisms underlying host–pathogen interactions, and the development of new diagnostic tools for pathogen monitoring. [ABSTRACT FROM AUTHOR]

Rust fungi secrete various specialized effectors into host cells to manipulate the plant defense response. Conserved motifs, including RXLR, LFLAK-HVLVxxP (CRN), Y/F/WxC, CFEM, LysM, EAR, [SG]-P-C-[KR]-P, DPBB_1 (PNPi), and ToxA, have been identified in various oomycete and fungal effectors and are reported to be crucial for effector translocation or function. However, little is known about potential effectors containing any of these conserved motifs in the wheat leaf rust fungus (Puccinia triticina , Pt). In this study, sequencing was performed on RNA samples collected from the germ tubes (GT) of uredospores of an epidemic Pt pathotype PHTT(P) and Pt -infected leaves of a susceptible wheat cultivar "Chinese Spring" at 4, 6, and 8 days post-inoculation (dpi). The assembled transcriptome data were compared to the reference genome of " Pt 1-1 BBBD Race 1." A total of 17,976 genes, including 2,284 "novel" transcripts, were annotated. Among all these genes, we identified 3,149 upregulated genes upon Pt infection at all time points compared to GT, whereas 1,613 genes were more highly expressed in GT. A total of 464 secreted proteins were encoded by those upregulated genes, with 79 of them also predicted as possible effectors by EffectorP. Using hmmsearch and Regex, we identified 719 RXLR-like, 19 PNPi-like, 19 CRN-like, 138 Y/F/WxC, and 9 CFEM effector candidates from the deduced protein database including data based on the " Pt 1-1 BBBD Race 1" genome and the transcriptome data collected here. Four of the PNPi-like effector candidates with DPBB_1 conserved domain showed physical interactions with wheat NPR1 protein in yeast two-hybrid assay. Nine Y/F/WxC and seven CFEM effector candidates were transiently expressed in Nicotiana benthamiana. None of these effector candidates showed induction or suppression of cell death triggered by BAX protein, but the expression of one CFEM effector candidate, PTTG_08198, accelerated the progress of cell death and promoted the accumulation of reactive oxygen species (ROS). In conclusion, we profiled genes associated with the infection process of the Pt pathotype PHTT(P). The identified effector candidates with conserved motifs will help guide the investigation of virulent mechanisms of leaf rust fungus. [ABSTRACT FROM AUTHOR]

Background: Wheat leaf rust is an important disease worldwide. Understanding the pathogenic molecular mechanism of Puccinia triticina Eriks. (Pt) and the inconstant toxic region is critical for managing the disease. The present study aimed to analyze the pathogenic divergence between Pt isolates. Results: Total RNA was extracted from the wheat cultivar Thatcher infected by two Pt isolates, Tc361_1 (THTT) and Tc284_2 (THTS), at 144 h post inoculation (hpi). The mRNA was then sequenced, and a total of 2784 differentially expressed genes (DEGs) were detected. Forty-five genes were specifically expressed in THTT; these genes included transcription initiation factors and genes with transmembrane transporter activity and other genes. Twenty-six genes were specifically expressed in THTS, including genes with GTPase activity, ABC transporters and other genes. Fifty-four differentially expressed candidate effectors were screened from the two isolates. Two candidate effectors were chosen and validated on tobacco, and the results showed that they could inhibit necrosis induced by BAX. qRT-PCR of 12 significant DEGs was carried out to validate that the results are similar to those of RNA-seq at 144 hpi, to show the expression levels of these DEGs in the early stage and to elucidate the differences in expression between the two Pt pathotypes. Conclusion: The results obtained in this study showed that although the two pathotypes of THTT and THTS contribute similar virulence to wheat, there are a large number of genes participate in the interaction with the susceptible wheat cultivar Thatcher, and revealed the pathogenicity of rust is very complicated. [ABSTRACT FROM AUTHOR]

Leaf rust resistance is of high importance for a sustainable European wheat production. The expression of known resistance genes starts at different developmental stages of wheat. Breeding for resistance can be supported by a fast, precise, and resource-saving phenotyping. The examination of detached leaf assays of juvenile plants inoculated under controlled conditions and phenotyped by a robotic- and computer-based, high-throughput system is a promising approach in this respect. Within this study, the validation of the phenotyping workflow was conducted based on a winter wheat set derived from Central Europe and examined at different plant developmental stages. Moderate Pearson correlations of 0.38–0.45 comparing leaf rust resistance of juvenile and adult plants were calculated and may be mainly due to different environmental conditions. Specially, the infection under controlled conditions was limited by the application of a single rust race at only one time point. Our results suggest that the diversification with respect to the applied rust race spectrum is promising to increase the consistency of detached leaf assays and the transferability of its results to the field.

Leaf rust caused by Puccinia recondita f. sp. tritici belongs to the most important diseases of wheat worldwide. The progress of the disease is highly dependent on meteorological conditions. One of the parameters affecting the disease progress is latency period driven mostly by temperature. Examination of the influence of predicted temperature changes on the monthly sum of the daily latency period expressed as rate (MSLPR) in western Poland was the aim of our study. Experiments in quasi-natural conditions were performed with the aim of validating models describing the influence of temperature on leaf rust latency period in two wheat varieties, Turnia and Ostroga. Both models used for assessment of latency period duration on cv. Turnia and cv. Ostroga performed well. The influence of climate changes on leaf rust latency period was then simulated using meteorological data from three weather stations located in western Poland and virtual data obtained after transformation of the recorded data to reflect a temperature changes under RCP2.6 and RCP8.5 scenarios according to giss_e2_r climate model. The study shows that without mitigation of greenhouse gas emission latency period of wheat leaf rust is going to decrease which may result in increase of wheat leaf rust incidence.

Wheat leaf rust, caused by Puccinia triticina f. sp. tritici ( Pt ), is distributed widely in wheat-producing areas and results in serious yield losses worldwide. In China, leaf rust has been largely controlled with a demethylation inhibitor (DMI) fungicide, triadimefon. Although high levels of fungicide resistance in pathogens have been reported, no field failure of wheat leaf rust to DMI fungicides has been reported in China. A resistance risk assessment of triadimefon to Pt was investigated in the present study. The sensitivity of 197 Pt isolates across the country to triadimefon was determined, and the density distribution of EC 50 values (concentration at which mycelial growth is inhibited by 50%) showed a continuous multimodal curve because of the extensive use of this fungicide in wheat production, with a mean value of 0.46 μg/ml. The majority of the tested Pt isolates were sensitive to triadimefon, whereas 10.2% developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. No correlation was observed between triadimefon and tebuconazole and hexaconazole, which have the similar mode of action, or pyraclostrobin and flubeneteram, which have different modes of action. Overexpression of the target gene Cyp51 led to the triadimefon resistance of Pt . The risk of resistance to triadimefon in Pt may be low to moderate. This study provided important data for fungicide resistance risk management against wheat leaf rust., Competing Interests: The author(s) declare no conflict of interest.

Highlights • Addressing the effects of different LAI values on the accuracy of the selected machine learning methods in retrieval of wheat leaf rust severity level. • Provide separate wavelength ranges with the highest contributions in the wheat leaf rust inversion model at the three LAI levels. Abstract Accurate diagnosis of wheat leaf rust is of high interest for precision farming. Spectral data have been increasingly employed to detect this disease at leaf or canopy scales; however, less attention has been paid to the variations of leaf area index (LAI). Therefore, in this study, identification of wheat leaf rust was investigated at canopy scale and under different LAI levels, namely high, medium and low. Four machine learning (ML) methods including ν -support vector regression (ν -SVR), boosted regression trees (BRT), random forests regression (RFR) and Gaussian process regression (GPR) were built to estimate disease severity (DS) levels at canopy scale, where the reflectance data were measured in field situ by using a spectroradiometer, in which records spectra from 350 to 2500 nm. Results showed that ν -SVR outperformed the other ML methods at all three LAI levels with the R 2 measures all being around 0.99. The results, particularly, showed that the performances of the ML methods were improved with increasing LAI value, where RFR reported the worst R 2 value of 0.79 (RMSE = 8.5%) at low LAI level. The variable importance obtained using BRT showed three distinct regions of wavelengths that were appropriate across different LAI levels. The results of this research confirmed that hyperspectral signature can be reliably considered to identify wheat leaf rust disease at different LAI levels. Moreover, performances of several spectral vegetation indices (SVIs) were compared with those of the ML techniques. The results showed that the SVIs were consistently outperformed by the ML methods, particularly at low LAI level in which the SVIs were adversely affected. Nevertheless, all the SVIs, except for the RVSI, performed moderately well at high and medium LAI levels. [ABSTRACT FROM AUTHOR]

Abstract Leaf rust, caused by Puccinia triticina (Pt), is one of the most important wheat diseases of common wheat (Triticum aestivum L.). Using resistant cultivars is the most economical and efficient way to control the disease. A total of 86 wheat cultivars from Sichuan province in China were inoculated with 14 Pt races for postulating seedling leaf rust resistance (Lr) gene(s) in the greenhouse. Meanwhile, these cultivars were also planted in Baoding and Zhoukou trial fields for identifying slow leaf rusting genes during the 2014–2015 and 2015–2016 cropping seasons. Twelve specific markers for ten known Lr genes (Lr1 , Lr9 , Lr10 , Lr19 , Lr20 , Lr24 , Lr26 , Lr34 , Lr37 and Lr46) were also used for molecular marker detection. Based on the results from the gene postulation and molecular marker detection, nine Lr genes (Lr1 , Lr2a, Lr26 , Lr3ka , Lr30 , Lr36 , Lr15 , Lr37 , and Lr46) were identified in 45 cultivars either singly or in combination. Most frequently identified Lr genes were Lr26 in 25 cultivars and Lr37 in 21 cultivars. Less frequently detected genes were Lr1 and Lr46 each in nine cultivars, Lr3ka in five cultivars, Lr30 in three cultivars and Lr36 in two cultivars. Lr2a and Lr15 were found in Chuannong 16 and Chuanmai 1, respectively. Twenty-nine cultivars were found to have slow rusting resistance during the two growing seasons. The results should be useful for selecting cultivars with combinations of genes for effective resistance to grow and in breeding new cultivars with improved resistance to leaf rust. [ABSTRACT FROM AUTHOR]

The wheat (Triticum aestivum L.) line 19HRWSN-129 from CIMMYT showed resistance to the major Puccinia triticina (Pt) races collected in China. A 144 F2:3 population was generated by crossing the resistant line 19HRWSN-129 with the susceptible line Zhengzhou5389. All the F2:3 plants were phenotyped by inoculating with the Pt race PHGN in the greenhouse. Segregation analysis indicated the presence of a single dominant gene conferring resistance to leaf rust in the wheat line 19HRWSN-129, temporarily designated as Lrshi. Using molecular markers, we mapped this resistance locus on chromosome 7BL. It was closely linked to the SSR markers Xgwm344 and Xcfa2040 with genetic distances of 2.8 cM and 1.4 cM, respectively. Compared with other chromosome 7BL-located leaf rust resistance genes (Lr14a, Lr14b, Lr68), we demonstrate, that Lrshi is a novel wheat leaf rust resistance gene.

Wheat leaf rust (caused by Puccinia triticina) is one of the most important fungal diseases in China. There are tens of winter wheat cultivars which are approved to be released by the government at a national level and more than 100 wheat cultivars at the provincial level. But there is no information about leaf rust (Lr) genes in these cultivars, which makes it difficult for farmers and breeders to select which cultivars they should plant in their fields and use in their breeding programs. The objective of this paper was to identify the leaf rust resistant genes at seedling stage present in the 84 commercial wheat cultivars from China that have been released in the past few years. A set of 20 near isogenic lines with Thatcher background and 6 lines with known Lr genes were used to test the virulence of 12 races of P. triticina (Pt). By comparing the infection types (ITs) produced on the 84 cultivars by the 12 Pt races with the ITs on the differential sets, the Lr genes were postulated. In addition, 8 molecular markers of Lr genes such as Lr9, Lr10, Lr19, Lr20, Lr21, Lr24, Lr26 and Lr29, which are closely linked to or co-segregated with the Lr gene, were used for further validation of the genes in the 84 Chinese winter wheat cultivars. Twelve Lr genes, including Lr1, Lr3, (Lr3bg), (Lr3ka), Lr11, Lr13, Lr14a, Lr16, Lr26, Lr27, Lr30 and Lr31 were postulated to be present either singly or in combinations in these Chinese wheat cultivars. Lr3 and Lr26 were detected most often in the tested cultivars, with frequencies of 51.2 and 38.1%, respectively. No wheat Lr genes were detected in 16 cultivars, and 4 cultivars may carry unknown Lr genes other than those used in this study. Lr9, Lr20, Lr21, Lr24, Lr25 and Lr29 were not present in any of the 84 tested accessions.