Barley traits associated with resistance to fusarium head blight and deoxynivalenol accumulation

Characterization of Fusarium species causing head blight of highland barley (qingke) in Tibet, China

Most of the research on the characterization of Fusarium species focused on wheat, barley, rice, and maize in China. However, there has been limited research in highland barley (qingke). Recently, Fusarium head blight (FHB) of qingke was recently observed in Tibet, China, especially around the Brahmaputra River. To gain a better understanding of the pathogens involver, 201 Fusarium isolates were obtained from qingke samples in 2020. Among these isolates, the most abundant species was F. avenaceum (45.3 %), followed by F. equiseti (27.8 %), F. verticillioides (13.9 %), F. acuminatum (9.0 %), F. flocciferum (3.5 %), and F. proliferatum (0.5 %). The distribution of Fusarium species varied along the Brahmaputra River, with F. avenaceum being predominant in the midstream and downstream regions, while F. equiseti was more common in the upstream region. Chemical analyses of all the isolates revealed the production of different mycotoxins by various Fusarium species. It was found that enniatins were produced by F. acuminatum, F. avenaceum, and F. flocciferum, beauvericin (BEA) and fumonisins were produced F. proliferatum and F. verticillioides, and zearalenone (ZEN) and nivalenol (NIV) were produced by F. equiseti. Pathogenicity test showed that F. avenaceum was more aggressive in causing FHB compared to F. acuminatum, F. equiseti, and F. flocciferum. The disease severity, measured by the area under the disease progress curve (AUDPC), was significantly positively (P < 0.01) correlated with the concentration of total toxins produced by each species. Furthermore, all the Fusarium strains which were used for pathogenicity test were susceptible to carbendazim, and the 50 % effective concentration (EC50) ranged from 0.406 μg/mL to 0.673 μg/mL with an average EC50 of 0.551 ± 0.012 μg/mL.

Evaluation of Barley and Wheat Germplasm for Resistance to Head Blight and Mycotoxin Production by Fusarium asiaticum and F. graminearum

Fusarium head blight (FHB) is one of the most serious diseases in barley and wheat, as it is usually accompanied by the production of harmful mycotoxins in the grains. To identify FHB-resistant breeding resources, we evaluated 60 elite germplasm accessions of barley (24) and wheat (36) for FHB and mycotoxin accumulation. Assessments were performed in a greenhouse and five heads per accession were inoculated with both Fusarium asiaticum (Fa73, nivalenol producer) and F. graminearum (Fg39, deoxynivalenol producer) strains. While the accessions varied in disease severity and mycotoxin production, four wheat and one barley showed <20% FHB severity repeatedly by both strains. Mycotoxin levels in these accessions ranged up to 3.9 mg/kg. FHB severity was generally higher in barley than in wheat, and Fa73 was more aggressive in both crops than Fg39. Fg39 itself, however, was more aggressive toward wheat and produced more mycotoxin in wheat than in barley. FHB severity by Fa73 and Fg39 were moderately correlated in both crops (r = 0.57/0.60 in barley and 0.42/0.58 in wheat). FHB severity and toxin production were also correlated in both crops, with a stronger correlation for Fa73 (r = 0.42/0.82 in barley, 0.70 in wheat) than for Fg39.

GPTransformer: A Transformer-Based Deep Learning Method for Predicting Fusarium Related Traits in Barley

Fusarium head blight (FHB) incited by Fusarium graminearum Schwabe is a devastating disease of barley and other cereal crops worldwide. Fusarium head blight is associated with trichothecene mycotoxins such as deoxynivalenol (DON), which contaminates grains, making them unfit for malting or animal feed industries. While genetically resistant cultivars offer the best economic and environmentally responsible means to mitigate disease, parent lines with adequate resistance are limited in barley. Resistance breeding based upon quantitative genetic gains has been slow to date, due to intensive labor requirements of disease nurseries. The production of a high-throughput genome-wide molecular marker assembly for barley permits use in development of genomic prediction models for traits of economic importance to this crop. A diverse panel consisting of 400 two-row spring barley lines was assembled to focus on Canadian barley breeding programs. The panel was evaluated for FHB and DON content in three environments and over 2 years. Moreover, it was genotyped using an Illumina Infinium High-Throughput Screening (HTS) iSelect custom beadchip array of single nucleotide polymorphic molecular markers (50 K SNP), where over 23 K molecular markers were polymorphic. Genomic prediction has been demonstrated to successfully reduce FHB and DON content in cereals using various statistical models. Herein, we have studied an alternative method based on machine learning and compare it with a statistical approach. The bi-allelic SNPs represented pairs of alleles and were encoded in two ways: as categorical (-1, 0, 1) or using Hardy-Weinberg probability frequencies. This was followed by selecting essential genomic markers for phenotype prediction. Subsequently, a Transformer-based deep learning algorithm was applied to predict FHB and DON. Apart from the Transformer method, a Residual Fully Connected Neural Network (RFCNN) was also applied. Pearson correlation coefficients were calculated to compare true vs. predicted outputs. Models which included all markers generally showed marginal improvement in prediction. Hardy-Weinberg encoding generally improved correlation for FHB (6.9%) and DON (9.6%) for the Transformer network. This study suggests the potential of the Transformer based method as an alternative to the popular BLUP model for genomic prediction of complex traits such as FHB or DON, having performed equally or better than existing machine learning and statistical methods.

Genetic dissection of a pericentromeric region of barley chromosome 6H associated with Fusarium head blight resistance, grain protein content and agronomic traits

Fine mapping of barley 6H pericentromeric region identified FHB QTL with opposite effects, and high grain protein content was associated with increased FHB severity. Resistance to Fusarium head blight (FHB), kernel discoloration (KD), deoxynivalenol (DON) accumulation and grain protein content (GPC) are important traits for breeding malting barley varieties. Previous work mapped a Chevron-derived FHB QTL to the pericentromeric region of 6H, coinciding with QTL for KD resistance and GPC. The Chevron allele reduced FHB and KD, but unfavorably increased GPC. To determine whether the correlations are caused by linkage or pleiotropy, a fine mapping approach was used to dissect the QTL underlying these quality and disease traits. Two populations, referred to as Gen10 and Gen10/Lacey, derived from a recombinant near-isogenic line (rNIL) were developed. Recombinants were phenotyped for FHB, KD, DON, GPC and other agronomic traits. Three FHB, two DON and two KD QTLs were identified. One of the three FHB QTLs, one DON QTL and one KD QTL were coincident with the GPC QTL, which contains the Hv-NAM1 locus affecting grain protein accumulation. The Chevron allele at the GPC QTL increased GPC and FHB and decreased DON and KD. The other two FHB QTL and the other DON and KD QTL were identified in the regions flanking the Hv-NAM1 locus, and the Chevron alleles decreased FHB, DON and KD. Our results suggested that the QTL associated with FHB, KD, DON and GPC in the pericentromeric region of 6H was controlled by both pleiotropy and tightly linked loci. The rNILs identified in this study with low FHB severity and moderate GPC may be used for breeding malting barley cultivars.

Mapping of quantitative trait loci for traits linked to fusarium head blight in barley

Fusarium head blight (FHB) is a devastating disease occurring in small grain cereals worldwide. The disease results in the reduction of grain yield, and mycotoxins accumulated in grain are also harmful to both humans and animals. It has been reported that response to pathogen infection may be associated with the morphological and developmental traits of the host plant, e.g. earliness and plant height. Despite many studies, effective markers for selection of barley genotypes with increased resistance to FHB have not been developed. In the present study, we investigated 100 recombinant inbred lines (RIL) of spring barley. Plants were examined in field conditions (three locations) in a completely randomized design with three replications. Barley genotypes were artificially infected with spores of Fusarium culmorum before heading. Apart from the main phenotypic traits (plant height, spike characteristic, grain yield), infected kernels were visually scored and the content of deoxynivalenol (DON) mycotoxin was investigated. A set of 70 Quantitative Trait Loci (QTLs) were detected through phenotyping of the mapping population in field conditions and genotyping using a barley Ilumina 9K iSelect platform. Six loci were detected for the FHB index on chromosomes 2H, 3H, 5H, and 7H. A region on the short arm of chromosome 2H was detected in which many QTLs associated with FHB- and yield-related traits were found. This study confirms that agromorphological traits are tightly related to FHB and should be taken into consideration when breeding barley plants for FHB resistance.

Development of a Multiparent Population for Genetic Mapping and Allele Discovery in Six-Row Barley

Germplasm collections hold valuable allelic diversity for crop improvement and genetic mapping of complex traits. To gain access to the genetic diversity within the USDA National Small Grain Collection (NSGC), we developed the Barley Recombinant Inbred Diverse Germplasm Population (BRIDG6), a six-row spring barley multiparent population (MPP) with 88 cultivated accessions crossed to a common parent (Rasmusson). The parents were randomly selected from a core subset of the NSGC that represents the genetic diversity of landrace and breeding accessions. In total, we generated 6160 F5 recombinant inbred lines (RILs), with an average of 69 and a range of 37-168 RILs per family, that were genotyped with 7773 SNPs, with an average of 3889 SNPs segregating per family. We detected 23 quantitative trait loci (QTL) associated with flowering time with five QTL found coincident with previously described flowering time genes. A major QTL was detected near the flowering time gene, HvPpd-H1 which affects photoperiod. Haplotype-based analysis of HvPpd-H1 identified private alleles to families of Asian origin conferring both positive and negative effects, providing the first observation of flowering time-related alleles private to Asian accessions. We evaluated several subsampling strategies to determine the effect of sample size on the power of QTL detection, and found that, for flowering time in barley, a sample size >50 families or 3000 individuals results in the highest power for QTL detection. This MPP will be useful for uncovering large and small effect QTL for traits of interest, and identifying and utilizing valuable alleles from the NSGC for barley improvement.

QTL Mapping of Fusarium Head Blight and Correlated Agromorphological Traits in an Elite Barley Cultivar Rasmusson

Fusarium head blight (FHB) is an important fungal disease affecting the yield and quality of barley and other small grains. Developing and deploying resistant barley cultivars is an essential component of an integrated strategy for reducing the adverse effects of FHB. Genetic mapping studies have revealed that resistance to FHB and the accumulation of pathogen-produced mycotoxins are controlled by many quantitative trait loci (QTL) with minor effects and are highly influenced by plant morphological traits and environmental conditions. Some prior studies aimed at mapping FHB resistance have used populations derived from crossing a Swiss landrace Chevron with elite breeding lines/cultivars. Both Chevron and Peatland, a sib-line of Chevron, were used as founders in the University of Minnesota barley breeding program. To understand the native resistance that might be present in the Minnesota breeding materials, a cross of an elite cultivar with a susceptible unadapted genotype is required. Here, a mapping population of 93 recombinant inbred lines (RILs) was developed from a cross between a moderately susceptible elite cultivar 'Rasmusson' and a highly susceptible Japanese landrace PI 383933. This population was evaluated for FHB severity, deoxynivalenol (DON) accumulation and various agromorphological traits. Genotyping of the population was performed with the barley iSelect 9K SNP chip and 1,394 SNPs were used to develop a genetic map. FHB severity and DON accumulation were negatively correlated with plant height (HT) and spike length (SL), and positively correlated with spike density (SD). QTL analysis using composite interval mapping (CIM) identified the largest effect QTL associated with FHB and DON on the centromeric region of chromosome 7H, which was also associated with HT, SL, and SD. A minor FHB QTL and a minor DON QTL were detected on chromosome 6H and chromosome 3H, respectively, and the Rasmusson alleles contributed to resistance. The 3H DON QTL likely represents native resistance in elite germplasm as the marker haplotype of Rasmusson at this QTL is distinct from that of Chevron. This study highlights the relationship between FHB resistance/susceptibility and morphological traits and the need for breeders to account for morphology when developing FHB resistant genotypes.

Fusarium infection and trichothecenes in barley and its comparison with wheat

Barley is a small-grain cereal that can be infected by Fusarium spp. resulting in reduced quality and safety of harvested barley (products). Barley and other small-grain cereals are commonly studied together for Fusarium infection and related mycotoxin contamination, since the infection and its influencing factors are assumed to be the same for all small-grain cereals. Using relevant literature, this study reviewed Fusarium spp. infection and mycotoxin contamination, mainly T-2/HT-2 toxin and deoxynivalenol (DON), in barley specifically. For the first time, review results provide an extensive overview of the influencing factors for Fusarium infection and mycotoxin production in barley, such as weather, agricultural management and processing factors, and includes the comparison of these mechanisms in wheat. Results showed that Fusarium infection in barley is difficult to recognise in the field and mycotoxin levels cannot be estimated based on the symptoms. These factors make it difficult to establish the real severity of Fusarium infection in barley. In addition, most pre-harvest measures to mitigate initial Fusarium infection, such as cultivar use and soil cultivation, are the same for barley and wheat, but due to anatomical differences, some pre-harvest measures have a different effect on Fusarium infection in barley. For example, the effective moment (days after anthesis) of fungicide application in barley and wheat is different. Also, in wheat, there is an additional effect of multiple fungicide applications in reducing Fusarium Head Blight and DON concentrations, whereas in barley, no additional effect of multiple application is seen. Hence, care should be taken to use data from one small-grain cereal to draw conclusions on other small-grain cereals.

Metabolo-transcriptome profiling of barley reveals induction of chitin elicitor receptor kinase gene (HvCERK1) conferring resistance against Fusarium graminearum

We report plausible disease resistance mechanisms induced by barley resistant genotype CI89831 against Fusarium head blight (FHB) based on metabolo-transcriptomics approach. We identified HvCERK1 as a candidate gene for FHB resistance, which is functional in resistant genotype CI9831 but non-functional in susceptible cultivars H106-371 and Zhedar-2. For the first time, we were able to show a hierarchy of regulatory genes that regulated downstream biosynthetic genes that eventually produced resistance related metabolites that reinforce the cell walls to contain the pathogen progress in plant. The HvCERK1 can be used for replacing in susceptible commercial cultivars, if non-functional, based on genome editing. Fusarium head blight (FHB) management is a great challenge in barley and wheat production worldwide. Though barley genome sequence and advanced omics technologies are available, till date none of the resistance mechanisms has been clearly deciphered. Hence, this study was aimed at identifying candidate gene(s) and elucidating resistance mechanisms induced by barley resistant genotype CI9831 based on integrated metabolomics and transcriptomics approach. Following Fusarium graminearum infection, we identified accumulation of specific set of induced secondary metabolites, belonging to phenylpropanoid, hydroxycinnamic acid (HCAA) and jasmonic acid pathways, and their biosynthetic genes. In association with these, receptor kinases such as chitin elicitor receptor kinase (HvCERK1) and protein kinases such as MAP kinase 3 (HvMPK3) and MAPK substrate 1 (HvMKS1), and transcription factors such as HvERF1/5, HvNAC42, HvWRKY23 and HvWRKY70 were also found upregulated with high fold change. Polymorphism studies across three barley genotypes confirmed the presence of mutations in HvCERK1 gene in two susceptible genotypes, isolating this gene as a potential candidate for FHB resistance. Further, the silencing of functional HvCERK1 gene in the resistant genotype CI9831, followed by gene expression and metabolite analysis revealed its role as an elicitor recognition receptor that triggered downstream regulatory genes, which in turn, regulated downstream metabolic pathway genes to biosynthesize resistance related (RR) metabolites to contain the pathogen to spikelet infection. A putative model on metabolic pathway regulation is proposed.

WAX INDUCER1 (HvWIN1) transcription factor regulates free fatty acid biosynthetic genes to reinforce cuticle to resist Fusarium head blight in barley spikelets

Fusarium head blight (FHB), caused by Fusarium graminearum, is one of the most devastating diseases of wheat and barley. Resistance to FHB is highly complex and quantitative in nature, and is most often classified as resistance to spikelet infection and resistance to spread of pathogen through the rachis. In the present study, a resistant (CI9831) and a susceptible (H106-371) two-row barley genotypes, with contrasting levels of spikelet resistance to FHB, pathogen or mock-inoculated, were profiled for metabolites based on liquid chromatography and high resolution mass spectrometry. The key resistance-related (RR) metabolites belonging to fatty acids, phenylpropanoids, flavonoids and terpenoid biosynthetic pathways were identified. The free fatty acids (FFAs) linoleic and palmitic acids were among the highest fold change RR induced (RRI) metabolites. These FFAs are deposited as cutin monomers and oligomers to reinforce the cuticle, which acts as a barrier to pathogen entry. Quantitative real-time PCR studies revealed higher expressions of KAS2, CYP86A2, CYP89A2, LACS2 and WAX INDUCER1 (HvWIN1) transcription factor in the pathogen-inoculated resistant genotype than in the susceptible genotype. Knockdown of HvWIN1 by virus-induced genes silencing (VIGS) in resistant genotype upon pathogen inoculation increased the disease severity and fungal biomass, and decreased the abundance of FFAs like linoleic and palmitic acids. Notably, the expression of CYP86A2, CYP89A2 and LAC2 genes was also suppressed, proving the link of HvWIN1 in regulating these genes in cuticle biosynthesis as a defense response.

Development and Genetic Characterization of an Advanced Backcross-Nested Association Mapping (AB-NAM) Population of Wild × Cultivated Barley

The ability to access alleles from unadapted germplasm collections is a long-standing problem for geneticists and breeders. Here we developed, characterized, and demonstrated the utility of a wild barley advanced backcross-nested association mapping (AB-NAM) population. We developed this population by backcrossing 25 wild barley accessions to the six-rowed malting barley cultivar Rasmusson. The 25 wild barley parents were selected from the 318 accession Wild Barley Diversity Collection (WBDC) to maximize allelic diversity. The resulting 796 BC2F4:6 lines were genotyped with 384 SNP markers, and an additional 4022 SNPs and 263,531 sequence variants were imputed onto the population using 9K iSelect SNP genotypes and exome capture sequence of the parents, respectively. On average, 96% of each wild parent was introgressed into the Rasmusson background, and the population exhibited low population structure. While linkage disequilibrium (LD) decay (r(2) = 0.2) was lowest in the WBDC (0.36 cM), the AB-NAM (9.2 cM) exhibited more rapid LD decay than comparable advanced backcross (28.6 cM) and recombinant inbred line (32.3 cM) populations. Three qualitative traits: glossy spike, glossy sheath, and black hull color were mapped with high resolution to loci corresponding to known barley mutants for these traits. Additionally, a total of 10 QTL were identified for grain protein content. The combination of low LD, negligible population structure, and high diversity in an adapted background make the AB-NAM an important tool for high-resolution gene mapping and discovery of novel allelic variation using wild barley germplasm.

Occurrence of 26 Mycotoxins in the Grain of Cereals Cultivated in Poland

The levels of 26 mycotoxins were determined in 147 samples of the grain of cereals cultivated in five regions of Poland during the 2014 growing season. The HPLC-HRMS (time-of-flight) analytical technique was used. An analytical procedure to simultaneously determine 26 mycotoxins in grain was developed, tested and verified. Samples from eastern and southern Poland were more contaminated with mycotoxins than the samples from northern and western Poland. Toxins produced by Fusarium fungi were the main contaminants found. Some deoxynivalenol (DON) was found in 100% of the tested samples of wheat (Osiny, Borusowa, Werbkowice), triticale, winter barley and oats, while the maximum permissible DON level (as defined in the EU Commission Regulation No. 1881/2006) was exceeded in 10 samples. Zearalenone (ZEN), DON metabolites and enniatins were also commonly found. The presence of mycotoxins in grain reflected the prevailing weather conditions during the plant flowering/earing stages, which were favorable for the development of blight. Among all investigated wheat genotypes, cv. Fidelius was the least contaminated, while Bamberka, Forkida and Kampana were the most contaminated. However, the single-factor ANOVA analysis of variance did not reveal (at a statistical significance level α = 0.05) any differences between levels of mycotoxins in individual genotypes. Triticale was the most contaminated grain among all of the tested varieties. ZEN, DON and the sum of 3-acetyldexynivalenol and 15-acetyldeoxynivalenol (3- and 15-ADON) were found in 100% of the tested triticale samples at concentrations within the 4-86, 196-1326 and 36-374 µg·kg(-1) range, respectively. Of particular concern was the fact that some "emerging mycotoxins" (enniatins) (in addition to commonly-known and legally-regulated mycotoxins) were also found in the tested triticale samples (enniatin B (Enn-B), enniatin B1 (Enn-B1), enniatin A-1 (Enn-A1), 100% of samples, and enniatin A (Enn-A), 70% of samples). Depending on the toxin, they were found at levels between 8 and 3328 µg·kg(-1).

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.

Colonisation of winter wheat grain by Fusarium spp. and mycotoxin content as dependent on a wheat variety, crop rotation, a crop management system and weather conditions

Field experiments were conducted during three consecutive growing seasons (2007/08, 2008/09 and 2009/10) with four winter wheat (Triticum aestivum L.) cultivars - 'Bogatka', 'Kris', 'Satyna' and 'Tonacja' - grown on fields with a three-field crop rotation (winter triticale, spring barley, winter wheat) and in a four-field crop rotation experiment (spring wheat, spring cereals, winter rapeseed, winter wheat). After the harvest, kernels were surface disinfected with 2% NaOCl and then analysed for the internal infection by different species of Fusarium. Fusaria were isolated on Czapek-Dox iprodione dichloran agar medium and identified on the basis of macro- and micro-morphology on potato dextrose agar and synthetic nutrient agar media. The total wheat grain infection by Fusarium depended mainly on relative humidity (RH) and a rainfall during the flowering stage. Intensive rainfall and high RH in 2009 and 2010 in the period meant the proportions of infected kernels by the fungi were much higher than those in 2008 (lack of precipitation during anthesis). Weather conditions during the post-anthesis period changed the species composition of Fusarium communities internally colonising winter wheat grain. The cultivars significantly varied in the proportion of infected kernels by Fusarium spp. The growing season and type of crop rotation had a distinct effect on species composition of Fusarium communities colonising the grain inside. A trend of a higher percentage of the colonised kernels by the fungi in the grain from the systems using more fertilisers and pesticides as well as the buried straw could be perceived. The most frequent species in the grain were F. avenaceum, F. tricinctum and F. poae in 2008, and F. avenaceum, F. graminearum, F. tricinctum and F. poae in 2009 and 2010. The contents of deoxynivalenol and zearalenon in the grain were correlated with the percentage of kernels colonised by F. graminearum and were the highest in 2009 in the grain from the four-field crop rotation. The content of T-2/HT-2 toxins was the highest in 2010 in grain from the three-field crop rotation and it was correlated with the isolation frequency of F. langsethiae.

Novel septoria speckled leaf blotch resistance loci in a barley doubled-haploid population

The genetics of resistance to Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii, was studied in the Leger × CIho9831 barley doubled-haploid population. The 140 lines in the population segregated as 102 resistant and 38 susceptible, approximating a 3:1 ratio. A recombination map was developed using diversity arrays technology and other molecular markers. Quantitative trait locus (QTL) analysis demonstrated that resistance is primarily conferred either by having the CIho9831 allele at a QTL on 6HS or by having the CIho9831 allele at both of two QTLs on 3H and 2HL. In addition, ≈1/16 of the lines were resistant for unidentified reasons. This model predicts a resistant/susceptible ratio of 11:5, which fits the phenotypic observations. Minor QTLs were detected on 2HS and 1H. DNA sequences of linked markers suggest that the 6HS, 3H, and 2HS QTLs are part of resistance gene clusters and that the 6HS and 3H QTLs share homology. The 6HS QTL is identical to or closely linked to the SSLB resistance locus Rsp4 and the 1H QTL to the Rsp2 or Rsp3 locus. The 3H and 2HS QTLs are unique and offer new opportunities for pyramiding resistance genes through marker-assisted breeding for resistance to S. passerinii.

Resistance to Fusarium Head Blight and Deoxynivalenol Accumulation in Virginia Barley

Fusarium graminearum (teleomorph Gibberella zeae), is a devastating disease of barley (Hordeum vulgare) in the United States. Recent epidemics of FHB in the mid-Atlantic region have underscored the need to develop new commercial varieties of barley that are resistant to FHB and restrict accumulation of the mycotoxin deoxynivalenol (DON). FHB incidence, FHB index, and DON levels of Virginia hulled and hulless barley genotypes were evaluated over five years (2006 to 2010) in FHB nurseries in Virginia. FHB incidence ranged from 22.5% (2010) to 80.1% (2008), and mean DON levels ranged from 0.5 ± 0.4 (2008) to 2.4 ± 2.1 ppm (2010). Barley genotype played a significant role in determining FHB resistance in 2006 to 2009. DON levels were significantly different among barley genotypes in 2007, 2008, and 2009. FHB incidence was positively correlated with FHB index in all 5 years studied. In 2006 and 2010, FHB incidence and index were positively correlated with DON. Early spike emergence resulted in higher FHB incidence and index in 2007, 2008, and 2010. This preliminary work has identified some promising hulled and hulless barley genotypes for targeted breeding and commercialization efforts in FHB nurseries in the future; 'Eve' (hulless) and 'Thoroughbred' (hulled) ranked among the most FHB resistant genotypes.

Transcriptome analysis of trichothecene-induced gene expression in barley

Fusarium head blight, caused primarily by Fusarium graminearum, is a major disease problem on barley (Hordeum vulgare L.). Trichothecene mycotoxins produced by the fungus during infection increase the aggressiveness of the fungus and promote infection in wheat (Triticum aestivum L.). Loss-of-function mutations in the TRI5 gene in F. graminearum result in the inability to synthesize trichothecenes and in reduced virulence on wheat. We examined the impact of pathogen-derived trichothecenes on virulence and the transcriptional differences in barley spikes infected with a trichothecene-producing wild-type strain and a loss-of-function tri5 trichothecene nonproducing mutant. Disease severity, fungal biomass, and floret necrosis and bleaching were reduced in spikes inoculated with the tri5 mutant strain compared with the wild-type strain, indicating that the inability to synthesize trichothecenes results in reduced virulence in barley. We detected 63 transcripts that were induced during trichothecene accumulation, including genes encoding putative trichothecene detoxification and transport proteins, ubiquitination-related proteins, programmed cell death-related proteins, transcription factors, and cytochrome P450s. We also detected 414 gene transcripts that were designated as basal defense response genes largely independent of trichothecene accumulation. Our results show that barley exhibits a specific response to trichothecene accumulation that can be separated from the basal defense response. We propose that barley responds to trichothecene accumulation by inducing at least two general responses. One response is the induction of genes encoding trichothecene detoxification and transport activities that may reduce the impact of trichothecenes. The other response is to induce genes encoding proteins associated with ubiquitination and cell death which may promote successful establishment of the disease.