A novel quantitative trait locus for Fusarium head blight resistance in chromosome 7A of wheat

Transferring a new Fusarium head blight resistance locus FhbRc1 from Roegneria ciliaris into wheat by developing alien translocation lines

A new FHB resistance locus FhbRc1 was identified from the R. ciliaris chromosome 7S^c and transferred into common wheat by developing alien translocation lines. Fusarium head blight (FHB) caused by multiple Fusarium species is a globally destructive disease of common wheat. Exploring and utilization of resources with FHB resistance are the most effective and environmentally beneficial approach for the disease control. Roegneria ciliaris (Trin.) Nevski (2n = 4x = 28, S^cS^cY^cY^c), a tetraploid wheat wild relative, possesses high resistance to FHB. In the previous study, a complete set of wheat-R. ciliaris disomic addition (DA) lines were evaluated for FHB resistance. DA7S^c had stable FHB resistance, which was confirmed to be derived from alien chromosome 7S^c. We tentatively designated the resistant locus as FhbRc1. For better utilization of the resistance in wheat breeding, we developed translocations by inducing chromosome structural aberrations using iron irradiation and the homologous pairing gene mutant ph1b. Totally, 26 plants having various 7S^c structural aberrations were identified. By marker analysis, a cytological map of 7S^c was constructed and 7S^c was dissected into 16 cytological bins. Seven alien chromosome aberration lines, which all had the bin 7S^c-1 on the long arm of 7S^c, showed enhanced FHB resistance. Thus, FhbRc1 was mapped to the distal region of 7S^cL. A homozygous translocation line T4BS·4BL-7S^cL (NAURC001) was developed. It showed improved FHB resistance, while had no obvious genetic linkage drag for the tested agronomic traits compared with the recurrent parent Alondra's. When transferring the FhbRc1 into three different wheat cultivars, the derived progenies having the translocated chromosome 4BS·4BL-7S^cL all showed improved FHB resistance. This revealed the potential value of the translocation line in wheat breeding for FHB resistance.

Mapping Quantitative Trait Loci for Type II Fusarium Head Blight Resistance in Two Wheat Recombinant Inbred Line Populations Derived from Yangmai 4 and Yangmai 5

Fusarium head blight (FHB) is a destructive wheat disease worldwide and significantly affects grain yield and quality in wheat. To understand the genetic basis underlying type II FHB resistance in two elite wheat cultivars-Yangmai 4 (YM4) and Yangmai 5 (YM5)-quantitative trait loci (QTL) mapping was conducted in two recombinant inbred line (RIL) populations derived from the crosses of YM4 and YM5 with susceptible cultivar Yanzhan 1 (YZ1), respectively. A survey with markers linked to Fhb1, Fhb2, Fhb4, and Fhb5 in landrace Wangshuibai indicated the nonexistence of these known FHB resistance genes or QTL in YM4, YM5, and YZ1. One overlapped resistance QTL was identified in both RIL populations (namely, QFhb.Y4.2D/QFhb.Y5.2D) with a large effect on FHB resistance. One novel resistance QTL (QFhb.Y4.5A) mapped on chromosome 5A was detected only in the YM4/YZ1 population. The resistance alleles of both QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A did not increase the plant height and did not significantly affect the heading date and flowering date. Kompetitive allele-specific PCR markers for QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A had been developed to verify in an additional set of 244 geographically diverse cultivars or lines. Pyramiding of the two resistance alleles decreased the percentage of symptomatic spikelets by 51.77% relative to the cultivars or lines without these two resistance alleles. QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A were shown to be useful alternatives in FHB resistance breeding programs. The results will facilitate marker-assisted selection for introgression of the favorable alleles for improving FHB resistance in breeding programs.

Molecular Mapping of Quantitative Trait Loci for Fusarium Head Blight Resistance in the Brazilian Spring Wheat Cultivar "Surpresa"

Fusarium head blight (FHB) is a devastating disease in wheat. The use of resistant germplasm from diverse sources can significantly improve resistance to the disease. "Surpresa" is a Brazilian spring wheat cultivar with moderate FHB resistance, different from currently used sources. In this study, we aimed to identify and map the genetic loci for FHB resistance in Surpresa. A mapping population consisting of 187 recombinant inbred lines (RILs) was developed from a cross between Surpresa and a susceptible spring wheat cultivar, "Wheaton." The population was evaluated for FHB by the point-inoculation method in three greenhouse experiments and four field trials between 2016 and 2018. Mean disease severity for Surpresa and Wheaton was 41.2 and 84.9% across the 3 years of experiments, ranging from 30.3 to 59.1% and 74.3 to 91.4%, respectively. The mean FHB severity of the NILs was 57%, with an overall range from 7 to 100%, suggesting transgressive segregation in the population. The population was genotyped using a two-enzyme genotyping-by-sequencing approach, and a genetic map was constructed with 5,431 single nucleotide polymorphism (SNP) markers. Four QTL for type II resistance were detected on chromosomes 3A, 5A, 6A, and 7A, explaining 10.4-14.4% of the total phenotypic variation. The largest effect QTL was mapped on chromosome 7A and explained 14.4% of the phenotypic variation; however, it co-localized with a QTL governing the days to anthesis trait. A QTL for mycotoxin accumulation was also detected on chromosome 1B, explaining 18.8% of the total phenotypic variation. The QTL for FHB resistance identified in the study may diversify the FHB resistance gene pool and increase overall resistance to the disease in wheat.

Pyramiding of Fusarium Head Blight Resistance Quantitative Trait Loci, Fhb1, Fhb4, and Fhb5, in Modern Chinese Wheat Cultivars

Wheat production is increasingly threatened by the fungal disease, Fusarium head blight (FHB), caused by Fusarium spp. The introduction of resistant varieties is considered to be an effective measure for containment of this disease. Mapping of FHB-resistance quantitative trait locus (QTL) has promoted marker-assisted breeding for FHB resistance, which has been difficult through traditional breeding due to paucity of resistance genes and quantitative nature of the resistance. The lab of Ma previously cloned Fhb1, which inhibits FHB spread within spikes, and fine mapped Fhb4 and Fhb5, which condition resistance to initial infection of Fusarium spp., from FHB-resistant indigenous line Wangshuibai (WSB). In this study, these three QTLs were simultaneously introduced into five modern Chinese wheat cultivars or lines with different ecological adaptations through marker-assisted backcross in early generations. A total of 14 introgression lines were obtained. All these lines showed significantly improved resistance to the fungal infection and disease spread in 2-year field trials after artificial inoculation. In comparison with the respective recipient lines, the Fhb1, Fhb4, and Fhb5 pyramiding could reduce the disease severity by 95% and did not systematically affect plant height, productive tiller number, kernel number per spike, thousand grain weight, flowering time, and unit yield (without Fusarium inoculation). These results indicated the great value of FHB-resistance QTLs Fhb1, Fhb4, and Fhb5 derived from WSB, and the feasibility and effectiveness of early generation selection for FHB resistance solely based on linked molecular markers.

Two Different Inoculation Methods Unveiled the Relative Independence of DON Accumulation in Wheat Kernels from Disease Severity on Spike after Infection by Fusarium Head Blight

Fusarium head blight (FHB) causes wheat yield loss and mycotoxin (deoxynivalenol, DON) accumulation in wheat kernel. Developing wheat cultivars with overall resistance to both FHB spread within a spike and DON accumulation in kernels is crucial for ensuring food security and food safety. Here, two relatively novel inoculation methods, bilateral floret inoculation (BFI) and basal rachis internode injection (BRII), were simultaneously employed to evaluate disease severity and DON content in kernels in a segregating population of recombinant inbred lines (RILs) developed from Ning 7840 (carrying Fhb1) and Clark (without Fhb1). Under both inoculation methods, four contrasting combinations of disease severity and DON content were identified: high severity/high DON (HSHD), high severity/low DON (HSLD), low severity/high DON (LSHD) and low severity/low DON (LSLD). Unexpectedly, the BRII method clearly indicated that disease severity was not necessarily relevant to DON concentration. The effects of Fhb1 on disease severity, and on DON concentrations, agreed very well across the two methods. Several lines carrying Fhb1 showed extremely higher severity and (or) DON content under both inoculation methods. The “Mahalanobis distance” (MD) method was used to rate overall resistance of a line by inclusion of both disease severity and DON content over both methods to select LSLD lines.

Identification of Fusarium head blight resistance loci in two Brazilian wheat mapping populations

Fusarium head blight (FHB) is a disease of wheat (Triticum aestivum L.) that causes major yield losses in South America, as well as many other wheat growing regions around the world. FHB results in low quality, contaminated grain due to the production of mycotoxins such as deoxynivalenol (DON). In Brazil, FHB outbreaks are increasing in frequency and are currently controlled by fungicides which are costly and potentially harmful to the wider environment. To identify the genetic basis of resistance to FHB in Brazilian wheat, two mapping populations (Anahuac 75 × BR 18-Terena and BR 18-Terena × BRS 179) segregating for FHB resistance were phenotyped and quantitative trait loci (QTL) analysis was undertaken to identify genomic regions associated with FHB-related traits. A total of 14 QTL associated with FHB visual symptoms were identified, each of which explained 3.7–17.3% of the phenotypic variance. Two of these QTL were stable across environments. This suggests FHB resistance in Anahuac 75, BR 18-Terena and BRS 179 is controlled by multiple genetic loci that confer relatively minor differences in resistance. A major, novel QTL associated with DON accumulation was also identified on chromosome 4B (17.8% of the phenotypic variance), as well as a major QTL associated with thousand-grain weight on chromosome 6B (16.8% phenotypic variance). These QTL could be useful breeding targets, when pyramided with major sources of resistance such as Fhb1, to improve grain quality and reduce the reliance on fungicides in Brazil and other countries affected by FHB.

Fusarium Head Blight and Rust Diseases in Soft Red Winter Wheat in the Southeast United States: State of the Art, Challenges and Future Perspective for Breeding

Among the biotic constraints to wheat (Triticum aestivum L.) production, fusarium head blight (FHB), caused by Fusarium graminearum, leaf rust (LR), caused by Puccinia triticina, and stripe rust (SR) caused by Puccinia striiformis are problematic fungal diseases worldwide. Each can significantly reduce grain yield while FHB causes additional food and feed safety concerns due to mycotoxin contamination of grain. Genetic resistance is the most effective and sustainable approach for managing wheat diseases. In the past 20 years, over 500 quantitative trait loci (QTLs) conferring small to moderate effects for the different FHB resistance types have been reported in wheat. Similarly, 79 Lr-genes and more than 200 QTLs and 82 Yr-genes and 140 QTLs have been reported for seedling and adult plant LR and SR resistance, respectively. Most QTLs conferring rust resistance are race-specific generally conforming to a classical gene-for-gene interaction while resistance to FHB exhibits complex polygenic inheritance with several genetic loci contributing to one resistance type. Identification and deployment of additional genes/QTLs associated with FHB and rust resistance can expedite wheat breeding through marker-assisted and/or genomic selection to combine small-effect QTL in the gene pool. LR disease has been present in the southeast United States for decades while SR and FHB have become increasingly problematic in the past 20 years, with FHB arguably due to increased corn acreage in the region. Currently, QTLs on chromosome 1B from Jamestown, 1A, 1B, 2A, 2B, 2D, 4A, 5A, and 6A from W14, Ning7840, Ernie, Bess, Massey, NC-Neuse, and Truman, and 3B (Fhb1) from Sumai 3 for FHB resistance, Lr9, Lr10, Lr18, Lr24, Lr37, LrA2K, and Lr2K38 genes for LR resistance, and Yr17 and YrR61 for SR resistance have been extensively deployed in southeast wheat breeding programs. This review aims to disclose the current status of FHB, LR, and SR diseases, summarize the genetics of resistance and breeding efforts for the deployment of FHB and rust resistance QTL on soft red winter wheat cultivars, and present breeding strategies to achieve sustainable management of these diseases in the southeast US.

Fusarium head blight in wheat: contemporary status and molecular approaches

Fusarium head blight (FHB) disease that occurs in wheat is caused by Fusarium graminearum and is a major risk to wheat yield. Although several research efforts focusing on FHB have been conducted in the past several decades, conditions have become more critical due to the increase in its virulent forms. In such a scenario, conferring complete resistance in plants seems to be difficult for handling this issue. The phenotyping for FHB and finding a solution for it at the genetic level comprises a long-term process as FHB infection is largely affected by environmental conditions. Modern molecular strategies have played a crucial role in revealing the host-pathogen interaction in FHB. The integration of molecular biology-based methods such as genome-wide association studies and marker-based genomic selection has provided potential cultivars for breeding programs. In this review, we aim at outlining the contemporary status of the studies conducted on FHB in wheat. The influence of FHB in wheat on animals and human health is also discussed. In addition, a summary of the advancement in the molecular technologies for identifying and developing the FHB-resistant wheat genetic resources is provided. It also suggests the future measures that are required to reduce the world's vulnerability to FHB which was one of the main goals of the US Wheat and Barley Scab Initiative.

QTL mapping and successful introgression of the spring wheat-derived QTL Fhb1 for Fusarium head blight resistance in three European triticale populations

KEY MESSAGE

The spring wheat-derived QTL Fhb1 was successfully introgressed into triticale and resulted in significantly improved FHB resistance in the three triticale mapping populations. Fusarium head blight (FHB) is a major problem in cereal production particularly because of mycotoxin contaminations. Here we characterized the resistance to FHB in triticale breeding material harboring resistance factors from bread wheat. A highly FHB-resistant experimental line which derives from a triticale × wheat cross was crossed to several modern triticale cultivars. Three populations of recombinant inbred lines were generated and evaluated in field experiments for FHB resistance using spray inoculations during four seasons and were genotyped with genotyping-by-sequencing and SSR markers. FHB severity was assessed in the field by visual scorings and on the harvested grain samples using digital picture analysis for quantifying the whitened kernel surface (WKS). Four QTLs with major effects on FHB resistance were identified, mapping to chromosomes 2B, 3B, 5R, and 7A. Those QTLs were detectable with both Fusarium severity traits. Measuring of WKS allows easy and fast grain symptom quantification and appears as an effective scoring tool for FHB resistance. The QTL on 3B collocated with Fhb1, and the QTL on 5R with the dwarfing gene Ddw1. This is the first report demonstrating the successful introgression of Fhb1 into triticale. It comprises a significant step forward for enhancing FHB resistance in this crop.

Trichothecenes in Cereal Grains - An Update

Trichothecenes are sesquiterpenoid mycotoxins produced by fungi from the order Hypocreales, including members of the Fusarium genus that infect cereal grain crops. Different trichothecene-producing Fusarium species and strains have different trichothecene chemotypes belonging to the Type A and B class. These fungi cause a disease of small grain cereals, called Fusarium head blight, and their toxins contaminate host tissues. As potent inhibitors of eukaryotic protein synthesis, trichothecenes pose a health risk to human and animal consumers of infected cereal grains. In 2009, Foroud and Eudes published a review of trichothecenes in cereal grains for human consumption. As an update to this review, the work herein provides a comprehensive and multi-disciplinary review of the Fusarium trichothecenes covering topics in chemistry and biochemistry, pathogen biology, trichothecene toxicity, molecular mechanisms of resistance or detoxification, genetics of resistance and breeding strategies to reduce their contamination of wheat and barley.

Detection and validation of a novel major QTL for resistance to Fusarium head blight from Triticum aestivum in the terminal region of chromosome 7DL

A novel QTL for FHB resistance was mapped on wheat 7DL, being effective in multiple genetic backgrounds and environments, and comparable to Fhb1 in effect magnitude. Fusarium head blight (FHB) is one of the major fungal diseases affecting wheat production in many countries. The wheat line AQ24788-83 (AQ) possesses FHB resistance. The American wheat cultivar Luke is FHB susceptible. A Luke × AQ population consisting of 1652 advanced recombinant inbred lines (RILs) was developed, from which 272 RILs were randomly sampled and used to construct a linkage map. Another 154 RILs were selected for homogeneity in plant height (PH) and flowering date (FD). This selection strategy was adopted to reduce possible confounding effects on FHB assessment due to variation in PH and FD. The 272 and 154 RILs were genotyped applying simple sequence repeat (SSR), diversity arrays technology (DArT) and single-nucleotide polymorphism (SNP) markers. The two sets of RILs were evaluated for FHB resistance applying point inoculation in greenhouses; the 154 RILs were also evaluated applying spray inoculation in multiple field environments. The linkage map consisted of 2088 SSR, DArT, and SNP markers. A FHB resistance quantitative trait locus (QTL), designated as QFhb.cau-7DL, was detected on chromosome arm 7DL; this QTL was closely linked to the SSR marker gwm428 ( http://www.wheat.pw.usda.gov/ggpages/SSR/ ). QFhb.cau-7DL was significantly effective (α = 0.01) in every test trial, and its effectiveness was validated using three additional wheat crosses. Sumai 3 (donor wheat of the FHB resistance gene Fhb1) was used in one of these crosses. QFhb.cau-7DL was comparable to Fhb1 in effect magnitude, providing a great potential for improving FHB resistance.

Meta-Analysis of the QTLome of Fusarium Head Blight Resistance in Bread Wheat: Refining the Current Puzzle

Background: Fusarium Head Blight (FHB) is a worldwide devastating disease of bread wheat (Triticum aestivum L.). Genetic resistance is the most effective way to control FHB and many QTL related to this trait have been mapped on the wheat genetic map. This information, however, must be refined to be more efficiently used in breeding programs and for the advance of the basic research. The objective of the present study was to in-depth analyze the QTLome of FHB resistance in bread wheat, further integrating genetic, genomic, and transcriptomic data, aiming to find candidate genes. Methods: An exhaustive bibliographic review on 76 scientific papers was carried out collecting information about QTL related to FHB resistance mapped on bread wheat. A dense genetic consensus map with 572,862 loci was generated for QTL projection. Meta-analysis could be performed on 323 QTL. Candidate gene mining was carried out within the most refined loci, containing genes that were cross-validated with publicly available transcriptional expression data of wheat under Fusarium infection. Most highlighted genes were investigated for protein evidence. Results: A total of 556 QTL were found in the literature, distributed on all sub-genomes and chromosomes of wheat. Meta-analysis generated 65 meta-QTL, and this refinement allows one to find markers more tightly linked to these regions. Candidate gene mining within the most refined meta-QTL, meta-QTL 1/chr. 3B, harvested 324 genes and transcriptional data cross-validated 10 of these genes, as responsive to FHB. One is of these genes encodes a Glycosiltransferase and the other encodes for a Cytochrome P450, and these such proteins have already been verified as being responsible for FHB resistance, but the remaining eight genes still have to be further studied, as promising loci for breeding. Conclusions: The QTLome of FHB resistance in wheat was successfully assembled and a refinement in terms of number and length of loci was obtained. The integration of the QTLome with genomic and transcriptomic data has allowed for the discovery of promising candidate genes for use in breeding programs.

Construction of new EST-SSRs for Fusarium resistant wheat breeding

Surveying Fusarium resistance in wheat with easy applicable molecular markers such as simple sequence repeats (SSRs) is a prerequest for molecular breeding. Expressed sequence tags (ESTs) are one of the main sources for development of new SSR candidates. Therefore, 18.292 publicly available wheat ESTs were mined and genotyping of newly developed 55 EST-SSR derived primer pairs produced clear fragments in ten wheat cultivars carrying different levels of Fusarium resistance. Among the proved markers, 23 polymorphic EST-SSRs were obtained and related alleles were mostly found on B and D genome. Based on the fragment profiling and similarity analysis, a 327bp amplicon, which was a product of contig 1207 (chromosome 5BL), was detected only in Fusarium head blight (FHB) resistant cultivars (CM82036 and Sumai) and the amino acid sequences showed a similarity to pathogen related proteins. Another FHB resistance related EST-SSR, Contig 556 (chromosome 1BL) produced a 151bp fragment in Sumai and was associated to wax2-like protein. A polymorphic 204bp fragment, derived from Contig 578 (chromosome 1DL), was generated from root rot (FRR) resistant cultivars (2-49; Altay2000 and Sunco). A total of 98 alleles were displayed with an average of 1.8 alleles per locus and the polymorphic information content (PIC) ranged from 0.11 to 0.78. Dendrogram tree with two main and five sub-groups were displayed the highest genetic relationship between FRR resistant cultivars (2-49 and Altay2000), FRR sensitive cultivars (Seri82 and Scout66) and FHB resistant cultivars (CM82036 and Sumai). Thus, exploitation of these candidate EST-SSRs may help to genotype other wheat sources for Fusarium resistance.

Effective marker alleles associated with type 2 resistance to Fusarium head blight infection in fields

Molecular markers associated with known quantitative trait loci (QTLs) for type 2 resistance to Fusarium head blight (FHB) in bi-parental mapping population usually have more than two alleles in breeding populations. Therefore, understanding the association of each allele with FHB response is particularly important to marker-assisted enhancement of FHB resistance. In this paper, we evaluated FHB severities of 192 wheat accessions including landraces and commercial varieties in three field growing seasons, and genotyped this panel with 364 genome-wide informative molecular markers. Among them, 11 markers showed reproducible marker-trait association (p < 0.05) in at least two experiments using a mixed model. More than two alleles were identified per significant marker locus. These alleles were classified into favorable, unfavorable and neutral alleles according to the normalized genotypic values. The distributions of effective alleles at these loci in each wheat accession were characterized. Mean FHB severities increased with decreased number of favorable alleles at the reproducible loci. Chinese wheat landraces and Japanese accessions have more favorable alleles at the majority of the reproducible marker loci. FHB resistance levels of varieties can be greatly improved by introduction of these favorable alleles and removal of unfavorable alleles simultaneously at these QTL-linked marker loci.

Host to a Stranger: Arabidopsis and Fusarium Ear Blight

Fusarium ear blight (FEB) is a devastating fungal disease of cereal crops. Outbreaks are sporadic and current control strategies are severely limited. This review highlights the use of Arabidopsis to study plant-FEB interactions. Use of this pathosystem has identified natural variation in Fusarium susceptibility in Arabidopsis, and native plant genes and signalling processes modulating the interaction. Recent breakthroughs include the identification of plant- and insect-derived small molecules which increase disease resistance, and the use of a host-induced gene silencing (HIGS) construct to silence an important Fusarium gene to prevent infection. Arabidopsis has also been used to study other fungi that cause cereal diseases. These findings offer the potential for translational research in cereals which could yield much-needed novel control strategies.

Breeding healthy cereals: genetic improvement of Fusarium resistance and consequences for mycotoxins

Although it is generally agreed that increased genetic resistance to fungal colonisation by Fusarium head blight (FHB) should lead to reduced damage and particularly to reduced contamination due to mycotoxins, this review aims to highlight on this relation based on published literature in comparison to our own results. We focus here on the major cereal crop plants wheat and barley. Generally, correlations between measures for disease severity on the plants or the seeds and toxin content were found positive and significant. Breeding of new cultivars with reduced Fusarium disease severity will therefore lead to a correlated selection response in the direction of reduced toxin contamination, for the prevalent toxins such as deoxynivalenol, but also for less abundant mycotoxins and masked mycotoxins. Choosing resistant cultivars is possibly the best option for mycotoxin reduction right at the beginning of the cereal production chain: on the farmer’s field. Therefore, investment in breeding FHB resistant cultivars will contribute to sustainable reduction of the mycotoxin problems in the cereal production chain, and increase food and feed safety.

A New Map Location of Gene Stb3 for Resistance to Septoria Tritici Blotch in Wheat

Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (synonym: Zymoseptoria tritici; asexual stage: Septoria tritici), is an important disease of wheat worldwide. Management of the disease usually is by host resistance or fungicides. However, M. graminicola has developed insensitivity to most commonly applied fungicides so there is a continuing need for well-characterized sources of host resistance to accelerate the development of improved wheat cultivars. Gene Stb3 has been a useful source of major resistance, but its mapping location has not been well characterized. Based on linkage to a single marker, a previous study assigned Stb3 to a location on the short arm of chromosome 6D. However, the results from the present study show that this reported location is incorrect. Instead, linkage analysis revealed that Stb3 is located on the short arm of wheat chromosome 7A, completely linked to microsatellite (SSR) locus Xwmc83 and flanked by loci Xcfa2028 (12.4 cM distal) and Xbarc222 (2.1 cM proximal). Linkage between Stb3 and Xwmc83 was validated in BC₁F₃ progeny of other crosses, and analyses of the flanking markers with deletion stocks showed that the gene is located on 7AS between fraction lengths 0.73 and 0.83. This revised location of Stb3 is different from those for other STB resistance genes previously mapped in hexaploid wheat but is approximately 20 cM proximal to an STB resistance gene mapped on the short arm of chromosome 7A^m in Triticum monococcum. The markers described in this study are useful for accelerating the deployment of Stb3 in wheat breeding programs.

Mutations in the Arabidopsis homoserine kinase gene DMR1 confer enhanced resistance to Fusarium culmorum and F. graminearum

BACKGROUND

Mutation of Arabidopsis DMR1, encoding homoserine kinase, leads to elevation in homoserine and foliar resistance to the biotrophic pathogens Hyaloperonospora arabidopsidis and Oidium neolycopersici through activation of an unidentified defence mechanism. This study investigates the effect of mutation of dmr1 on resistance to the ascomycete pathogens Fusarium graminearum and F. culmorum, which cause Fusarium Ear Blight (FEB) disease on small grain cereals.

RESULTS

We initially found that the dmr1-2 mutant allele confers increased resistance to F. culmorum and F. graminearum silique infection, and decreased colonisation of rosette leaves. Meanwhile the dmr1-1 allele supports less rosette leaf colonisation but has wild type silique resistance. Three additional dmr1 alleles were subsequently examined for altered F. culmorum susceptibility and all showed increased silique resistance, while leaf colonisation was reduced in two (dmr1-3 and dmr1-4). Amino acid analysis of dmr1 siliques revealed homoserine accumulation, which is undetectable in wild type plants. Exogenous application of L-homoserine reduced bud infection in both dmr1 and wild type plants, whilst D-homoserine application did not. Delayed leaf senescence was also observed in dmr1 plants compared to wild type and correlated with reduced Fusarium leaf colonisation.

CONCLUSIONS

These findings suggest that common Arabidopsis DMR1 mediated susceptibility mechanisms occur during infection by both obligate biotrophic oomycete and hemi-biotrophic fungal pathogens, not only in vegetative but also in reproductive plant tissues. This has the potential to aid the development of cereal crops with enhanced resistance to FEB.

Transcriptome profiling of wheat differentially expressed genes exposed to different chemotypes of Fusarium graminearum

The study is an overview of the behavior of the wheat transcriptome to the Fusarium graminearum fungus using two different chemotypes. The transcriptome profiles of seven putative differentially expressed defense-related genes were identified by SSH and further examined using qPCR. Fusarium head blight (FHB) of wheat (Triticum aestivum L.), caused by several species of the fungus fusarium, is important in all wheat growing regions worldwide. The most dominant species in Canada is Fusarium graminearum (Fg). F. graminearum isolates producing mycotoxins such as 3-acetyl-deoxynivalenol (3ADON) and 15-acetyl-deoxynivalenol (15ADON). The objective of this study was to investigate the effect of the different chemotypes of Fg on the transcriptome pattern of expressed wheat genes. A cDNA library was constructed from infected "Sumai 3" spikes harvested at different times after inoculation with a macroconidia suspension. Employing suppression subtractive hybridization (SSH), the subtracted cDNA library was differentially screened by dot-blot hybridization. Thirty-one clones were identified; one was isolated and characterized, and transcriptome profiling of seven up-regulated putative defense-related genes was performed using quantitative real-time reverse-transcriptase PCR. These genes may be involved in the wheat-pathogen interactions revealing transcript accumulation differences between the non-diseased, 3ADON-, and 15ADON-infected plants. Additionally, significant differences in gene expression were observed between 3ADON- and 15ADON-infected plants which highlight the significance of a particular chemotype in FHB disease.

Whole genome association mapping of Fusarium head blight resistance in European winter wheat (Triticum aestivum L.)

A total of 358 recent European winter wheat varieties plus 14 spring wheat varieties were evaluated for resistance to Fusarium head blight (FHB) caused by Fusarium graminearum and Fusarium culmorum in four separate environments. The FHB scores based on FHB incidence (Type I resistance)×FHB severity (Type II resistance) indicated a wide phenotypic variation of the varieties with BLUE (best linear unbiased estimation) values ranging from 0.07 to 33.67. Genotyping with 732 microsatellite markers resulted in 782 loci of which 620 were placed on the ITMI map. The resulting average marker distance of 6.8 cM allowed genome wide association mapping employing a mixed model. Though no clear population structure was discovered, a kinship matrix was used for stratification. A total of 794 significant (-log10(p)-value≥3.0) associations between SSR-loci and environment-specific FHB scores or BLUE values were detected, which included 323 SSR alleles. For FHB incidence and FHB severity a total of 861 and 877 individual marker-trait associations (MTA) were detected, respectively. Associations for both traits co-located with FHB score in most cases. Consistent associations detected in three or more environments were found on all chromosomes except chromosome 6B, and with the highest number of MTA on chromosome 5B. The dependence of the number of favourable and unfavourable alleles within a variety to the respective FHB scores indicated an additive effect of favourable and unfavourable alleles, i.e. genotypes with more favourable or less unfavourable alleles tended to show greater resistance to FHB. Assessment of a marker specific for the dwarfing gene Rht-D1 resulted in strong effects. The results provide a prerequisite for designing genome wide breeding strategies for FHB resistance.

Anther extrusion and plant height are associated with Type I resistance to Fusarium head blight in bread wheat line 'Shanghai-3/Catbird'

Fusarium head blight (FHB) is a destructive wheat disease of global importance. Resistance breeding depends heavily on the Fhb1 gene. The CIMMYT line Shanghai-3/Catbird (SHA3/CBRD) is a promising source without this gene. A recombinant inbred line (RIL) population from the cross of SHA3/CBRD with the German spring wheat cv. Naxos was evaluated for FHB resistance and related traits in field trials using spray and spawn inoculation in Norway and point inoculation in China. After spray and spawn inoculation, FHB severities were negatively correlated with both anther extrusion (AE) and plant height (PH). The QTL analysis showed that the Rht-B1b dwarfing allele co-localized with a QTL for low AE and increased susceptibility after spawn and spray inoculation. In general, SHA3/CBRD contributed most of the favorable alleles for resistance to severity after spray and spawn inoculation, while Naxos contributed more favorable alleles for reduction in FDK and DON content and resistance to severity after point inoculation. SHA3/CBRD contributed a major resistance QTL close to the centromere on 2DLc affecting FHB severity and DON after all inoculation methods. This QTL was also associated with AE and PH, with high AE and tall alleles contributed by SHA3/CBRD. Several QTL for AE and PH were detected, and low AE or reduced PH was always associated with increased susceptibility after spawn and spray inoculation. Most of the other minor FHB resistance QTL from SHA3/CBRD were associated with AE or PH, while the QTL from Naxos were mostly not. After point inoculation, no other QTL for FHB traits was associated with AE or PH, except the 2DLc QTL which was common across all inoculation methods. Marker-assisted selection based on the 2DLc QTL from SHA3/CBRD combined with phenotypic selection for AE is recommended for resistance breeding based on this valuable source of resistance.