Resistant Wheat Cultivars Research Articles

Diallel Analysis of Wheat Resistance to Fusarium Head Blight and Mycotoxin Accumulation under Conditions of Artificial Inoculation and Natural Infection.

Breeding resistant wheat cultivars to Fusarium head blight (FHB), caused by Fusarium spp., is the best method for controlling the disease. The aim of this study was to estimate general combining ability (GCA) and specific combining ability (SCA) for FHB resistance in a set of eight genetically diverse winter wheat cultivars to identify potential donors of FHB resistance for crossing. FHB resistance of parents and F1 crosses produced by the half diallel scheme was evaluated under the conditions of artificial inoculation with F. graminearum and natural infection. Four FHB related traits were assessed: visual rating index (VRI), Fusarium damaged kernels (FDK), and deoxynivalenol and zearalenone content in the harvested grain samples. Significant GCA effects for FHB resistance were observed for the parental cultivars with high FHB resistance for all studied FHB resistance related traits. The significant SCA and mid-parent heterosis effects for FHB resistance were rare under both artificial inoculation and natural infection conditions and involved crosses between parents with low FHB resistance. A significant negative correlation between grain yield under natural conditions and VRI (r = -0.43) and FDK (r = -0.47) under conditions of artificial inoculation was observed in the set of the studied F1 crosses. Some crosses showed high yield and high FHB resistance, indicating that breeding of FHB resistant genotypes could be performed without yield penalty. These crosses involved resistant cultivars with significant GCA effects for FHB resistance indicating that that they could be used as good donors of FHB resistance.

QTL Mapping of Adult Plant Resistance to Powdery Mildew in Chinese Wheat Landrace Baidatou.

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases affecting wheat throughout the world. Breeding and growing resistant wheat cultivars is one of the most economic and effective methods to control the disease, and as such, identifying and mapping the new and effective resistance genes is critical. Baidatou, a Chinese wheat landrace, shows excellent field resistance to powdery mildew. To identify the resistance gene(s) in Baidatou, 170 F7:8 recombinant inbred lines (RILs) derived from the cross Mingxian 169/Baidatou were evaluated for powdery mildew response at the adult-plant stage in the experimental fields in Yangling (YL) of Shaanxi Province and Tianshui (TS) in Gansu Province in 2019, 2020, and 2021. The relative area under disease progress curve (rAUDPC) of Mingxian 169/Baidatou F7:8 RILs indicated that the resistance of Baidatou to powdery mildew was controlled by quantitative trait loci (QTLs). Based on bulk segregation analysis combined with the 660K single nucleotide polymorphism (SNP) array and genotyping by target sequencing (16K SNP) of the entire RIL population, two QTLs, QPmbdt.nwafu-2AS and QPmbdt.nwafu-3AS, were identified, and these accounted for up to 44.5% of the phenotypic variation. One of the QTLs was located on the 3.32 cM genetic interval on wheat chromosome 2AS between the kompetitive allele-specific PCR markers AX-111012288 and AX_174233809, and another was located on the 9.6 cM genetic interval on chromosome 3AS between the SNP markers 3A_684044820 and 3A_686681822. These markers could be useful for successful breeding of powdery mildew resistance in wheat.

Tetraploid wheat (Triticum turgidum) lines from the United States as a source of Hessian fly (Mayetiola destructor) resistance

AbstractDeploying resistant wheat cultivars is the most economical and environment‐friendly strategy to manage the devastating effects of the dipteran pest, Hessian fly (Hf; Mayetiola destructor). Currently, 37 Hf resistance genes have been identified to combat the 18 Hf genotypes documented so far. However, the Hf populations adapt rapidly to overcome the newly deployed resistance genes within a few years of release resulting in development of virulent Hf biotypes and breakdown of plant resistance. Identification of new and novel sources of resistance offers breeders additional resources that can be included in the breeding programmes to develop elite Hf‐resistant cultivars. In the current study, we screened 374 wheat (tetraploid and hexaploid) accessions originating from different regions of the United States and identified three tetraploid (Triticum turgidum) pasta wheat lines, one originating from North Dakota (PI 639869) and two from Minnesota (PI 352398 and CItr 15710) exhibiting ≥95% resistance to Hf biotype L at 20°C. Further, the wheat cultivar PI 352398 showed 100% resistance to six additional Hf genotypes including biotypes B, C, D, O, GP and vH13. The lines PI 639869 and CItr 15710 also showed >70% resistance with most biotypes, except against biotype GP with the former and biotype B with the latter. Interestingly, a few plants from these two cultivars exhibited putative tolerance to these biotypes where the plants showed normal growth but harboured white, live larvae and showed cell permeability that was intermediate in levels between Hf‐infested resistant and susceptible wheat. Additionally, since the increase in environmental temperatures to 25–30°C also negatively impacts Hf resistance, the three T. turgidum (PI 639869, PI 352398 and CItr 15710) cultivars were evaluated for Hf resistance at 30°C. None of the wheat cultivars were resistant to Hf biotype L at 30°C indicating a temperature‐dependent breakdown of resistance and are therefore not suitable for geographical regions with higher environmental temperatures. Taken together, these three wheat lines represent additional sources of Hf resistance that can be leveraged by breeders for developing durable elite lines.

Genome-wide association study of common resistance to rust species in tetraploid wheat.

Rusts of the genus Puccinia are wheat pathogens. Stem (black; Sr), leaf (brown; Lr), and stripe (yellow; Yr) rust, caused by Puccinia graminis f. sp. tritici (Pgt), Puccinia triticina (Pt), and Puccinia striiformis f. sp. tritici (Pst), can occur singularly or in mixed infections and pose a threat to wheat production globally in terms of the wide dispersal of their urediniospores. The development of durable resistant cultivars is the most sustainable method for controlling them. Many resistance genes have been identified, characterized, genetically mapped, and cloned; several quantitative trait loci (QTLs) for resistance have also been described. However, few studies have considered resistance to all three rust pathogens in a given germplasm. A genome-wide association study (GWAS) was carried out to identify loci associated with resistance to the three rusts in a collection of 230 inbred lines of tetraploid wheat (128 of which were Triticum turgidum ssp. durum) genotyped with SNPs. The wheat panel was phenotyped in the field and subjected to growth chamber experiments across different countries (USA, Mexico, Morocco, Italy, and Spain); then, a mixed linear model (MLM) GWAS was performed. In total, 9, 34, and 5 QTLs were identified in the A and B genomes for resistance to Pgt, Pt, and Pst, respectively, at both the seedling and adult plant stages. Only one QTL on chromosome 4A was found to be effective against all three rusts at the seedling stage. Six QTLs conferring resistance to two rust species at the adult plant stage were mapped: three on chromosome 1B and one each on 5B, 7A, and 7B. Fifteen QTLs conferring seedling resistance to two rusts were mapped: five on chromosome 2B, three on 7B, two each on 5B and 6A, and one each on 1B, 2A, and 7A. Most of the QTLs identified were specific for a single rust species or race of a species. Candidate genes were identified within the confidence intervals of a QTL conferring resistance against at least two rust species by using the annotations of the durum (cv. 'Svevo') and wild emmer wheat ('Zavitan') reference genomes. The 22 identified loci conferring resistance to two or three rust species may be useful for breeding new and potentially durable resistant wheat cultivars.

QTL Mapping for Adult-Plant Resistance to Leaf Rust in Italian Wheat Cultivar Libellula.

Wheat leaf rust (Lr), which is caused by Puccinia triticina Eriks. (Pt), is one of the most important wheat diseases affecting wheat production globally. Using resistant wheat cultivars is the most economical and environmentally friendly way to control leaf rust. The Italian wheat cultivar Libellula has demonstrated good resistance to Lr in field studies. To identify the genetic basis of Lr resistance in 'Libellula', 248 F6 recombinant inbred lines from the cross 'Libellula'/'Huixianhong' was phenotyped for Lr severity in seven environments: the 2014/2015, 2016/2017, 2017/2018, and 2018/2019 cropping seasons at Baoding, Hebei Province, and the 2016/2017, 2017/2018, and 2018/2019 crop seasons at Zhoukou, Henan Province. Bulked segregant analysis and simple sequence repeat markers were then used to identify the quantitative trait loci (QTLs) for Lr adult-plant resistance in the population. Six QTLs were consequently detected and designated as QLr.hebau-1AL and QLr.hebau-1AS that were presumed to be new and QLr.hebau-1BL, QLr.hebau-3AL, QLr.hebau-4BL, and QLr.hebau-7DS that were identified at similar physical positions as previously reported QTLs. Based on chromosome positions and molecular marker tests, QLr.hebau-1BL and QLr.hebau-7DS share similar flanking markers with Lr46 and Lr34, respectively. Lr46 and Lr34 are race nonspecific adult plant resistance (APR) genes for leaf rust and stripe rust and powdery mildew. QLr.hebau-4BL showed multiple disease resistance to leaf rust, stripe rust, Fusarium head blight, and powdery mildew. The QTL identified in this study, as well as their closely linked markers, may potentially be used in marker-assisted selection in wheat breeding.

Physiological and molecular responses of a resistant and susceptible wheat cultivar to the fungal wheat pathogen Zymoseptoria tritici.

Zymoseptoria tritici is the causal agent of Septoria tritici blotch (STB), one of the most economically destructive wheat foliar diseases. In this study, we explore the physiological and molecular changes elicited in two wheat cultivars with divergent responses (Taichung 29 = susceptible, and Shafir = resistant) upon infection by Z. tritici. Our aim is to uncover novel insights into the intricate mechanisms that govern wheat defense against Z. tritici infection. Our quantitative histopathological study showed that H2O2 accumulated in the resistant cultivar to a higher degree compared to the susceptible cultivar at the biotrophic and switching phase. Additionally, we combined qPCR with a targeted quantitative HPLC technique to evaluate the expression profiles of 13 defense-related genes and profile the polyphenolic compounds induced differentially in the STB susceptible and resistant cultivar. Our finding indicated that five out of 13 genes were strongly up-regulated in the resistant cultivar compared with that of the susceptible one at eight days post-inoculation (dpi), corresponding to the transition phase present in the infection process of Z. tritici. Finally, our targeted HPLC analysis demonstrated that the traced phenolic compounds were highly elevated in the susceptible cultivar infected by Z. tritici compared with that of the resistant cultivar. In conclusion, our comprehensive analysis unveils a robust defense response in the resistant wheat cultivar Shafir, characterized by heightened H2O2 accumulation, significant up-regulation of key defense-related genes during the transition phase, and a distinct profile of polyphenolic compounds, shedding light on the intricate mechanisms contributing to its resistance against Z. tritici, thereby providing valuable insights for the development of more resilient wheat varieties.

Variation of Fusarium Head Blight Attack in Semidwarf Wheat Cultivars and Relationship with Stripe Rust Attack

Fusarium head blight (FHB) is a major threat to wheat production worldwide. We studied the Type 2 resistance of nineteen winter wheat cultivars under artificial inoculation by injecting spores of two Fusarium isolates into central florets of spikes. Weather conditions and Fusarium isolates used for artificial inoculations strongly influenced Fusarium attacks, but we also observed significant differences between cultivars. Six semidwarf wheat cultivars carrying Rht-B1b allele had significantly lower average Area Under Disease Progress Curve (AUDPC) than other cultivars, including two taller cultivars. Three of the six best resistant wheat cultivars carried the 1A-1R translocation, suggesting a beneficial effect of this rye chromatin presence on reducing the Fusarium head blight attack. Presence of stripe rust attacks significantly increased the area under disease development curve for Fusarium head blight, demonstrating the importance of debilitating effects of other biotic stresses.

Correlação entre resistência à brusone em cultivares de trigo e taxa de esporulação de conídios de Pyricularia oryzae Triticum

ABSTRACT: The use of resistant wheat cultivars is a fundamental strategy to minimize the damages caused by blast, a disease caused by the fungus Pyricularia oryzae Triticum (PoT). The objetive of this stydy was to (a) evaluate the reaction to blast of Brazilian wheat cultivars and (b) determine whether there is correlation between severity of symptoms on wheat spikes and “sporulation rate of PoT conidia per gram of wheat spike rachis” (Rscon). Plants of 16 wheat cultivars were grown in greenhouse until flowering (Zadoks stage 65), when their spikes were inoculated with a suspension formed by mixing the conidia of three PoT isolates. The evaluated variables were blast severity on spikes at 5, 7 and 11 days after inoculation (dai) and Rscon. Rachis were evaluated individually to determine the Rscon. Correlation analyzes were carried out between blast severity means on spikes of cultivars at 5, 7 and 11 dai and Rscon. The cultivars TBIO Mestre, TBIO Aton, ORS 1401, ORS 1403, ORS Destak, ORS Feroz, and CD 116 stood out for being classified in the statistical groups with the highest resistance to blast for the four variables considered in the study. The correlation between blast severity on spikes at 5, 7 and 11 dai and Rscon is at most moderate.

Adaptation of Fusarium Species causing Head Blight to Quantitative Resistance in Wheat: Field Evidence for Increased Aggressiveness in a New Pathogen Population

The use of quantitatively resistant wheat cultivars is an essential component of a sustainable management strategy of Fusarium head blight (FHB), caused by several Fusarium species. However, little information is available on the variation of aggressiveness of the newly emerging FHB collection compared to old one. It is therefore important to determine to what extent FHB populations can be selected for increased aggressiveness by wheat cultivars with several levels of quantitative resistance. To this end, FHB populations were sampled in 2005 (old population) and in 2015 (new population) from one of the major Syrian wheat production regions, chosen as a location where head blight occurs regularly. New and old FHB isolates were characterized for aggressiveness by single-floret inoculation under controlled conditions on eight durum and bread wheat cultivars of contrasting susceptibility to FHB, and molecularly distinguished using DNA markers. Results showed the new population caused a higher disease severity (ranging from 55% to 67%) than the old population. Thus, their aggressiveness increased between early and late samplings, suggesting that wheat plants cultivated over 10 years selected for increased aggressiveness during epidemics. Our comparative population genetic analyses with analyzed markers showed that the new population had more polymorphic loci compared with the old one. The information obtained in this study indicated that FHB populations adapt to prevailing wheat cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, quantitative resistance. Adaptation to wheat resulting in increased pathogen aggressiveness that was not specific may render quantitative resistance nondurable if not properly managed

Repeated exposure of wheat to the fungal root pathogen Bipolaris sorokiniana modulates rhizosphere microbiome assembly and disease suppressiveness

BackgroundDisease suppressiveness of soils to fungal root pathogens is typically induced in the field by repeated infections of the host plant and concomitant changes in the taxonomic composition and functional traits of the rhizosphere microbiome. Here, we studied this remarkable phenomenon for Bipolaris sorokiniana in two wheat cultivars differing in resistance to this fungal root pathogen.ResultsThe results showed that repeated exposure of the susceptible wheat cultivar to the pathogen led to a significant reduction in disease severity after five successive growth cycles. Surprisingly, the resistant wheat cultivar, initially included as a control, showed the opposite pattern with an increase in disease severity after repeated pathogen exposure. Amplicon analyses revealed that the bacterial families Chitinophagaceae, Anaerolineaceae and Nitrosomonadaceae were associated with disease suppressiveness in the susceptible wheat cultivar; disease suppressiveness in the resistant wheat cultivar was also associated with Chitinophagaceae and a higher abundance of Comamonadaceae. Metagenome analysis led to the selection of 604 Biosynthetic Gene Clusters (BGCs), out of a total of 2,571 identified by AntiSMASH analysis, that were overrepresented when the soil entered the disease suppressive state. These BGCs are involved in the biosynthesis of terpenes, non-ribosomal peptides, polyketides, aryl polyenes and post-translationally modified peptides.ConclusionCombining taxonomic and functional profiling we identified key changes in the rhizosphere microbiome during disease suppression. This illustrates how the host plant relies on the rhizosphere microbiome as the first line of defense to fight soil-borne pathogens. Microbial taxa and functions identified here can be used in novel strategies to control soil-borne fungal pathogens.

How to Differentiate between Resistant and Susceptible Wheat Cultivars for Leaf Rust Fungi Using Antioxidant Enzymes and Histological and Molecular Studies?

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.

Genome-wide association analysis of type II resistance to Fusarium head blight in common wheat.

Fusarium head blight (FHB) is a disease affecting wheat spikes caused by some Fusarium species and leads to cases of severe yield reduction and seed contamination. Identifying resistance genes/QTLs from wheat germplasm may help to improve FHB resistance in wheat production. Our study evaluated 205 elite winter wheat cultivars for FHB resistance. A high-density 90K SNP array was used for genotyping the panel. A genome-wide association study (GWAS) from cultivars from three different environments was performed using a mixed linear model (MLM). Sixty-six significant marker-trait associations (MTAs) were identified (P<0.001) on fifteen chromosomes that explained the phenotypic variation ranging from 5.4 to 11.2%. Some important new MTAs in genomic regions involving FHB resistance were found on chromosomes 2A, 3B, 5B, 6A, and 7B. Six MTAs at 92 cM on chromosome 7B were found in cultivars from two different environments. Moreover, there were 11 MTAs consistently associated with diseased spikelet rate and diseased rachis rate as pleiotropic effect loci and D_contig74317_533 on chromosome 5D was novel for FHB resistance. Eight new candidate genes of FHB resistance were predicated in wheat in this study. Three candidate genes, TraesCS5D02G006700, TraesCS6A02G013600, and TraesCS7B02G370700 on chromosome 5DS, 6AS, and 7BL, respectively, were perhaps important in defending against FHB by regulating intramolecular transferase activity, GTP binding, or chitinase activity in wheat, but further validation in needed. In addition, a total of five favorable alleles associated with wheat FHB resistance were discovered. These results provide important genes/loci for enhancing FHB resistance in wheat breeding by marker-assisted selection.

Comparative transcriptomic analysis of wheat cultivars differing in their resistance to Fusarium head blight infection during grain-filling stages reveals unique defense mechanisms at play

Fusarium head blight (FHB) is a devastating fungal disease that poses a significant threat to wheat production, causing substantial yield losses. Understanding the molecular mechanisms of wheat resistance to FHB is crucial for developing effective disease management strategies. This study aimed to investigate the mechanisms of FHB resistance and the patterns of toxin accumulation in three wheat cultivars, Annong8455, Annong1589, and Sumai3, with different levels of resistance, ranging from low to high respectively, under natural field conditions. Samples were taken at three different grain-filling stages (5, 10, and 15 DPA) for gene expression analysis and phenotypic observation. Results found that toxin concentration was inversely correlated with varietal resistance but not correlated with disease phenotypes, indicating that toxin analysis is a more accurate measure of disease status in wheat ears and grains. Transcriptomic data showed that Sumai3 exhibited a stronger immune response during all stages of grain filling by upregulating genes involved in the active destruction of pathogens and removal of toxins. In contrast, Annong1589 showed a passive prevention of the spread of toxins into cells by the upregulation of genes involved in tyramine biosynthesis at the early stage (5 DPA), which may be involved in cell wall strengthening. Our study demonstrates the complexity of FHB resistance in wheat, with cultivars exhibiting unique and overlapping defense mechanisms, and highlights the importance of considering the temporal and spatial dynamics of gene expression in breeding programs for developing more resistant wheat cultivars.

Resistance and Tolerance Screening of Spring Wheat Cultivars to Cereal Cyst Nematode (Heterodera avenae) in Southeastern Idaho.

Increased populations of Heterodera avenae in southeastern Idaho are associated with increased planting of susceptible cereal cultivars and lack of crop rotation. Identifying high-yield, resistant spring wheat cultivars with tolerance requires testing new genotypes and susceptibility assessments of marketed cultivars. We conducted two experiments to determine whether cultivars with putative resistance could maintain acceptable yield in the presence of H. avenae. We also evaluated the tolerance response in relation to previously tested cultivars. Seven spring wheat cultivars were planted in two irrigated commercial fields that were naturally infested with high populations of H. avenae. Measures of resistance, tolerance, and grain yield were assessed in aldicarb-treated versus nontreated plots. In aldicarb-treated plots in both years, grain yield of the susceptible cultivars Snow Crest, WestBred 936, WB9411, Patwin-515, and WB9668 was significantly increased. The expected yield increase with aldicarb was limited for the moderately susceptible Expresso due to water stress. 'WB-Rockland', carrying the Cre5 resistance gene, maintained its standard yield, while none of the other cultivars in the experiment showed resistance or tolerance. Our results indicated that aldicarb improves wheat grain yield in irrigated crop production systems, and although removed from the market, it is effective and has utility for research. The results also support the hypothesis that high yield susceptible cultivars can mask the effect of H. avenae on grain yield when managed appropriately.

Insights into the Aggressiveness of the Emerging North American Population 3 (NA3) of Fusarium graminearum.

In the United States and Canada, Fusarium graminearum (Fg) is the predominant etiological agent of Fusarium head blight (FHB), an economically devastating fungal disease of wheat and other small grains. Besides yield losses, FHB leads to grain contamination with trichothecene mycotoxins that are harmful to plant, human, and livestock health. Three genetic North American populations of Fg, differing in their predominant trichothecene chemotype (i.e., NA1/15ADON, NA2/3ADON, and NA3/NX-2), have been identified. To improve our understanding of the newly discovered population NA3 and how population-level diversity influences FHB outcomes, we inoculated heads of the moderately resistant wheat cultivar Alsen with 15 representative strains from each population and evaluated disease progression, mycotoxin accumulation, and mycotoxin production per unit Fg biomass. Additionally, we evaluated population-specific differences in induced host defense responses. The NA3 population was significantly less aggressive than the NA1 and NA2 populations but posed a similar mycotoxigenic potential. Multiomics analyses revealed patterns in mycotoxin production per unit Fg biomass, expression of Fg aggressiveness-associated genes, and host defense responses that did not always correlate with the NA3-specific severity difference. Our comparative disease assay of NA3/NX-2 and admixed NA1/NX-2 strains indicated that the reduced NA3 aggressiveness is not due solely to the NX-2 chemotype. Notably, the NA1 and NA2 populations did not show a significant advantage over NA3 in perithecia production, a fitness-related trait. Together, our data highlight that the disease outcomes were not due to mycotoxin production or host defense alone, indicating that other virulence factors and/or host defense mechanisms are likely involved.

Seed Transmission of Wheat Streak Mosaic Virus and Triticum Mosaic Virus in Differentially Resistant Wheat Cultivars.

Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are important viral pathogens of wheat in the Great Plains. These viruses individually or in mixed infections with High Plains wheat mosaic virus cause a devastating wheat streak mosaic (WSM) disease. Although seed transmission of WSMV has been studied, no information is currently available on that of TriMV. Furthermore, no study has explored the implications of mixed infections of WSMV and TriMV on seed transmission of one or both viruses. To study both aspects, seeds from differentially resistant field-grown wheat plants (cv. TAM 304 (susceptible), Joe (WSMV resistant, Wsm2 gene), and Breakthrough (BT) (WSMV and TriMV resistant, Wsm1 gene)) showing characteristic WSM symptoms were collected and analyzed to quantify both viruses using qRT-PCR. The percentage of seeds tested positive for WSMV or TriMV individually and in mixed infection varied with cultivar and virus combinations; 13% of TAM 304 seeds tested positive for WSMV, followed by 8% of BT and 4% of Joe seeds. Similarly, TriMV was detected in 12% of BT seeds, followed by 11% of TAM 304 and 8% of Joe seeds. Lastly, mixed infection was detected in 7% of TAM 304 seeds, followed by 4% in BT, and 2% in Joe. Dissection of field-collected seeds into three parts, embryo, endosperm, and seed coat, revealed both WSMV and TriMV accumulated only in the seed coat. Consistent with seeds, percent infection of WSMV or TriMV in the plants that emerged from infected seeds in each treatment varied with cultivar and virus combinations (WSMV: BT 3%; Joe 2%; TAM 304 9%; TriMV: BT 7%; Joe 8%; and TAM 304 10%). Plants infected with mixed viruses showed more pronounced WSM symptoms compared to individual infections. However, both viruses were present only in a few plants (BT: 2%, Joe: 1%, and TAM 304: 4%). Taken together, this study showed that TriMV was transmitted vertically at a higher frequency than WSMV in resistant cultivars, and the seed transmission of TriMV with WSMV increased the virulence of both pathogens (measured via WSM symptom severity) in the emerged plants. Furthermore, Wsm1 and Wsm2 genes considerably reduced WSMV transmission via infected seeds. However, no such effects were observed on TriMV, especially in progeny plants. These results reiterated the importance of planting clean seeds and highlighted the immediate need to identify/develop new sources of TriMV resistance to effectively manage the recurring WSM epidemic.

Sequencing trait-associated mutations to clone wheat rust-resistance gene YrNAM

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), can significantly affect wheat production. Cloning resistance genes is critical for efficient and effective breeding of stripe rust resistant wheat cultivars. One resistance gene (Yr10CG) underlying the Pst resistance locus Yr10 has been cloned. However, following haplotype and linkage analyses indicate the presence of additional Pst resistance gene(s) underlying/near Yr10 locus. Here, we report the cloning of the Pst resistance gene YrNAM in this region using the method of sequencing trait-associated mutations (STAM). YrNAM encodes a non-canonical resistance protein with a NAM domain and a ZnF-BED domain. We show that both domains are required for resistance. Transgenic wheat harboring YrNAM gene driven by its endogenous promoter confers resistance to stripe rust races CYR32 and CYR33. YrNAM is an ancient gene and present in wild wheat species Aegilops longissima and Ae. sharonensis; however, it is absent in most wheat cultivars, which indicates its breeding value.

Silicon amendments reduce aphid numbers and improve yield of aphid-resistant and susceptible wheat cultivars in a dose-dependent manner

Silicon (Si) is a non-essential element for plant growth and development that can increase plant resistance to insect pests in both susceptible and constitutively resistant cultivars. Three field experiments were carried out testing wheat cultivars with different levels of constitutive resistance to the aphid Sitobion avenae to evaluate the effect of Si application to the soil on the pest aphid's numbers and yield. The first field experiment (2012) was carried out with the wheat cultivars BRS 254, BRS 264 (both susceptible) and BRS TIMBAÚVA (resistant to S. avenae). The second (2014) and the third field experiment (repeated twice in 2015) evaluated the effect of Si doses (50, 100, 150 and 200 kg of Si ha−1) in BRS 254 and BRS TIMBAÚVA (in the second experiment in 2014), and in BRS 254 (in the third experiment). The three wheat varieties tested were responsive to silicate amendment, yielding higher grain weight, more grains per ear, and a higher percentage of Si in the shoot following Si soil amendment. Higher levels of Si in the soil had a linear relationship with increased grain yield and had a quadratic relationship with lower aphid numbers, both in the resistant variety (BRS Timbaúva) and in all tests with the susceptible variety (BRS 254). The application of Si to the soil increased productivity and increased resistance in wheat cultivars with varying levels of resistance. Si amendment is a potential tool for management of S. avenae in wheat.

Spatiotemporal patterns of wheat response to Pyrenophora tritici-repentis in asymptomatic regions revealed by transcriptomic and X-ray fluorescence microscopy analyses.

Pathogen attacks elicit dynamic and widespread molecular responses in plants. While our understanding of plant responses has advanced considerably, little is known of the molecular responses in the asymptomatic "green" regions (AGR) adjoining lesions. Here, we explore gene expression data and high-resolution elemental imaging to report the spatiotemporal changes in the AGR of susceptible and moderately resistant wheat cultivars infected with a necrotrophic fungal pathogen, Pyrenophora tritici-repentis (Ptr). We show, with improved spatiotemporal resolution, that calcium oscillations are modified in the susceptible cultivar, resulting in "frozen" host defence signals at the mature disease stage, and silencing of the host's recognition and defence mechanisms which would otherwise protect it from further attacks. In contrast, Ca accumulation and heightened defence response was observed in the moderately resistant cultivar in the later stage of disease development. Furthermore, in the susceptible interaction, the AGR was unable to recover post disease disruption. Our targeted sampling technique also enabled detection of eight previously predicted proteinaceous effectors in addition to the known ToxA effector. Collectively, our results highlight the benefits of spatially resolved molecular analysis and nutrient mapping to provide high-resolution spatiotemporal snapshots of host-pathogen interactions, paving the way for detangling complex disease interactions in plants.

Accumulation of complex oligosaccharides and CAZymes activity under acid conditions constitute the Thatcher+Lr9 defence responses to Puccinia triticina

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.