Salicylic acid regulates basal resistance to Fusarium head blight in wheat

Fusarium head blight (FHB) is a destructive disease of cereal crops such as wheat and barley. Previously, expression in wheat of the Arabidopsis NPR1 gene (AtNPR1), which encodes a key regulator of salicylic acid (SA) signaling, was shown to reduce severity of FHB caused by Fusarium graminearum. It was hypothesized that SA signaling contributes to wheat defense against F. graminearum. Here, we show that increased accumulation of SA in fungus-infected spikes correlated with elevated expression of the SA-inducible pathogenesis-related 1 (PR1) gene and FHB resistance. In addition, FHB severity and mycotoxin accumulation were curtailed in wheat plants treated with SA and in AtNPR1 wheat, which is hyper-responsive to SA. In support of a critical role for SA in basal resistance to FHB, disease severity was higher in wheat expressing the NahG-encoded salicylate hydroxylase, which metabolizes SA. The FHB-promoting effect of NahG was overcome by application of benzo (1,2,3), thiadiazole-7 carbothioic acid S-methyl ester, a synthetic functional analog of SA, thus confirming an important role for SA signaling in basal resistance to FHB. We further demonstrate that jasmonate signaling has a dichotomous role in wheat interaction with F. graminearum, constraining activation of SA signaling during early stages of infection and promoting resistance during the later stages of infection.     

Comparison of the efficacy of chitosan with that of a fluorescent pseudomonad for the control of Fusarium head blight disease of cereals and associated mycotoxin contamination of grain

Fusarium culmorum can cause Fusarium head blight (FHB) disease of cereals, resulting in yield loss and contamination of grain with the trichothecene mycotoxin, deoxynivalenol (DON). In this study, we compared the efficacy of a biological control agent (Pseudomonas fluorescens strain MKB 158) with the biochemical chitosan (the deacetylated derivative of chitin) in controlling FHB disease of wheat and barley. Both agents were equally effective in reducing DON contamination of grain caused by F. culmorum. Under both glasshouse and field conditions, treatment with commercially available crabshell-derived chitosan reduced the severity of FHB symptom development on wheat and barley by ?74% (P ? 0.050). While treatment with P. fluorescens reduced the severity of FHB symptom development on these cereals by ?48% (P ? 0.050). Chitosan and P. fluorescens respectively prevented ?58 and ?35% of the FHB-associated reductions in 1000-grain weight in wheat and barley (P ? 0.050). Both agents significantly reduced the DON content of wheat and barley under both glasshouse and field conditions (P ? 0.050) and were equally efficacious in doing so (?74 and ?79% reductions due to chitosan and P. fluorescens, respectively). Crude chitin extracts from crabshells and crude chitosan-based formulations prepared from crabshells and eggshells were also tested under field conditions, but were not as effective as the commercial crabshell-derived preparation in controlling FHB disease. This is the first report on the use of chitosan for the control of Fusarium head blight disease and DON contamination of grain.     

Recognition of glycoside hydrolase 12 proteins by the immune receptor RXEG1 confers Fusarium head blight resistance in wheat

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease in wheat (Triticum aestivum) that results in substantial yield losses and mycotoxin contamination. Reliable genetic resources for FHB resistance in wheat are lacking. In this study, we characterized glycoside hydrolase 12 (GH12) family proteins secreted by F. graminearum. We established that two GH12 proteins, Fg05851 and Fg11037, have functionally redundant roles in F. graminearum colonization of wheat. Furthermore, we determined that the GH12 proteins Fg05851 and Fg11037 are recognized by the leucine-rich-repeat receptor-like protein RXEG1 in the dicot Nicotiana benthamiana. Heterologous expression of RXEG1 conferred wheat responsiveness to Fg05851 and Fg11037, enhanced wheat resistance to F. graminearum and reduced levels of the mycotoxin deoxynivalenol in wheat grains in an Fg05851/Fg11037-dependent manner. In the RXEG1 transgenic lines, genes related to pattern-triggered plant immunity, salicylic acid, jasmonic acid, and anti-oxidative homeostasis signalling pathways were upregulated during F. graminearum infection. However, the expression of these genes was not significantly changed during infection by the deletion mutant ΔFg05851/Fg11037, suggesting that the recognition of Fg05851/Fg11037 by RXEG1 triggered plant resistance against FHB. Moreover, introducing RXEG1 into three other different wheat cultivars via crossing also conferred resistance to F. graminearum. Expression of RXEG1 did not have obvious deleterious effects on plant growth and development in wheat. Our study reveals that N. benthamiana RXEG1 remains effective when transferred into wheat, a monocot, which in turn suggests that engineering wheat with interfamily plant immune receptor transgenes is a viable strategy for increasing resistance to FHB.     

Identification of a UDP-glucosyltransferase conferring deoxynivalenol resistance in Aegilops tauschii and wheat

Aegilops tauschii is the diploid progenitor of the wheat D subgenome and a valuable resource for wheat breeding, yet, genetic analysis of resistance against Fusarium head blight (FHB) and the major Fusarium mycotoxin deoxynivalenol (DON) is lacking. We treated a panel of 147 Ae. tauschii accessions with either Fusarium graminearum spores or DON solution and recorded the associated disease spread or toxin-induced bleaching. A k-mer-based association mapping pipeline dissected the genetic basis of resistance and identified candidate genes. After DON infiltration nine accessions revealed severe bleaching symptoms concomitant with lower conversion rates of DON into the non-toxic DON-3-O-glucoside. We identified the gene AET5Gv20385300 on chromosome 5D encoding a uridine diphosphate (UDP)-glucosyltransferase (UGT) as the causal variant and the mutant allele resulting in a truncated protein was only found in the nine susceptible accessions. This UGT is also polymorphic in hexaploid wheat and when expressed in Saccharomyces cerevisiae only the full-length gene conferred resistance against DON. Analysing the D subgenome helped to elucidate the genetic control of FHB resistance and identified a UGT involved in DON detoxification in Ae. tauschii and hexaploid wheat. This resistance mechanism is highly conserved since the UGT is orthologous to the barley UGT HvUGT13248 indicating descent from a common ancestor of wheat and barley.     

Simultaneous detection of Fusarium asiaticum and Fusarium graminearum in wheat seeds using a real-time PCR method

Aims:  To develop a PCR-based method for quantitative detection of Fusarium asiaticum ( Fa ) and Fusarium graminearum ( Fg ) in wheat seeds.
Methods and Results:  Based on the sequences of the cyp51A gene, two primer pairs FaF + FaR and FgF + FgR were developed for the species-specific detection of Fa and Fg , respectively. To simultaneously detect these two phylogenetic species, a pair of primers FgaF + FgaR was developed based on the first and the second introns of β -tubulin gene. This primer pair amplified a 228-bp fragment only from Fa and Fg isolates, but not from 22 other Fusarium spp. and 13 other fungal species. A real-time PCR with this primer pair was able to quantify minute amounts of Fa and Fg DNA in wheat seeds rapidly.
Conclusions:  PCR primers designed based on the sequence of cyp51A or intron region of β -tubulin gene could allow differentiation of genetically related fungal species.
Significance and Impact of the Study:  The sensitive and quantitative detection method can be readily used in epidemiological studies and in assessing risk of Fusarium mycotoxin contamination in wheat samples.     

Haplotype diversity and population structure in cultivated and wild barley evaluated for Fusarium head blight responses

Fusarium head blight (FHB) is a threat to barley (Hordeum vulgare L.) production in many parts of the world. A number of barley accessions with partial resistance have been reported and used in mapping experiments to identify quantitative trait loci (QTL) associated with FHB resistance. Here, we present a set of barley germplasm that exhibits FHB resistance identified through screening a global collection of 23,255 wild (Hordeum vulgare ssp. spontaneum) and cultivated (Hordeum vulgare ssp. vulgare) accessions. Seventy-eight accessions were classified as resistant or moderately resistant. The collection of FHB resistant accessions consists of 5, 27, 46 of winter, wild and spring barley, respectively. The population structure and genetic relationships of the germplasm were investigated with 1,727 Diversity Array Technology (DArT) markers. Multiple clustering analyses suggest the presence of four subpopulations. Within cultivated barley, substructure is largely centered on spike morphology and growth habit. Analysis of molecular variance indicated highly significant genetic variance among clusters and within clusters, suggesting that the FHB resistant sources have broad genetic diversity. The haplotype diversity was characterized with DArT markers associated with the four FHB QTLs on chromosome 2H bin8, 10 and 13 and 6H bin7. In general, the wild barley accessions had distinct haplotypes from those of cultivated barley. The haplotype of the resistant source Chevron was the most prevalent in all four QTL regions, followed by those of the resistant sources Fredrickson and CIho4196. These resistant QTL haplotypes were rare in the susceptible cultivars and accessions grown in the upper Midwest USA. Some two- and six-rowed accessions were identified with high FHB resistance, but contained distinct haplotypes at FHB QTLs from known resistance sources. These germplasm warrant further genetic studies and possible incorporation into barley breeding programs.     

Identification and Genetic Division of Fusarium graminearum and Fusarium asiaticum by Species‐Specific SCAR Markers

Fusarium head blight (FHB), also called scab, is a devastating and insidious disease of cereals including wheat (Triticum spp.) and barley (Hordeum vulgare L.) worldwide. Apart from direct yield losses, the most serious concern about FHB is the contamination of the crop with mycotoxins, which pose a health risk to human and livestock. Recent research reported that phylogenetic species F. asiaticum (Fa) and F. graminearum (Fg) were the major causal agents of FHB from infected wheat heads in China. To investigate the population structure of Fusarium species in China by species‐specific as well as the chemotype‐specific markers, sequence‐related amplified polymorphism (SRAP) markers were screened on representative isolates of F. asiaticum‐NIV, F. asiaticum‐ 3ADON and F. graminearum‐15ADON to find amplification products characteristic of either species or chemotypes. Selected amplified fragments were cloned and sequenced so that sequence‐characterized amplified region (SCAR) primer pairs could be developed which permit specific detection of Fusarium species using conventional PCR. Primer pairs SCAR‐Fa1 and SCAR‐Fg1 were confirmed to be able to amplify specific products only in F. asiaticum and F. graminearum isolates, respectively. These species‐specific primers were applied to determine genetic division of F. asiaticum and F. graminearum isolates collected in Yangtze–Huaihe valley. The results indicated that F. asiaticum was the predominant species causing FHB in this wheat production area. It is the first report that SRAP markers were adapted for species characterization in Fusarium isolates.     

Overexpression of defense response genes in transgenic wheat enhances resistance to Fusarium head blight

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum and other Fusarium species, is a major disease problem for wheat production worldwide. To combat this problem, large-scale breeding efforts have been established. Although progress has been made through standard breeding approaches, the level of resistance attained is insufficient to withstand epidemic conditions. Genetic engineering provides an alternative approach to enhance the level of resistance. Many defense response genes are induced in wheat during F. graminearum infection and may play a role in reducing FHB. The objectives of this study were (1) to develop transgenic wheat overexpressing the defense response genes α-1-purothionin, thaumatin-like protein 1 (tlp-1), and β-1,3-glucanase; and (2) to test the resultant transgenic wheat lines against F. graminearum infection under greenhouse and field conditions. Using the wheat cultivar Bobwhite, we developed one, two, and four lines carrying the α-1-purothionin, tlp-1, and β-1,3-glucanase transgenes, respectively, that had statistically significant reductions in FHB severity in greenhouse evaluations. We tested these seven transgenic lines under field conditions for percent FHB disease severity, deoxynivalenol (DON) mycotoxin accumulation, and percent visually scabby kernels (VSK). Six of the seven lines differed from the nontransgenic parental Bobwhite line for at least one of the disease traits. A β-1,3-glucanase transgenic line had enhanced resistance, showing lower FHB severity, DON concentration, and percent VSK compared to Bobwhite. Taken together, the results showed that overexpression of defense response genes in wheat could enhance the FHB resistance in both greenhouse and field conditions.     

Response to Fusarium culmorum inoculation in barley

In field tests replicated in 2004 and 2005, 32 cultivars of spring barley were assessed for resistance to Fusarium head blight (FHB) by single floret inoculation and spray inoculation with Fusarium culmorum (W. G. Smith) Sacc. It was found that the weather conditions in individual years affect to a large extent the progression of FHB and production of mycotoxin deoxynivalenol (DON). At the same time, in both years the cultivars reacted to F. culmorum infection similarly with respect to areas under disease progress curve (AUDPC) values and content of mycotoxin DON. Spraying inoculation led to stronger infection. The biggest differences in AUDPC values were observed between the cultivars Brise and Celinka, and weak reaction was found in the cultivars Kompakt and Madonna. The cultivars Kompakt and Tolar were most resistant towards FHB. In both monitored years the variety Ludan contained the lowest amounts of mycotoxin DON. Cultivars with high infection and low DON content (r = 0.78) showed weak positive relationship between resistance to FBH and accumulation of DON (concentration 70–200 mg/kg). This is the first information on FHB and in vivo concentrations of DON in certificated barley cultivars in Slovakia.     

Simultaneous detection of Fusarium culmorum and F. graminearum in plant material by duplex PCR with melting curve analysis

Background  

Fusarium head blight (FHB) is a disease of cereal crops, which has a severe impact on wheat and barley production worldwide. Apart from reducing the yield and impairing grain quality, FHB leads to contamination of grain with toxic secondary metabolites (mycotoxins), which pose a health risk to humans and livestock. The Fusarium species primarily involved in FHB are F. graminearum and F. culmorum. A key prerequisite for a reduction in the incidence of FHB is an understanding of its epidemiology.     

Transgenic wheat expressing a barley class II chitinase gene has enhanced resistance against Fusarium graminearum

Fusarium head blight (FHB; scab), primarily caused by Fusarium graminearum, is a devastating disease of wheat worldwide. FHB causes yield reductions and contamination of grains with trichothecene mycotoxins such as deoxynivalenol (DON). The genetic variation in existing wheat germplasm pools for FHB resistance is low and may not provide sufficient resistance to develop cultivars through traditional breeding approaches. Thus, genetic engineering provides an additional approach to enhance FHB resistance. The objectives of this study were to develop transgenic wheat expressing a barley class II chitinase and to test the transgenic lines against F. graminearum infection under greenhouse and field conditions. A barley class II chitinase gene was introduced into the spring wheat cultivar, Bobwhite, by biolistic bombardment. Seven transgenic lines were identified that expressed the chitinase transgene and exhibited enhanced Type II resistance in the greenhouse evaluations. These seven transgenic lines were tested under field conditions for percentage FHB severity, percentage visually scabby kernels (VSK), and DON accumulation. Two lines (C8 and C17) that exhibited high chitinase protein levels also showed reduced FHB severity and VSK compared to Bobwhite. One of the lines (C8) also exhibited reduced DON concentration compared with Bobwhite. These results showed that transgenic wheat expressing a barley class II chitinase exhibited enhanced resistance against F. graminearum in greenhouse and field conditions.     

Multilocus genotyping and molecular phylogenetics resolve a novel head blight pathogen within the Fusarium graminearum species complex from Ethiopia

A survey of Fusarium head blight (FHB)-contaminated wheat in Ethiopia recovered 31 isolates resembling members of the Fusarium graminearum species complex. Results of a multilocus genotyping (MLGT) assay for FHB species and trichothecene chemotype determination suggested that 22 of these isolates might represent a new species within the Fg complex. Phylogenetic analyses of multilocus DNA sequence data resolved the 22 Ethiopian isolates as a novel, phylogenetically distinct species. The new species also appears to be novel in that MLGT probe data and sequence analysis of both ends of the TRI-cluster identified 15ADON and NIV recombination blocks, documenting inter-chemotype recombination involving the chemotype-determining genes near the ends of the TRI-cluster. Results of pathogenicity experiments and analyses of trichothecene mycotoxins demonstrated that this novel Fg complex species could induce FHB on wheat and elaborate 15ADON in planta. Herein the FHB pathogen from Ethiopia is formally described as a novel species.     

Transgenic expression of polygalacturonase-inhibiting proteins in Arabidopsis and wheat increases resistance to the flower pathogen Fusarium graminearum

Fusarium head blight (FHB), caused by Fusarium graminearum, is one of the most important diseases of wheat worldwide, resulting in yield losses and mycotoxin contamination. The molecular mechanisms regulating Fusarium penetration and infection are poorly understood. Beside mycotoxin production, cell wall degradation may play a role in the development of FHB. Many fungal pathogens secrete polygalacturonases (PGs) during the early stages of infection, and plants have evolved polygalacturonase-inhibiting proteins (PGIPs) to restrict pectin degradation during fungal infection. To investigate the role of plant PGIPs in restricting the development of FHB symptoms, we first used Arabidopsis thaliana, whose genome encodes two PGIPs (AtPGIP1 and AtPGIP2). Arabidopsis transgenic plants expressing either of these PGIPs under control of the CaMV 35S promoter accumulate inhibitory activity against F.?graminearum PG in their inflorescences, and show increased resistance to FHB. Second, transgenic wheat plants expressing the bean PvPGIP2 in their flowers also had a significant reduction of symptoms when infected with F.?graminearum. Our data suggest that PGs likely play a role in F.?graminearum infection of floral tissues, and that PGIPs incorporated into wheat may be important for increased resistance to FHB.     

Selection and evaluation of the potential of choline-metabolizing microbial strains to reduce Fusarium head blight

Choline and betaine are found in wheat flower tissues and have been implicated in stimulating hyphal growth of the primary causal agent of Fusarium head blight (FHB), Gibberella zeae. Choline metabolizing strains (CMS) from wheat anthers may therefore be a useful source of antagonists of G. zeae. One-hundred twenty-three of 738 microbial strains that were recovered from wheat anthers collected from plants grown in Illinois and Ohio were CMS as determined by growth in a liquid medium containing choline as a sole carbon and nitrogen source and a colorimetric, choline oxidase-based assay of culture filtrate. Thirty-one out of 123 CMS reduced FHB disease severity by at least 25% in greenhouse tests on wheat and 17 reduced FHB severity by at least 50%. All five CMS selected for field testing in 2003 reduced disease severity compared to the untreated check at both field locations on moderately resistant cultivar Freedom. Freedom wheat treated with Pseudomonas sp. AS 64.4 had 63% and 46% less FHB severity than untreated wheat at the two sites. Three of five CMS reduced severity at both locations on susceptible cultivar Pioneer Brand 2545. Disease control was comparable to that obtained using the fungicide Folicur 3.6F. Selection of wheat anther colonists for ability to utilize choline as a sole carbon and nitrogen source has utility as a screening tool in the search for efficacious antagonists of G. zeae although choline utilization does not insure that an isolate will be an effective biocontrol agent against Fusarium head blight.     

Sanitary factors and mycotoxin contamination in the argentinian wheat crop 1993/94

In Argentina, due to climatic conditions, Fusarium head blight (FHB) caused by Fusarium graminearum, affected the 1993/94 wheat crop. To evaluate the severity of this disease, samples of wheat where gathered from four zones of the wheat area. Sanitary conditions and mycotoxin contamination were determined. One zone (IIN) was intensely affected by FHB with 90% of samples in grade III (bad quality). No samples were grade I (good quality). The other zones were less affected falling into grade I or II (moderate quality). In all samples tested F. graminearum was the most prevalent species singly or in combination with others. Zone II N, with a DON mean level of I1.26 ppm, did not fulfil aceptability limits, whereas zones IIS, III and IV with overall means of 2.12, 1.57 and 1.0 ppm, respectively, did. Statistical analysis showed a close relation between percentage FHB and DON contamination (r:-0.71, p<0.01) in infected samples.     

Comparative Mycotoxin Profiles of Gibberella zeae Populations from Barley, Wheat, Potatoes, and Sugar Beets

Gibberella zeae is one of the most devastating pathogens of barley and wheat in the United States. The fungus also infects noncereal crops, such as potatoes and sugar beets, and the genetic relationships among barley, wheat, potato, and sugar beet isolates indicate high levels of similarity. However, little is known about the toxigenic potential of G. zeae isolates from potatoes and sugar beets. A total of 336 isolates of G. zeae from barley, wheat, potatoes, and sugar beets were collected and analyzed by TRI (trichothecene biosynthesis gene)-based PCR assays. To verify the TRI-based PCR detection of genetic markers by chemical analysis, 45 representative isolates were grown in rice cultures for 28 days and 15 trichothecenes and 2 zearalenone (ZEA) analogs were quantified using gas chromatography-mass spectrometry. TRI-based PCR assays revealed that all isolates had the deoxynivalenol (DON) marker. The frequencies of isolates with the 15-acetyl-deoxynivalenol (15-ADON) marker were higher than those of isolates with the 3-acetyl-deoxynivalenol (3-ADON) marker among isolates from all four crops. Fusarium head blight (FHB)-resistant wheat cultivars had little or no influence on the diversity of isolates associated with the 3-ADON and 15-ADON markers. However, the frequency of isolates with the 3-ADON marker among isolates from the Langdon, ND, sampling site was higher than those among isolates from the Carrington and Minot, ND, sites. In chemical analyses, DON, 3-ADON, 15-ADON, b-ZEA, and ZEA were detected. All isolates produced DON (1 to 782 μg/g) and ZEA (1 to 623 μg/g). These findings may be useful for monitoring mycotoxin contamination and for formulating FHB management strategies for these crops.     

Identification of QTLs associated with Fusarium head blight resistance in Zhedar 2 barley

Fusarium head blight (FHB) in barley and wheat, caused by Fusarium graminearum, is a continual problem worldwide. Primarily, FHB reduces yield and quality, and results in the production of the toxin deoxynivalenol (DON), which can affect food safety. Identification of QTLs for FHB severity, DON level and related traits heading-date (HD) and plant-height (HT) with consistent effects across a set of environments, would provide the basis for marker-assisted selection (MAS) and potentially increase the efficiency of selection for resistance. A segregating population of 75 double-haploid lines, developed from the three-way cross Zhedar 2/ND9712//Foster, was used for genome mapping and FHB severity evaluation. A linkage map of 214 RFLP, SSR and AFLP markers was constructed. Phenotypic data were collected in replicated field trials from five environments in two growing seasons. The data were analyzed using MQTL software to detect quantitative trait locus (QTL) × environment (E) interactions. Because of the presence of QTL × E, the MQM procedure in MAPQTL was applied to identify QTLs in single environments. We identified nine QTLs for FHB severity and five for low DON. Many of the disease-related QTLs identified were coincident with FHB QTLs identified in previous studies. Only two of the QTLs identified in this study were consistent across all five environments, and both were Zhedar 2 specific. Five of the FHB QTLs were associated with HD, and two were associated with HT. Regions that appear to be promising candidates for MAS and further genetic analysis include the two FHB QTLs on chromosome 2H and one on 6H, which were also associated with low DON and later heading-date in multiple environments. This study provides a starting point for manipulating Zhedar 2-derived resistance by MAS in barley to develop cultivars that will show effective resistance under disease pressure.Communicated by H.F. Linskens     

Does function follow form? Principal QTLs for Fusarium head blight (FHB) resistance are coincident with QTLs for inflorescence traits and plant height in a doubled-haploid population of barley

Fusarium head blight (FHB), an important disease of barley in many areas of the world, causes losses in grain yield and quality. Deoxynivalenol (DON) mycotoxin residues, produced by the primary pathogen Fusarium graminearum, pose potential health risks. Barley producers may not be able to profitably market FHB-infected barley, even though it has a low DON level. Three types of FHB resistance have been described in wheat: Type I (penetration), Type II (spread), and Type III (mycotoxin degradation). We describe putative measures of these three types of resistance in barley. In wheat, the three resistance mechanisms show quantitative inheritance. Accordingly, to study FHB resistance in barley, we used quantitative trait locus (QTL) mapping to determine the number, genome location, and effects of QTLs associated with Type-I and -II resistance and the concentration of DON in the grain. We also mapped QTLs for plant height, heading date, and morphological attributes of the inflorescence (seeds per inflorescence, inflorescence density, and lateral floret size). QTL analyses were based on a mapping population of F₁-derived doubled-haploid (DH) lines from the cross of the two-rowed genotypes Gobernadora and CMB643, a linkage map constructed with RFLP marker loci, and field evaluations of the three types of FHB resistance performed in China, Mexico, and two environments in North Dakota, USA. Resistance QTLs were detected in six of the seven linkage groups. Alternate favorable alleles were found at the same loci when different inoculation techniques were used to measure Type-I resistance. The largest-effect resistance QTL (for Type-II resistance) was mapped in the centromeric region of chromosome 2. All but two of the resistance QTLs coincided with QTLs determining morphological attributes of the inflorescence and/or plant height. Additional experiments are needed to determine if these coincident QTLs are due to linkage or pleiotropy and to more clearly define the biological basis of the FHB resistance QTLs. Plant architecture should be considered in FHB resistance breeding efforts, particularly those directed at resistance QTL introgression and/or pyramiding. Received: 22 November 1998 / Accepted: 2 June 1999     

Response of Barley Genotypes to Fusarium Head Blight under Natural Infection and Artificial Inoculation Conditions

Forty-eight spring barley genotypes were evaluated for deoxynivalenol (DON) concentration under natural infection across 5 years at Harrington, Prince Edward Island. These genotypes were also evaluated for Fusarium head blight (FHB) severity and DON concentration under field nurseries with artificial inoculation of Fusarium graminearum by the grain spawn method across 2 years at Ottawa, Ontario, and one year at Hangzhou, China. Additionally, these genotypes were also evaluated for FHB severity under greenhouse conditions with artificial inoculation of F. graminearum by conidial suspension spray method across 3 years at Ottawa, Ontario. The objective of the study was to investigate if reactions of barley genotypes to artificial FHB inoculation correlate with reactions to natural FHB infection. DON concentration under natural infection was positively correlated with DON concentration (r = 0.47, P < 0.01) and FHB incidence (r = 0.56, P < 0.01) in the artificially inoculated nursery with grain spawn method. Therefore, the grain spawn method can be used to effectively screen for low DON. FHB severity, generated from greenhouse spray, however, was not correlated with DON concentration (r = 0.12, P > 0.05) under natural infection and it was not correlated with DON concentration (r = −0.23, P > 0.05) and FHB incidence (r = 0.19, P > 0.05) in the artificially inoculated nursery with grain spawn method. FHB severity, DON concentration, and yield were affected by year, genotype, and the genotype × year interaction. The effectiveness of greenhouse spray inoculation for indirect selection for low DON concentration requires further studies. Nine of the 48 genotypes were found to contain low DON under natural infection. Island barley had low DON and also had high yield.