Resurgence of wheat stem rust infections in western Europe: causes and how to curtail them.

Ten years ago, (black) stem rust - the most damaging of wheat (Triticum aestivum) rusts - re-emerged in western Europe. Disease incidences have since increased in scale and frequency. Here, we investigated the likely underlying causes and used those to propose urgently needed mitigating actions. We report that the first large-scale UK outbreak of the wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), in 2022 may have been caused by timely arrival of airborne urediniospores from southwest Europe. The drive towards later-maturing wheat varieties in the UK may be exacerbating Pgt incidences, which could have disastrous consequences. Indeed, infection assays showed that two UK Pgt isolates from 2022 could infect over 96% of current UK wheat varieties. We determined that the temperature response data in current disease risk simulation models are outdated. Analysis of germination rates for three current UK Pgt isolates showed substantial variation in temperature response functions, suggesting that the accuracy of disease risk simulations would be substantially enhanced by incorporating data from prevailing Pgt isolates. As Pgt incidences continue to accelerate in western Europe, we advocate for urgent action to curtail Pgt losses and help safeguard future wheat production across the region.

Genome-wide association study identifies novel loci and candidate genes for rust resistance in wheat (Triticum aestivum L.).

BACKGROUND: Wheat rusts are important biotic stresses, development of rust resistant cultivars through molecular approaches is both economical and sustainable. Extensive phenotyping of large mapping populations under diverse production conditions and high-density genotyping would be the ideal strategy to identify major genomic regions for rust resistance in wheat. The genome-wide association study (GWAS) population of 280 genotypes was genotyped using a 35 K Axiom single nucleotide polymorphism (SNP) array and phenotyped at eight, 10, and, 10 environments, respectively for stem/black rust (SR), stripe/yellow rust (YR), and leaf/brown rust (LR). RESULTS: Forty-one Bonferroni corrected marker-trait associations (MTAs) were identified, including 17 for SR and 24 for YR. Ten stable MTAs and their best combinations were also identified. For YR, AX-94990952 on 1A + AX-95203560 on 4A + AX-94723806 on 3D + AX-95172478 on 1A showed the best combination with an average co-efficient of infection (ACI) score of 1.36. Similarly, for SR, AX-94883961 on 7B + AX-94843704 on 1B and AX-94883961 on 7B + AX-94580041 on 3D + AX-94843704 on 1B showed the best combination with an ACI score of around 9.0. The genotype PBW827 have the best MTA combinations for both YR and SR resistance. In silico study identifies key prospective candidate genes that are located within MTA regions. Further, the expression analysis revealed that 18 transcripts were upregulated to the tune of more than 1.5 folds including 19.36 folds (TraesCS3D02G519600) and 7.23 folds (TraesCS2D02G038900) under stress conditions compared to the control conditions. Furthermore, highly expressed genes in silico under stress conditions were analyzed to find out the potential links to the rust phenotype, and all four genes were found to be associated with the rust phenotype. CONCLUSION: The identified novel MTAs, particularly stable and highly expressed MTAs are valuable for further validation and subsequent application in wheat rust resistance breeding. The genotypes with favorable MTA combinations can be used as prospective donors to develop elite cultivars with YR and SR resistance.

Identification of candidate genes for adult plant stripe rust resistance transferred from Aegilops ventricosa 2NvS into wheat via fine mapping and transcriptome analysis.

KEY MESSAGE: An adult plant gene for resistance to stripe rust was narrowed down to the proximal one-third of the 2NvS segment translocated from Aegilops ventricosa to wheat chromosome arm 2AS, and based on the gene expression analysis, two candidate genes were identified showing a stronger response at the adult plant stage compared to the seedling stage. The 2NvS translocation from Aegilops ventricosa, known for its resistance to various diseases, has been pivotal in global wheat breeding for more than three decades. Here, we identified an adult plant resistance (APR) gene in the 2NvS segment in wheat line K13-868. Through fine mapping in a segregating near-isogenic line (NIL) derived population of 6389 plants, the candidate region for the APR gene was narrowed down to between 19.36 Mb and 33 Mb in the Jagger reference genome. Transcriptome analysis in NILs strongly suggested that this APR gene conferred resistance to stripe rust by triggering plant innate immune responses. Based on the gene expression analysis, two disease resistance-associated genes within the candidate region, TraesJAG2A03G00588940 and TraesJAG2A03G00590140, exhibited a stronger response to Puccinia striiformis f. sp. tritici (Pst) infection at the adult plant stage than at the seedling stage, indicating that they could be potential candidates for the resistance gene. Additionally, we developed a co-dominant InDel marker, InDel_31.05, for detecting this APR gene. Applying this marker showed that over one-half of the wheat varieties approved in 2021 and 2022 in Sichuan province, China, carry this gene. Agronomic trait evaluation of NILs indicated that the 2NvS segment effectively mitigated the negative effects of stripe rust on yield without affecting other important agronomic traits. This study provided valuable insights for cloning and breeding through the utilization of the APR gene present in the 2NvS segment.

Integrated genome-wide association and transcriptomic analysis to identify receptor kinase genes to stripe rust resistance in wheat germplasm from southwestern China.

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat worldwide. Identification of new and elite Pst-resistance loci or genes has the potential to enhance overall resistance to this pathogen. Here, we conducted an integrated genome-wide association study (GWAS) and transcriptomic analysis to screen for loci associated with resistance to stripe rust in 335 accessions from Yunnan, including 311 landraces and 24 cultivars. Based on the environmental phenotype, we identified 113 protein kinases significantly associated with Pst resistance using mixed linear model (MLM) and generalized linear model (GLM) models. Transcriptomic analysis revealed that 52 of 113 protein kinases identified by GWAS were up and down regulated in response to Pst infection. Among these genes, a total of 15 receptor kinase genes were identified associated with Pst resistance. 11 candidate genes were newly discovered in Yunnan wheat germplasm. Our results revealed that resistance alleles to stripe rust were accumulated in Yunnan wheat germplasm, implying direct or indirect selection for improving stripe rust resistance in elite wheat breeding programs.

Mapping and characterization of rust resistance genes Lr53 and Yr35 introgressed from Aegilops species.

KEY MESSAGE: The rust resistance genes Lr53 and Yr35 were introgressed into bread wheat from Aegilops longissima or Aegilops sharonensis or their S-genome containing species and mapped to the telomeric region of chromosome arm 6BS. Wheat leaf and stripe rusts are damaging fungal diseases of wheat worldwide. Breeding for resistance is a sustainable approach to control these two foliar diseases. In this study, we used SNP analysis, sequence comparisons, and cytogenetic assays to determine that the chromosomal segment carrying Lr53 and Yr35 was originated from Ae.longissima or Ae. sharonensis or their derived species. In seedling tests, Lr53 conferred strong resistance against all five Chinese Pt races tested, and Yr35 showed effectiveness against Pst race CYR34 but susceptibility to race CYR32. Using a large population (3892 recombinant gametes) derived from plants homozygous for the ph1b mutation obtained from the cross 98M71 × CSph1b, both Lr53 and Yr35 were successfully mapped to a 6.03-Mb telomeric region of chromosome arm 6BS in the Chinese Spring reference genome v1.1. Co-segregation between Lr53 and Yr35 was observed within this large mapping population. Within the candidate region, several nucleotide-binding leucine-rich repeat genes and protein kinases were identified as candidate genes. Marker pku6B3127 was completely linked to both genes and accurately predicted the absence or presence of alien segment harboring Lr53 and Yr35 in 87 tetraploid and 149 hexaploid wheat genotypes tested. We developed a line with a smaller alien segment (< 6.03 Mb) to reduce any potential linkage drag and demonstrated that it conferred resistance levels similar to those of the original donor parent 98M71. The newly developed introgression line and closely linked PCR markers will accelerate the deployment of Lr53 and Yr35 in wheat breeding programs.

Stripe rust effector Pst03724 modulates host immunity by inhibiting NAD kinase activation by a calmodulin.

Puccinia striiformis f. sp. tritici (Pst) secretes effector proteins that enter plant cells to manipulate host immune processes. In this report, we present an important Pst effector, Pst03724, whose mRNA expression level increases during Pst infection of wheat (Triticum aestivum). Silencing of Pst03724 reduced the growth and development of Pst. Pst03724 targeted the wheat calmodulin TaCaM3-2B, a positive regulator of wheat immunity. Subsequent investigations revealed that Pst03724 interferes with the TaCaM3-2B-NAD kinase (NADK) TaNADK2 association and thus inhibits the enzyme activity of TaNADK2 activated by TaCaM3-2B. Knocking down TaNADK2 expression by virus-mediated gene silencing significantly increased fungal growth and development, suggesting a decrease in resistance against Pst infection. In conclusion, our findings indicate that Pst effector Pst03724 inhibits the activity of NADK by interfering with the TaCaM3-2B-TaNADK2 association, thereby facilitating Pst infection.

Dynamics of Puccinia striiformis f. sp. tritici Urediniospores and Its Relationship with Meteorological Factors in Mianyang, China.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the main diseases of wheat worldwide. Mianyang of Sichuan province in Southwest China is one of main regions for winter Pst inoculum production and spring epidemic and provides urediniospores for infecting wheat in the surrounding regions. Understanding the urediniospore dynamics is important to predict and manage stripe rust. In this study, spore trapping coupled with a TaqMan real-time quantitative PCR method was used to monitor airborne Pst urediniospores from December 2019 to December 2022 in Mianyang. Weather conditions (temperature, relative humidity, daily sunshine duration, and precipitation) were collected for the same period. These data were used to study the relationship of airborne urediniospore density with climatic conditions. The results showed that Pst urediniospores were captured all year round, and the annual peak of urediniospore densities occurred in the period from March to April in which the urediniospores accounted for the largest proportion of the annual total urediniospores. The density of urediniospores in the period of March to April was linearly related to the average sunshine duration of 20 days and average temperature of 15 days prior to the final day of a 7-day trapping period. This relationship needs to be tested in other regions where Pst can sporulate during the winter before it can be integrated with Pst infection conditions to predict rust development.

CRISPR-targeted mutagenesis of mitogen-activated protein kinase phosphatase 1 improves both immunity and yield in wheat.

Plants have evolved a sophisticated immunity system for specific detection of pathogens and rapid induction of measured defences. Over- or constitutive activation of defences would negatively affect plant growth and development. Hence, the plant immune system is under tight positive and negative regulation. MAP kinase phosphatase1 (MKP1) has been identified as a negative regulator of plant immunity in model plant Arabidopsis. However, the molecular mechanisms by which MKP1 regulates immune signalling in wheat (Triticum aestivum) are poorly understood. In this study, we investigated the role of TaMKP1 in wheat defence against two devastating fungal pathogens and determined its subcellular localization. We demonstrated that knock-down of TaMKP1 by CRISPR/Cas9 in wheat resulted in enhanced resistance to rust caused by Puccinia striiformis f. sp. tritici (Pst) and powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt), indicating that TaMKP1 negatively regulates disease resistance in wheat. Unexpectedly, while Tamkp1 mutant plants showed increased resistance to the two tested fungal pathogens they also had higher yield compared with wild-type control plants without infection. Our results suggested that TaMKP1 interacts directly with dephosphorylated and activated TaMPK3/4/6, and TaMPK4 interacts directly with TaPAL. Taken together, we demonstrated TaMKP1 exert negative modulating roles in the activation of TaMPK3/4/6, which are required for MAPK-mediated defence signalling. This facilitates our understanding of the important roles of MAP kinase phosphatases and MAPK cascades in plant immunity and production, and provides germplasm resources for breeding for high resistance and high yield.

Characterization of Quantitative Trait Loci for Leaf Rust Resistance in the Uzbekistani Wheat Landrace Teremai Bugdai.

Leaf rust, caused by Puccinia triticina, is a major cause of wheat yield losses globally, and novel leaf rust resistance genes are needed to enhance wheat leaf rust resistance. Teremai Bugdai is a landrace from Uzebekistan that is highly resistant to many races of P. triticina in the United States. To unravel leaf rust resistance loci in Teremai Bugdai, a recombinant inbred line (RIL) population of Teremai Bugdai × TAM 110 was evaluated for response to P. triticina race Pt54-1 (TNBGJ) and genotyped using single nucleotide polymorphism (SNP) markers generated by genotyping-by-sequencing (GBS). Quantitative trait loci (QTL) analysis using 5,130 high-quality GBS-SNPs revealed three QTLs, QLr-Stars-2DS, QLr-Stars-6BL, and QLr.Stars-7BL, for leaf rust resistance in two experiments. QLr-Stars-2DS, which is either a new Lr2 allele or a new resistance locus, was delimited to an ∼19.47-Mb interval between 46.4 and 65.9 Mb on 2DS and explained 31.3 and 33.2% of the phenotypic variance in the two experiments. QLr-Stars-6BL was mapped in an ∼84.0-kb interval between 719.48 and 719.56 Mb on 6BL, accounting for 33 to 36.8% of the phenotypic variance in two experiments. QLr.Stars-7BL was placed in a 350-kb interval between 762.41 and 762.76 Mb on 7BL and explained 4.4 to 5.3% of the phenotypic variance. Nine GBS-SNPs flanking these QTLs were converted to kompetitive allele specific PCR (KASP) markers, and these markers can be used to facilitate their introgression into locally adapted wheat lines.

Application of a U-Net Neural Network to the Puccinia sorghi-Maize Pathosystem.

Computer vision approaches to analyze plant disease data can be both faster and more reliable than traditional, manual methods. However, the requirement of manually annotating training data for the majority of machine learning applications can present a challenge for pipeline development. Here, we describe a machine learning approach to quantify Puccinia sorghi incidence on maize leaves utilizing U-Net convolutional neural network models. We analyzed several U-Net models with increasing amounts of training image data, either randomly chosen from a large data pool or randomly chosen from a subset of disease time course data. As the training dataset size increases, the models perform better, but the rate of performance decreases. Additionally, the use of a diverse training dataset can improve model performance and reduce the amount of annotated training data required for satisfactory performance. Models with as few as 48 whole-leaf training images are able to replicate the ground truth results within our testing dataset. The final model utilizing our entire training dataset performs similarly to our ground truth data, with an intersection over union value of 0.5002 and an F1 score of 0.6669. This work illustrates the capacity of U-Nets to accurately answer real-world plant pathology questions related to quantification and estimation of plant disease symptoms. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Enhanced stripe rust resistance obtained by combining Yr30 with a widely dispersed, consistent QTL on chromosome arm 4BL.

KEY MESSAGE: YrFDC12 and PbcFDC, co-segregated in chromosome 4BL, and significantly interacted with Yr30/Pbc1 to enhance stripe rust resistance and to promote pseudo-black chaff development. Cultivars with durable resistance are the most popular means to control wheat stripe rust. Durable resistance can be achieved by stacking multiple adult plant resistance (APR) genes that individually have relatively small effect. Chinese wheat cultivars Ruihua 520 (RH520) and Fengdecun 12 (FDC12) confer partial APR to stripe rust across environments. One hundred and seventy recombinant inbred lines from the cross RH520 × FDC12 were used to determine the genetic basis of resistance and identify genomic regions associated with stripe rust resistance. Genotyping was carried out using 55 K SNP array, and eight quantitative trait loci (QTL) were detected on chromosome arms 2AL, 2DS, 3BS, 4BL, 5BL (2), and 7BL (2) by inclusive composite interval mapping. Only QYr.nwafu-3BS from RH520 and QYr.nwafu-4BL.2 (named YrFDC12 for convenience) from FDC12 were consistent across the four testing environments. QYr.nwafu-3BS is likely the pleiotropic resistance gene Sr2/Yr30. YrFDC12 was mapped in a 2.1-cM interval corresponding to 12 Mb and flanked by SNP markers AX-111121224 and AX-89518393. Lines harboring both Yr30 and YrFDC12 displayed higher resistance than the parents and expressed pseudo-black chaff (PBC) controlled by loci Pbc1 and PbcFDC12, which co-segregated with Yr30 and YrFDC12, respectively. Both marker-based and pedigree-based kinship analyses revealed that YrFDC12 was inherited from founder parent Zhou 8425B. Fifty-four other wheat cultivars shared the YrFDC12 haplotype. These results suggest an effective pyramiding strategy to acquire highly effective, durable stripe rust resistance in breeding.

Wheat genetic loci conferring resistance to stripe rust in the face of genetically diverse races of the fungus Puccinia striiformis f. sp. tritici.

KEY MESSAGE: Analysis of a wheat multi-founder population identified 14 yellow rust resistance QTL. For three of the four most significant QTL, haplotype analysis indicated resistance alleles were rare in European wheat. Stripe rust, or yellow rust (YR), is a major fungal disease of wheat (Triticum aestivum) caused by Puccinia striiformis Westend f. sp. tritici (Pst). Since 2011, the historically clonal European Pst races have been superseded by the rapid incursion of genetically diverse lineages, reducing the resistance of varieties previously showing durable resistance. Identification of sources of genetic resistance to such races is a high priority for wheat breeding. Here we use a wheat eight-founder multi-parent population genotyped with a 90,000 feature single nucleotide polymorphism array to genetically map YR resistance to such new Pst races. Genetic analysis of five field trials at three UK sites identified 14 quantitative trait loci (QTL) conferring resistance. Of these, four highly significant loci were consistently identified across all test environments, located on chromosomes 1A (QYr.niab-1A.1), 2A (QYr.niab-2A.1), 2B (QYr.niab-2B.1) and 2D (QYr.niab-2D.1), together explaining ~ 50% of the phenotypic variation. Analysis of these four QTL in two-way and three-way combinations showed combinations conferred greater resistance than single QTL, and genetic markers were developed that distinguished resistant and susceptible alleles. Haplotype analysis in a collection of wheat varieties found that the haplotypes associated with YR resistance at three of these four major loci were rare (≤ 7%) in European wheat, highlighting their potential utility for future targeted improvement of disease resistance. Notably, the physical interval for QTL QYr.niab-2B.1 contained five nucleotide-binding leucine-rich repeat candidate genes with integrated BED domains, of which two corresponded to the cloned resistance genes Yr7 and Yr5/YrSp.

Aeciospore ejection in the rust pathogen Puccinia graminis is driven by moisture ingress.

Fungi have evolved an array of spore discharge and dispersal processes. Here, we developed a theoretical model that explains the ejection mechanics of aeciospore liberation in the stem rust pathogen Puccinia graminis. Aeciospores are released from cluster cups formed on its Berberis host, spreading early-season inoculum into neighboring small-grain crops. Our model illustrates that during dew or rainfall, changes in aeciospore turgidity exerts substantial force on neighboring aeciospores in cluster cups whilst gaps between spores become perfused with water. This perfusion coats aeciospores with a lubrication film that facilitates expulsion, with single aeciospores reaching speeds of 0.053 to 0.754 m·s-1. We also used aeciospore source strength estimates to simulate the aeciospore dispersal gradient and incorporated this into a publicly available web interface. This aids farmers and legislators to assess current local risk of dispersal and facilitates development of sophisticated epidemiological models to potentially curtail stem rust epidemics originating on Berberis.

The RLK protein TaCRK10 activates wheat high-temperature seedling-plant resistance to stripe rust through interacting with TaH2A.1.

Plants sense various pathogens and activate immunity responses through receptor-like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6) that harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knockdown of TaCRK10 by virus-induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, whereas there is no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance only under normal temperatures at 14 days with reactive oxygen species accumulation and defense-related gene expression of the salicylic acid pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.

Distribution, dynamics, and physiological races of wheat stem rust (Puccinia graminis f.sp. tritici) on irrigated wheat in the Awash River Basin of Ethiopia.

Wheat is one of the high-value major crops in the world. However, wheat stem rust is considered one of the determinant threats to wheat production in Ethiopia and the world. So this study was conducted to assess the disease intensity, seasonal distribution dynamics pattern, the genetic variability of Puccinia graminis f. sp. tritici, and to determine the virulence spectrum in the irrigated ecology of the Awash River Basin. Totally 137 wheat farms were evaluated, from 2014/15-2019/20 in six districts representing the Upper, Middle, and Lower Awash River Basin. Farm plots were assessed, in every 5-10 km intervals, with 'X' fashion, and data on disease incidence, severity, healthy plants were counted and recorded. Diseased samples were collected from the diseased wheat stem by Puccinia graminis physiological and genetic race analysis. The seasonal trend of stem rust disease progress showed its importance to infer the future progresses of the disease for the country's potential production plan of irrigated wheat. The result revealed that the disease prevalence, disease incidence, and severity were significantly varied; among the different districts and seasons in the two regions. The survey results also indicated that about 71.7% of the wheat fields were affected by stem rust during the 2018/19 growing period. The disease's overall incidence and mean severity during the same season were 49.02% and 29.27%, respectively. In 2019/20, about 63.7% of the wheat fields were affected by stem rust, disease incidence 30.97%, and severity 17.22% were lower than the previous season. In 2019/20, even though seasonal disease distribution decreased, the spatial distribution was expanding in Afambo and Dubti districts. Four, stem rust dominant races were identified (TTTTF, TKTTF TKKTF, and TTKTF) by physiological and genetic race analysis during 2018/19 and one additional race (TKPTF) in 2019/20, production year. The result indicated that the races are highly virulent and affect most Sr genes except Sr31 and Sr24. From the race analysis result, TTTTF, and TKKTF have the broadest virulence spectrum race, which affects 90% of the Sr genes. Generally, we can conclude that the spatial and seasonal distribution of the disease is expanding. Most of the races in the irrigated areas in the Basin were similar to that of rain-fed wheat production belts in Ethiopia, so care must be given, to effective management of the diseases, in both production ecologies towards controlling the spore pressure than race variability. Therefore, these findings provide inputs for wheat producers to reduce the spread and disease' damage in the irrigated ecologies of Ethiopia. Also, it gives an insight for breeders to think about the breeding program in their crossing lines.

A random forest model for the classification of wheat and rye leaf rust symptoms based on pure spectra at leaf scale.

The pure spectra acquisition of plant disease symptoms is essential to improving the reliability of remote sensing methods in crop protection. The reflectance values read from the pure spectra can be used as valuable training data for development of algorithms designed for plant disease detection at leaf and canopy scale. The aim of this paper is to identify and distinguish spectrally the leaf rust symptoms caused by two closely related special forms (f. sp.) of Puccinia recondita f. sp. tritici on wheat and Puccinia recondita f. sp. recondita on rye at leaf scale. Spectral measurements were made with FieldSpec 3 spectrometer in the wavelength range of 350-2500 nm. The spectrometer was connected to a microscope by optical fiber. Raw spectra of uredinia, chlorotic discoloration, green leaves, senescent inoculated leaves and senescent uninoculated leaves of wheat and rye, all of which obtained for this study, were investigated with a view towards making an automized classification of plant species and their phases. The created Random Forest models were tested separately using pure spectra, and from these vegetation indices were derived as predictors. Three vegetation indices, namely CRI, PRI and GNDVI, appeared to be the most robust in terms of distinguishing uredinia from other symptoms on rye and wheat leaves. PRI, EVI, NDVI705, and GNDVI were the most suitable for distinguishing uredinia, chlorotic discoloration, and green leaf stages on rye. That tusk on wheat leaves can be recognized if seven indices (PRI, MSAWI, SAVI, NDVI, NDVI705, GNDVI and RVI) are used together. For the classification of all disease symptoms for both plant species, the most useful were wavelengths in the VIS range: 431-436, 696-703 and 646-686 nm. However, the ranges of SWIR wavelengths (1938, 1955) and NIR wavelengths (1099-1104) also have a high contribution to the discrimination accuracy of the model. In the classification of all disease symptoms, the most important vegetation indices were CRI, OSAVI, and GNDVI. Analysis of the results revealed the advantage of the model based on the selected spectral wavelengths (Hit Rate of 96.6%) in comparison with predictions based on vegetation indices alone (Hit Rate of 91.7%). Both approaches show the highly applicable character of utilizing high quality spectral products such as satellite images in reducing operational costs of crop protection.

Battling the biotypes of balsam: the biological control of Impatiens glandulifera using the rust fungus Puccinia komarovii var. glanduliferae in GB.

Impatiens glandulifera, or Himalayan balsam, is a prolific invader of riverine habitats. Introduced from the Himalayas for ornamental purposes in 1839, this annual species has naturalised across Great Britain (GB) forming dense monocultures with negative affects across whole ecosystems. In 2006 a programme exploring biocontrol as an alternative control method was initiated and to date, two strains of the rust fungus Puccinia komarovii var. glanduliferae have been released. To better understand the observed differences in susceptibility of GB Himalayan balsam stands to the two rust strains, inoculation studies were conducted using urediniospores and basidiospores. Experiments revealed large variation in the susceptibility of stands to urediniospores of the two rust strains, with some resistant to both. Furthermore, the infectivity of basidiospores was found to differ, with some stands fully susceptible to the urediniospore stage, being immune to basidiospore infection. Therefore, before further rust releases at new sites, it is necessary to ensure complete compatibility of the invasive stands with both urediniospores and basidiospores. However, for successful control across GB it is essential that plant biotypes are matched to the most virulent rust strains. This will involve additional strains from the native range to tackle those biotypes resistant to the strains currently released.

Effectors of Puccinia striiformis f. sp. tritici Suppressing the Pathogenic-Associated Molecular Pattern-Triggered Immune Response Were Screened by Transient Expression of Wheat Protoplasts.

Puccinia striiformis f. sp. tritici (Pst) is an important pathogen of wheat (Triticum aestivum L.) stripe rust, and the effector protein secreted by haustoria is a very important component involved in the pathogenic process. Although the candidate effector proteins secreted by Pst haustoria have been predicted to be abundant, few have been functionally validated. Our study confirmed that chitin and flg22 could be used as elicitors of the pathogenic-associated molecular pattern-triggered immune (PTI) reaction in wheat leaves and that TaPr-1-14 could be used as a marker gene to detect the PTI reaction. In addition, the experimental results were consistent in wheat protoplasts. A rapid and efficient method for screening and identifying the effector proteins of Pst was established by using the wheat protoplast transient expression system. Thirty-nine Pst haustorial effector genes were successfully cloned and screened for expression in the protoplast. We identified three haustorial effector proteins, PSEC2, PSEC17, and PSEC45, that may inhibit the response of wheat to PTI. These proteins are localized in the somatic cytoplasm and nucleus of wheat protoplasts and are highly expressed during the infection and parasitism of wheat.

The small GTP-binding protein TaRop10 interacts with TaTrxh9 and functions as a negative regulator of wheat resistance against the stripe rust.

Small GTP-binding proteins, also known as ROPs (Rho of Plants), are a subfamily of the Ras superfamily of signaling G-proteins and are required for numerous signaling processes, ranging from growth and development to biotic and abiotic signaling. In this study, we cloned and characterized wheat TaRop10, a homolog of Arabidopsis ROP10 and member of the class II ROP, and uncovered a role for TaRop10 in wheat response to Puccinia striiformis f. sp. tritici (Pst). TaRop10 was downregulated by actin depolymerization and was observed to be differentially induced by abiotic stress and the perception of plant hormones. A combination of yeast two-hybrid and bimolecular fluorescence complementation assays revealed that TaRop10 interacted with a h-type thioredoxin (TaTrxh9). Knocking-down of TaRop10 and TaTrxh9 was performed using the BSMV-VIGS (barley stripe mosaic virus-based virus-induced gene silencing) technique and revealed that TaRop10 and TaTrxh9 play a role in the negative regulation of defense signaling in response to Pst infection. In total, the data presented herein further illuminate our understanding of how intact plant cells accommodate fungal infection structures, and furthermore, support the function of TaRop10 and TaTrxh9 in negative modulation of defense signaling in response to stripe rust infection.

TaAP2-15, An AP2/ERF Transcription Factor, Is Positively Involved in Wheat Resistance to Puccinia striiformis f. sp. tritici.

AP2 transcription factors play a crucial role in plant development and reproductive growth, as well as response to biotic and abiotic stress. However, the role of TaAP2-15, in the interaction between wheat and the stripe fungus, Puccinia striiformis f. sp. tritici (Pst), remains elusive. In this study, we isolated TaAP2-15 and characterized its function during the interaction. TaAP2-15 was localized in the nucleus of wheat and N. benthamiana. Silencing of TaAP2-15 by barley stripe mosaic virus (BSMV)-mediated VIGS (virus-induced gene silencing) increased the susceptibility of wheat to Pst accompanied by enhanced growth of the pathogen (number of haustoria, haustorial mother cells and hyphal length). We confirmed by quantitative real-time PCR that the transcript levels of pathogenesis-related genes (TaPR1 and TaPR2) were down-regulated, while reactive oxygen species (ROS)-scavenging genes (TaCAT3 and TaFSOD3D) were induced accompanied by reduced accumulation of H2O2. Furthermore, we found that TaAP2-15 interacted with a zinc finger protein (TaRZFP34) that is a homolog of OsRZFP34 in rice. Together our findings demonstrate that TaAP2-15 is positively involved in resistance of wheat to the stripe rust fungus and provides new insights into the roles of AP2 in the host-pathogen interaction.