Effect of individual Sumai 3 chromosomes on resistance to scab spread within spikes and deoxynivalenol accumulation within kernels in wheat

Mapping Resistance to Argentinean Fusarium (Graminearum) Head Blight Isolates in Wheat

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum (Schwabe), is a destructive disease worldwide, reducing wheat yield and quality. To accelerate the improvement of scab tolerance in wheat, we assessed the International Triticeae Mapping Initiative mapping population (ITMI/MP) for Type I and II resistance against a wide population of Argentinean isolates of F. graminearum. We discovered a total of 27 additive QTLs on ten different (2A, 2D, 3B, 3D, 4B, 4D, 5A, 5B, 5D and 6D) wheat chromosomes for Type I and Type II resistances explaining a maximum of 15.99% variation. Another four and two QTLs for thousand kernel weight in control and for Type II resistance, respectively, involved five different chromosomes (1B, 2D, 6A, 6D and 7D). Furthermore, three, three and five QTLs for kernel weight per spike in control, for Type I resistance and for Type II resistance, correspondingly, involved ten chromosomes (2A, 2D, 3B, 4A, 5A, 5B, 6B, 7A, 7B, 7D). We were also able to detect five and two epistasis pairs of QTLs for Type I and Type II resistance, respectively, in addition to additive QTLs that evidenced that FHB resistance in wheat is controlled by a complex network of additive and epistasis QTLs.

Mapping of Major Fusarium Head Blight Resistance from Canadian Wheat cv. AAC Tenacious

Fusarium head blight (FHB) is one of the most devastating wheat disease due to its direct detrimental effects on grain-yield, quality and marketability. Resistant cultivars offer the most effective approach to manage FHB; however, the lack of different resistance resources is still a major bottleneck for wheat breeding programs. To identify and dissect FHB resistance, a doubled haploid wheat population produced from the Canadian spring wheat cvs AAC Innova and AAC Tenacious was phenotyped for FHB response variables incidence and severity, visual rating index (VRI), deoxynivalenol (DON) content, and agronomic traits days to anthesis (DTA) and plant height (PHT), followed by single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) marker genotyping. A high-density map was constructed consisting of 10,328 markers, mapped on all 21 chromosomes with a map density of 0.35 cM/marker. Together, two major quantitative trait loci for FHB resistance were identified on chromosome 2D from AAC Tenacious; one of these loci on 2DS also colocated with loci for DTA and PHT. Another major locus for PHT, which cosegregates with locus for low DON, was also identified along with many minor and epistatic loci. QTL identified from AAC Tenacious may be useful to pyramid FHB resistance.

WFhb1-1 plays an important role in resistance against Fusarium head blight in wheat

Fusarium head blight (FHB) is a severe disease of wheat (Triticum aestivum L.). Qfhb1 is the most important quantitative trait locus (QTL) for FHB resistance. We previously identified wheat gene WFhb1-1 (aka WFhb1-c1) as a candidate for FHB resistance gene. Here we report that WFhb1-1 has been cloned. The gene (GenBank # KU304333.1) consists of a single exon, encoding a putative membrane protein of 127 amino acids. WFhb1-1 protein produced in Pichia pastoris inhibits growth of both F. graminearum and P. pastoris in culture. Western Blotting with anti- WFhb1-1 antibody revealed a significant decrease (p < 0.01) in WFhb1-1 accumulation, 12 hours post Fusarium inoculation in non-Qfhb1-carrier wheat but not in Qfhb1-carrier wheat. Overexpressing WFhb1-1 in non-Qfhb1-carrier wheat led to a significant decrease (p < 0.01) in Fusarium-damaged rachis rate, Fusarium-diseased kernel rate and DON content in harvested kernels, while silencing WFhb1-1 in Qfhb1-carrier wheat resulted in a significant increase (p < 0.01) in FHB severity. Therefore, WFhb1-1 is an important FHB resistance gene with a potential antifungal function and probably a key functional component of Qfhb1 in wheat. A model regarding how WFhb1-1 functions in FHB resistance/susceptibility is hypothesized and discussed.

Genetic factors affecting Fusarium head blight resistance improvement from introgression of exotic Sumai 3 alleles (including Fhb1, Fhb2, and Fhb5) in hard red spring wheat

BACKGROUND

Fusarium head blight resistance genes, Fhb1 (for Type-II resistance), Fhb2 (Type-II), and Fhb5 (Type-I plus some Type-II), which originate from Sumai 3, are among the most important that confer resistance in hexaploid wheat. Near-isogenic lines (NILs), in the CDC Alsask (susceptible; n = 32) and CDC Go (moderately susceptible; n = 38) backgrounds, carrying these genes in all possible combinations were developed using flanking microsatellite markers and evaluated for their response to FHB and deoxynivalenol (DON) accumulation in eight environments. NILs were haplotyped with wheat 90 K iSelect assay to elucidate the genomic composition and confirm alleles' presence. Other than evaluating the effects of three major genes in common genetic background, the study elucidated the epistatic gene interactions as they influence FHB measurements; identified loci other than Fhb1, Fhb2, and Fhb5, in both recurrent and donor parents and examined annotated proteins in gene intervals.

RESULTS

Genotyping using 81,857 single nucleotide polymorphism (SNP) markers revealed polymorphism on all chromosomes and that the NILs carried < 3% of alleles from the resistant donor. Significant improvement in field resistance (Type-I + Type-II) resulted only among the CDC Alsask NILs, not the CDC Go NILs. The phenotypic response of NILs carrying combinations of Sumai 3 derived genes suggested non-additive responses and Fhb5 was as good as Fhb1 in conferring field resistance in both populations. In addition to Fhb1, Fhb2, and Fhb5, four to five resistance improving alleles in both populations were identified and three of five in CDC Go were contributed by the susceptible parent. The introgressed chromosome regions carried genes encoding disease resistance proteins, protein kinases, nucleotide-binding and leucine rich repeats' domains. Complex epistatic gene-gene interactions among marker loci (including Fhb1, Fhb2, Fhb5) explained > 20% of the phenotypic variation in FHB measurements.

CONCLUSIONS

Immediate Sumai 3 derivatives carry a number of resistance improving minor effect alleles, other than Fhb1, Fhb2, Fhb5. Results verified that marker-assisted selection is possible for the introgression of exotic FHB resistance genes, however, the genetic background of the recipient line and epistatic interactions can have a strong influence on expression and penetrance of any given gene.

Fusarium graminearum Chemotype-Spring Wheat Genotype Interaction Effects in Type I and II Resistance Response Assays

Fusarium head blight (FHB), caused by several Fusarium spp., is a worldwide problem that severely impacts cereal grain yield and poses major risks to human and animal health due to production of the mycotoxin deoxynivalenol (DON) and its acetylated forms, 3-acetyl-DON (3-ADON) and 15-acetyl-DON (15-ADON). Recent studies suggest an inconsistent effect of F. graminearum chemotypes and resistance of wheat (Triticum aestivum) genotypes. To gain insight into the interaction effects of F. graminearum chemotypes and spring wheat genotypes on FHB resistance response, 10 spring wheat genotypes with varying levels of FHB resistance were inoculated with 10 F. graminearum isolates, consisting of 5 3-ADON- and 5 15-ADON-producing isolates and evaluated in type I (spray inoculation) and type II (point inoculation) resistance assays. Wheat genotypes carrying the resistance allele of the Fhb1 quantitative trait locus on chromosome 3BS had lower disease in type II evaluations, regardless of F. graminearum isolate or chemotype. Isolates of F. graminearum were also significantly different for disease aggressiveness. In addition, the 3-ADON-producing isolates were 18% more aggressive than the 15-ADON isolates in type I resistance assays. No difference in aggressiveness of the two chemotypes was observed, when tested in type II resistance assays. There was no interaction effect between F. graminearum chemotypes and spring wheat genotypes, suggesting that screening of germplasm for resistance can be performed with limited number of aggressive isolates.

Validation of Molecular Markers for Use With Adapted Sources of Fusarium Head Blight Resistance in Wheat

Genetic control of resistance to Fusarium head blight (FHB) is quantitative, making phenotypic selection difficult. Genetic markers to resistance are helpful to select favorable genotypes. This study was conducted to determine if Fhb1 and Fhb5 present in the Sumai 3 source of FHB resistance occur in Sumai 3-derived North American spring wheat cultivars and to understand the appropriateness of using markers to select for the favorable alleles at these loci in breeding. Sumai 3-derived parents Alsen, ND3085, ND744, Carberry, and Glenn were used in crosses to generate 14 doubled haploid breeding populations. The parents and progeny were genotyped with five Fhb1 and three Fhb5 microsatellite markers. Progeny were selected based on performance relative to parents and other control cultivars in FHB nurseries near Portage la Prairie and Carman, MB. χ² and t test analyses were performed on marker and FHB data. The χ² test frequently determined the proportion of lines carrying molecular variants associated with FHB resistance increased following nursery selection for FHB. Similarly, the t test regularly demonstrated that selection for FHB resistance lowered the mean level of disease associated with resistant marker haplotypes. The study affirmed FHB resistance sources Alsen, Carberry, ND3085, and ND744 have Fhb1 and Fhb5 loci like Sumai 3, but no evidence was found that Glenn carries Fhb1 and Fhb5 resistance alleles. The results justified use of Fhb1 and Fhb5 markers for marker assisted selection in populations derived from Alsen, Carberry, ND3085, and ND744, but not Glenn. Combined or individual application of Xgwm493 and Xgwm533 in selection of genotypes carrying Fhb1, and Xgwm150, Xgwm304, and Xgwm595 for Fhb5 will enhance FHB resistance in wheat.

Mapping the A Genome for QTL Conditioning Resistance to Fusarium Head Blight in a Wheat Population with Triticum timopheevii Background

Development and use of resistant wheat cultivars is the most practical and economical approach for the control of Fusarium head blight (FHB). In the present study, a population of recombinant inbred lines derived from the cross between 'AC Brio' (a Canadian bread wheat cultivar moderately susceptible to FHB) and 'TC 67' (an FHB-resistant cultivar derived from Triticum timopheevii) was used to map quantitative trait loci (QTL) for FHB resistance using microsatellite molecular markers. Multiple interval mapping detected several QTL for FHB resistance on the chromosomes 5AL and 6A. The QTL detected in the marker interval of cfd6.1-barc48 on chromosome 5AL explained 10.9, 5.2, and 7.8% of phenotypic variation for disease incidence (type I resistance), disease severity (a combination of type I and type II resistance), and Fusarium-damaged kernels (FDK) (type IV resistance) under field conditions, respectively. The second QTL mapped to 5AL, in the marker interval of cfd39-cfa2185, explained 19.4 and 20.6% of phenotypic variation for FDK under field conditions and disease severity in the greenhouse (type II resistance), respectively. The QTL located on chromosome 6A conferred resistance to disease incidence and severity under field conditions and to disease severity in the greenhouse, explaining 6.8 to 11.8% of phenotypic variation for these traits. Several QTL for agronomic traits were also mapped in this study, including one and two QTL to the chromosomes 2A and 5AL, respectively, all for plant height, and two QTL to chromosome 6A for plant height and flowering date, respectively. The 5AL QTL for FHB resistance mapped in the marker interval of cfd39-cfa2185 in the present study is a novel QTL that originated from T. timopheevii and is reported here for the first time. Further validation of this QTL is required for wheat breeding programs to enhance resistance levels to FHB.

The Response of Selected Triticum spp. Genotypes with Different Ploidy Levels to Head Blight Caused by Fusarium culmorum (W.G.Smith) Sacc

Several cultivars and pure lines of Triticum monococcum, T. dicoccon, T. polonicum, T. spelta and T. aestivum were inoculated with Fusarium culmorum, the causal agent of Fusarium head blight in wheat. During the three-year study, the infection decreased the values of the analyzed yield components: spike weight (by 5.6% to 15.8%), number of kernels per spike (by 2.8% to 11.8%) and one kernel weight (by 8.4% to 10.7%). T. spelta was characterized by the weakest average response to infection. The grain from inoculated spikes contained significantly higher concentrations of deoxynivalenol (DON) and its 3-β-D-glucoside (D3G) than control grain. The D3G/DON ratio ranged from 11.4% to 21.4% in control grain and from 8.1% to 11.6% in inoculated grain. The lowest levels of mycotoxins were found in spelt, and the highest in T. polonicum lines and Kamut. PCA revealed that the grain of T. polonicum was characterized by an entirely different mycotoxin profile. The weakest response to F. culmorum infections was noted in T. spelta, and the strongest response in T. polonicum breeding lines and Kamut.

A proteomics survey on wheat susceptibility to Fusarium head blight during grain development

The mycotoxigenic fungal species Fusarium graminearum is able to attack several important cereal crops, such as wheat and barley. By causing Fusarium Head Blight (FHB) disease, F. graminearum induces yield and quality losses and poses a public health concern due to in planta mycotoxin production. The molecular and physiological plant responses to FHB, and the cellular biochemical pathways used by F. graminearum to complete its infectious process remain still unknown. In this study, a proteomics approach, combining 2D-gel approach and mass spectrometry, has been used to determine the specific protein patterns associated with the development of the fungal infection during grain growth on susceptible wheat. Our results reveal that F. graminearum infection does not deeply alter the grain proteome and does not significantly disturb the first steps of grain ontogeny but impacts molecular changes during the grain filling stage (impact on starch synthesis and storage proteins). The differentially regulated proteins identified were mainly involved in stress and defence mechanisms, primary metabolism, and main cellular processes such as signalling and transport. Our survey suggests that F. graminearum could take advantage of putative susceptibility factors closely related to grain development processes and thus provide new insights into key molecular events controlling the susceptible response to FHB in wheat grains.

Variations for Fusarium head blight resistance associated with genomic diversity in different sources of the resistant wheat cultivar 'Sumai 3'

Fusarium head blight (FHB), caused by Fusarium graminearum, is a serious disease of wheat (Triticum aestivum L.) associated with contamination by the mycotoxin deoxynivalenol (DON). The FHB-resistant wheat cultivar 'Sumai 3' has been used extensively around the world. The existence of variation in FHB resistance among 'Sumai 3' accessions has been discussed. In this study, genetic variation among 'Sumai 3' accessions collected from six countries were identified using SSR markers; our results demonstrate unique chromosome regions in Sumai 3-AUT and Sumai 3-JPN ('Sumai 3' accessions from Austria and Japan, respectively). Field evaluation indicated strong resistance to FHB in Sumai 3-AUT. The polymorphic rate (number of polymorphic markers/number of available markers × 100) based on a DArT array was 12.5% between the two 'Sumai 3' accessions. Genotyping for DNA markers flanking FHB-resistant quantitative trait loci (QTLs) revealed genetic variations for the QTL regions on 5AS and 2DS; however, no variation was observed for the QTL regions on 3BS and 6B. Thus, the variation in FHB resistance among 'Sumai 3' accessions in the field is due to genetic diversity.

Identification of functional genic components of major fusarium head blight resistance quantitative trait loci in wheat cultivar Sumai 3

Fusarium head blight (FHB) is a devastating disease worldwide, affecting wheat and other small grains. To identify key wheat genes involved in FHB pathogenesis, 406 FHB-related wheat expressed sequence tags functionally identified in Sumai 3 were investigated for their association with FHB-resistance quantitative trait loci (QTL) Fhb1 and Fhb_6BL in 2010 and 2011. A total of 47 candidate genes were identified by bulk analysis, near-isogenic screening and expression QTL mapping, and were finally mapped to their carrier chromosomes with Chinese Spring nulli-tetra deficiency lines. One gene, designated WFhb1_c1 (wheat Fhb1 candidate gene 1), was both functionally associated with and physically located within Fhb1 and was found to be weakly similar (E = 5e+0) to an Arabidopsis gene encoding pectin methyl esterase inhibitor. Two other genes, designated WFI_6BL1 and WFI_6BL2 (wheat-Fusarium interaction genes 6BL1 and 6BL2), were functionally associated with Fhb_6BL but physically mapped on chromosomes 7D and 5A, respectively. WFI_6BL1 was annotated as a 13- lipoxygenase gene and WFI_6BL2 might encode a PR-4-like protein. Our data suggested that i) Fhb1 seems to contribute to FHB resistance by reducing susceptibility in the first 60 h, ii) Fhb_6BL makes its contribution via the jasmonate-mediated pathways, and iii) wheat seems to activate its defense mechanism in the biotrophic phase of FHB pathogenesis.

Efficacy and Stability of Integrating Fungicide and Cultivar Resistance to Manage Fusarium Head Blight and Deoxynivalenol in Wheat

Integration of host resistance and prothioconazole + tebuconazole fungicide application at anthesis to manage Fusarium head blight (FHB) and deoxynivalenol (DON) in wheat was evaluated using data from over 40 trials in 12 U.S. states. Means of FHB index (index) and DON from up to six resistance class-fungicide management combinations per trial (susceptible treated [S_TR] and untreated [S_UT]; moderately susceptible treated [MS_TR] and untreated [MS_UT]; moderately resistant treated [MR_TR] and untreated [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( ) due to the management combinations relative to S_UT. All combinations led to a significant reduction in index and DON (P < 0.001). MR_TR was the most effective combination, with a of 76% for index and 71% for DON, followed by MS_TR (71 and 58%, respectively), MR_UT (54 and 51%, respectively), S_TR (53 and 39%, respectively), and MS_UT (43 and 30%, respectively). Calculations based on the principle of treatment independence showed that the combination of fungicide application and resistance was additive in terms of percent control for index and DON. Management combinations were ranked based on percent control relative to S_UT within each trial, and nonparametric analyses were performed to determine management combination stability across environments (trials) using the Kendall coefficient of concordance (W). There was a significant concordance of management combinations for both index and DON (P < 0.001), indicating a nonrandom ranking across environments and relatively low variability in the within-environment ranking of management combinations. MR_TR had the highest mean rank (best control relative to S_UT) and was one of the most stable management combinations across environments, with low rank stability variance (0.99 for index and 0.67 for DON). MS_UT had the lowest mean rank (poorest control) but was also one of the most stable management combinations. Based on Piepho's nonparametric rank-based variance homogeneity U test, there was an interaction of management combination and environment for index (P = 0.011) but not for DON (P = 0.147), indicating that the rank ordering for index depended somewhat on environment. In conclusion, although the magnitude of percent control will likely vary among environments, integrating a single tebuconazole + prothioconazole application at anthesis with cultivar resistance will be a more effective and stable management practice for both index and DON than either approach used alone.

Marker-assisted selection for disease resistance in wheat and barley breeding

Marker-assisted selection (MAS) provides opportunities for enhancing the response from selection because molecular markers can be applied at the seedling stage, with high precision and reductions in cost. About each of 50 genes conferring monogenic resistances and hundreds of quantitative trait loci (QTL) for quantitative disease resistances have been reported in wheat and barley. For detecting single-major gene resistance, MAS could be easily applied, but is often not necessary because the resistances are selected phenotypically. In quantitative disease resistances, MAS would be very useful, but the individual QTL often have small effects. Additionally, only a few monogenic resistances are durable and only a few QTL with high effects have been successfully transferred into elite breeding material. Further economic and biological constraints, e.g., a low return of investment in small-grain cereal breeding, lack of diagnostic markers, and the prevalence of QTL-background effects, hinder the broad implementation of MAS. Examples in which MAS has been successfully applied to practical breeding are the wheat rust resistance genes Lr34 and Yr36, the eyespot resistance gene Pch1, the recessive resistance genes rym4/rym5 to barley yellow mosaic viruses, mlo to barley powdery mildew, and two QTL for resistance to Fusarium head blight in wheat (Fhb1 and Qfhs.ifa-5A). Newly identified broad-spectrum resistance genes/QTL conferring resistance to multiple taxa of pathogens offer additional perspectives for MAS. In the future, chip-based, high-throughput genotyping platforms and the introduction of genomic selection will reduce the current problems of integrating MAS in practical breeding programs and open new avenues for a molecular-based resistance breeding.

Fusarium graminearum forms mycotoxin producing infection structures on wheat

BACKGROUND

The mycotoxin producing fungal pathogen Fusarium graminearum is the causal agent of Fusarium head blight (FHB) of small grain cereals in fields worldwide. Although F. graminearum is highly investigated by means of molecular genetics, detailed studies about hyphal development during initial infection stages are rare. In addition, the role of mycotoxins during initial infection stages of FHB is still unknown. Therefore, we investigated the infection strategy of the fungus on different floral organs of wheat (Triticum aestivum L.) under real time conditions by constitutive expression of the dsRed reporter gene in a TRI5prom::GFP mutant. Additionally, trichothecene induction during infection was visualised with a green fluorescent protein (GFP) coupled TRI5 promoter. A tissue specific infection pattern and TRI5 induction were tested by using different floral organs of wheat. Through combination of bioimaging and electron microscopy infection structures were identified and characterised. In addition, the role of trichothecene production for initial infection was elucidated by a ΔTRI5-GFP reporter strain.

RESULTS

The present investigation demonstrates the formation of foot structures and compound appressoria by F. graminearum. All infection structures developed from epiphytic runner hyphae. Compound appressoria including lobate appressoria and infection cushions were observed on inoculated caryopses, paleas, lemmas, and glumes of susceptible and resistant wheat cultivars. A specific trichothecene induction in infection structures was demonstrated by different imaging techniques. Interestingly, a ΔTRI5-GFP mutant formed the same infection structures and exhibited a similar symptom development compared to the wild type and the TRI5prom::GFP mutant.

CONCLUSIONS

The different specialised infection structures of F. graminearum on wheat florets, as described in this study, indicate that the penetration strategy of this fungus is far more complex than postulated to date. We show that trichothecene biosynthesis is specifically induced in infection structures, but is neither necessary for their development nor for formation of primary symptoms on wheat.

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

A Chinese Spring-Sumai 3 chromosome 7A disomic substitution line (CS-Sumai 3-7ADSL) was reported to have a high level of Fusarium head blight (FHB) resistance for symptom spread within a spike (Type II) and low deoxynivalenol accumulation in infected kernels (Type III), but a quantitative trait locus (QTL) on chromosome 7A has never been identified from this source. To characterize QTL on chromosome 7A, we developed 191 7A chromosome recombinant inbred lines (7ACRIL) from a cross between Chinese Spring and CS-Sumai 3-7ADSL and evaluated both types of resistance in three greenhouse experiments. Two major QTL with Sumai 3 origin, conditioning both Type II and III resistance, were mapped in the short arm of chromosomes 3B (3BS) and near the centromere of chromosome 7A (7AC). The 3BS QTL corresponds to previously reported Fhb1 from Sumai 3, whereas 7AC QTL, designated as Fhb7AC, is a novel QTL identified from CS-Sumai 3-7ADSL in this study. Fhb7AC explains 22% phenotypic variation for Type II and 24% for Type III resistance. Marker Xwmc17 is the closest marker to Fhb7AC for both types of resistance. Fhb1 and Fhb7AC were additive, and together explained 56% variation for Type II and 41% for Type III resistance and resulted in 66% reduction in FHB severity and 84% reduction in deoxynivalenol (DON) content. Haplotype analysis of Sumai 3 parents revealed that Fhb7AC originated from Funo, an Italian cultivar. Fhb7AC has the potential to be used in improving wheat cultivars for both types of resistance.

Saturation and mapping of a major Fusarium head blight resistance QTL on chromosome 3BS of Sumai 3 wheat

Fusarium head blight (FHB) is a destructive disease in wheat. The major quantitative trait locus (QTL) on 3BS from Sumai 3 and its derivatives has been used as a major source of the resistance to FHB worldwide, but the discrepancy in reported location of the major QTL could block its using in map based cloning and marker assisted selection. In this study, Chinese Spring-Sumai 3 chromosome 3B substitution line was used as resistant parent of the mapping population to reduce the confounded effect of genetic background in Sumai 3. The major QTL region was saturated with the Sequence Tagged Microsatellite (STM) and Sequence Tagged Site (STS) markers. A linkage map of chromosome 3B with 36 markers covering a genetic distance of 112.4 cM was constructed. Twelve new markers were inserted into the chromosome region where the major QTL was located. The average interval distance between markers was 1.5 cM. Multiple QTL Models (MQM) mapping indicated that the major QTL was located in the interval of Xgwm533-Xsts9-1, and explained 45.6% of phenotypic variation of the resistance to FHB. The SSR (simple sequence repeat) marker Xgwm533 and STM marker Xstm748tcac are closely linked to the major QTL.

Estimating mycotoxin contents of Fusarium-damaged winter wheat kernels

Winter wheat (Triticum aestivum L., cultivars Ritmo and Dekan) grain was sampled in Northern Germany between 2001 and 2006. Kernels damaged by fungi of the genus Fusarium were separated from sound grain by visual assessment. Samples containing 0%, 20%, 40%, 60%, 80% and 100% of Fusarium-damaged kernels were compiled and analyzed for the Fusarium type B trichothecenes deoxynivalenol (DON, 2001-2006), nivalenol (NIV, 2006), 3-acetyl-deoxynivalenol (3AcDON, 2006) and 15-acetyl-deoxynivalenol (15AcDON, 2006). The relationship between mycotoxin contents and the percentage of Fusarium-damaged kernels was calculated for each lot of grain. Apart from one exception, relationships between the percentage of Fusarium-damaged kernels and NIV, 3AcDON or 15AcDON were non-significant. In contrast, close relationships between the percentage of Fusarium-damaged kernels and the DON content were observed (r(2)=0.93-0.99). The y-axis intercepts were not significantly different from zero, but the DON content of the damaged kernels varied by a factor of 11.59 between years and by a factor of 1.87 between cultivars. Fusarium-damaged kernels contained between 0.21 and 2.39 microg DON kernel(-1). The overall average DON content of a Fusarium-damaged wheat kernel was 1.29 +/- 0.11 microg. The DON content of diseased kernels was affected by environment and wheat genotype but not by genotype x environment interaction. On average, Fusarium-damaged kernels contained 9.7-fold more DON than 15AcDON, 19.5-fold more DON than NIV, and 26.9-fold more DON than 3AcDON. 3AcDON and 15AcDON contents per wheat kernel were not significantly different between cultivars. On average, 4.27% of Fusarium-damaged kernels were sufficient to reach the 1.25 mg DON kg(-1) grain limit for unprocessed cereals in the EU. Given the low percentages of Fusarium-damaged kernels that are equivalent to current legal DON limits, grading accuracies >96% would be needed when using automatic grading systems for separating sound from damaged kernels.

QTL analysis of resistance to Fusarium head blight in the novel wheat germplasm CJ 9306. II. Resistance to deoxynivalenol accumulation and grain yield loss

Fusarium head blight (FHB or scab) caused by Fusarium species is a destructive disease in wheat, not only causing dramatic decrease of grain yield and quality, but also leading to serious mycotoxin contamination in the infected grains. This study was conducted to identify and quantify quantitative trait loci (QTLs) contributing to resistance to deoxynivalenol (DON) accumulation as well as to grain yield loss in a population of 152 F(7) recombinant inbred lines (RILs) derived from the cross Veery/CJ 9306. DON content in scabby grains and relative decreases of yield components were analyzed. Two new QTLs (QFhs.nau-2DL and QFhs.nau-1AS) for resistance to DON accumulation caused by FHB in wheat were detected, and QTLs QFhs.ndsu-3BS and QFhs.nau-5AS were also validated in CJ 9306, based on a constructed genetic linkage map. On the average of three experiments, major QTLs QFhs.ndsu-3BS and QFhs.nau-2DL explained up to 23 and 20% of phenotypic variation, respectively. QFhs.nau-1AS and QFhs.nau-5AS separately explained 4-6% of phenotypic variation. The differences among years/experiments were significant for all the four QTLs. However, the QTL x environment interaction was significant only for QFhs.nau-2DL, but not for the others. The results suggest that simple sequence repeat (SSR) markers Xgwm533b associated with QFhs.ndsu-3BS, and Xgwm539 associated with QFhs.nau-2DL could be used in marker-assisted selection to enhance resistance to DON accumulation. QFhs.ndsu-3BS + QFhs.nau-2DL and QFhs.nau-2DL + QFhs.nau-5AS would be the optimum choices for two-locus combinations. QFhs.ndsu-3BS was also validated in CJ 9306 for resistance to grain yield loss, explaining 8-15% of phenotypic variation. No QTLs for resistance to DON accumulation or grain yield loss independent of Type II resistance were found. By comparison, however, either of QFhs.nau-2DL or QFhs.nau-5AS alone and their combination were more contributive to resistance to DON accumulation than to Type II resistance.

Molecular mapping of kernel shattering and its association with Fusarium head blight resistance in a Sumai3 derived population

Kernel shattering (KS) can cause severe grain yield loss in wheat (Triticum aestivum L.). The introduction of genotypes with Fusarium head blight (FHB) resistance has elevated the KS importance. 'Sumai3,' the most commonly used FHB-resistant germplasm worldwide, is reported to be KS susceptible. The objectives of this study were to detect quantitative trait loci (QTLs) for KS and to determine the relationship between KS and FHB. A recombinant inbred line population derived from a cross between Sumai3 and 'Stoa' was evaluated for KS in five environments and FHB in two field trials, separately. Four genomic regions on chromosomes 2B, 3B, and 7A were associated with KS. Of them, two major KS QTLs were detected consistently over three environments and each located proximal to the centromere on chromosomes 3B and 7A. The resistant alleles at these two QTLs together can reduce KS by 66.1% relative to the reciprocal alleles and by 41.1% compared to the population mean. The field FHB data revealed four QTLs on chromosomes 2B, 3B, and 7A. Three of these FHB QTLs coincided with and/or linked to the KS QTLs with opposite allele effects in the corresponding genomic regions, which may explain the negative correlation (r = -0.29 and P < 0.01) between the KS and FHB infection found in this study. The results in this study indicate that KS and FHB in Sumai3 are, in part, inherited dependently. However, the correlation between KS and FHB is not strong, and the major FHB resistance QTL on chromosome arm 3BS was not linked to any KS QTL. Our results showed that pyramiding of the two major KS-resistant alleles and the unlinked major FHB-resistant allele could produce lines with both low values of KS and FHB infection.

Identification of a Novel Fusarium Head Blight Resistance Quantitative Trait Locus on Chromosome 7A in Tetraploid Wheat

ABSTRACT Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most destructive diseases of durum (Triticum turgidum sp. durum) and common wheat (T. aestivum). Promising sources of FHB resistance have been identified among common (hexaploid) wheats, but the same is not true for durum (tetraploid) wheats. A previous study indicated that chromosome 7A from T. turgidum sp. dicoccoides accession PI478742 contributed significant levels of resistance to FHB. The objectives of this research were to develop a genetic linkage map of chromosome 7A in a population of 118 recombinant inbred lines derived from a cross between the durum cv. Langdon (LDN) and a disomic LDN-T. turgidum sp. dicoccoides PI478742 chromosome 7A substitution line [LDN-DIC 7A(742)], and identify a putative FHB resistance quantitative trait locus (QTL) on chromosome 7A derived from LDN-DIC 7A(742). The population was evaluated for type II FHB resistance in three greenhouse environments. Interval regression analysis indicated that a single QTL designated Qfhs.fcu-7AL explained 19% of the phenotypic variation and spanned an interval of 39.6 cM. Comparisons between the genetic map and a previously constructed physical map of chromosome 7A indicated that Qfhs.fcu-7AL is located in the proximal region of the long arm. This is only the second FHB QTL to be identified in a tetraploid source, and it may be useful to combine it with the QTL Qfhs.ndsu-3AS in order to develop durum wheat germ plasm and cultivars with higher levels of FHB resistance.

Deletion of a Chromosome Arm Altered Wheat Resistance to Fusarium Head Blight and Deoxynivalenol Accumulation in Chinese Spring

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, is an important disease of wheat worldwide. Production of deoxynivalenol (DON) in infected wheat grain by F. graminearum is a major safety concern when considering use of the grain as feed for livestock or for human consumption. Determining chromosome locations of FHB-related genes may facilitate enhancement of wheat resistance to FHB and DON accumulation. In this study, a set of 30 ditelosomic lines derived from Chinese Spring, a moderately FHB-resistant landrace from China, were evaluated for proportion of scabbed spikelets per inoculated spike in the greenhouse and for DON contamination in harvested grain over 2 years. Significant variation in the proportion of scabbed spikelets was observed among ditelosomic lines, ranging from 13 to 95%. Seven ditelosomic lines exhibited a greater proportion of scabbed spikelets and three of these also had greater DON content than Chinese Spring (P = 0.01), suggesting that those missing chromosome arms may carry genes that contribute to resistance to FHB. Six ditelosomic lines had a reduction in proportion of scabbed spikelets, suggesting that susceptibility factors or resistance suppressors may be on these missing chromosomal arms. Selection for low proportion of scabbed spikelets in general will select for low DON content.

Main effects, epistasis, and environmental interactions of quantitative trait Loci for fusarium head blight resistance in a recombinant inbred population

ABSTRACT Chinese Spring Sumai 3 chromosome 7A disomic substitution line (CS-SM3-7ADS) is highly resistant to Fusarium head blight (FHB), and an F(7) population of recombinant inbred lines derived from the cross CS-SM3-7ADS x Annong 8455 was evaluated for resistance to FHB to investigate main effects, epistasis, and environmental interactions of quantitative trait loci (QTLs) for FHB resistance. A molecular linkage map consists of 501 simple sequence repeat and amplified fragment length polymorphism markers. A total of 10 QTLs were identified with significant main effects on the FHB resistance using MapQTL and QTLMapper software. Among them, CS-SM3-7ADS carries FHB-resistance alleles at five QTLs on chromosomes 2D, 3B, 4D, and 6A. One QTL on 3BS had the largest effect and explained 30.2% of the phenotypic variance. Susceptible QTLs were detected on chromosomes 1A, 1D, 4A, and 4B. A QTL for enhanced FHB resistance was not detected on chromosome 7A of CS-SM3-7ADS; therefore, the increased FHB resistance in CS-SM3-7ADS was not due to any major FHB-resistance QTL on 7A of Sumai 3, but more likely was due to removal of susceptible alleles of QTLs on 7A of Chinese Spring. QTLMapper detected nine pairs of additive-additive interactions at 17 loci that explained 26% phenotypic variance. QTL-environment interactions explained 49% of phenotypic variation, indicating that the environments significantly affected the expression of the QTLs, especially these epistasis QTLs. Adding FHB-enhancing QTLs or removal of susceptible QTLs both may significantly enhance the degree of wheat resistance to FHB in a wheat cultivar.

Relationship between visual estimates of fusarium head blight intensity and deoxynivalenol accumulation in harvested wheat grain: a meta-analysis

ABSTRACT The association between Fusarium head blight (FHB) intensity and deoxynivalenol (DON) accumulation in harvested grain is not fully understood. A quantitative review of research findings was performed to determine if there was a consistent and significant relationship between measures of Fusarium head blight intensity and DON in harvested wheat grain. Results from published and unpublished studies reporting correlations between DON and Fusarium head blight "index" (IND; field or plot-level disease severity), incidence (INC), diseased-head severity (DHS), and Fusarium-damaged kernels (FDK) were analyzed using meta-analysis to determine the overall magnitude, significance, and precision of these associations. A total of 163 studies was analyzed, with estimated correlation coefficients (r) between -0.58 and 0.99. More than 65% of all r values were >0.50, whereas less that 7% were <0. The overall mean correlation coefficients for all relationships between DON and disease intensity were significantly different from zero (P < 0.001). Based on the analysis of Fisher-transformed r values ( z(r) values), FDK had the strongest relationship with DON, with a mean r of 0.73, followed by IND (r = 0.62), DHS (r = 0.53), and INC (r = 0.52). The mean difference between pairs of transformed z(r) values (z(d) ) was significantly different from zero for all pairwise comparisons, except the comparison between INC and DHS. Transformed correlations were significantly affected by wheat type (spring versus winter wheat), study type (fungicide versus genotype trials), and study location (U.S. spring- and winter-wheat-growing regions, and other wheat-growing regions). The strongest correlations were observed in studies with spring wheat cultivars, in fungicide trials, and in studies conducted in U.S. spring-wheat-growing regions. There were minor effects of magnitude of disease intensity (and indirectly, environment) on the transformed correlations.

Molecular characterization of Fusarium head blight resistance in Wangshuibai with simple sequence repeat and amplified fragment length polymorphism markers

Molecular mapping of Fusarium head blight (FHB) resistance quantitative trait loci (QTL) and marker-assisted selection of these QTL will aid in the development of resistant cultivars. Most reported FHB resistance QTL are from 'Sumai 3' and its derivatives. 'Wangshuibai' is a FHB-resistant landrace that originated from China and is not known to be related to 'Sumai 3'. A mapping population of 139 F(5:6) recombinant inbred lines was developed from a cross of 'Wangshuibai' and 'Wheaton'. This population was developed to map the FHB-resistant QTL in 'Wangshuibai' and was evaluated twice for Type II FHB resistance. A total of 1196 simple sequence repeat and amplified fragment length polymorphism markers were screened on this population, and four FHB resistance QTL were detected. A major QTL near the end of 3BS explained 37.3% of the phenotypic variation. Another QTL on 3BS, located close to the centromere, explained 7.4% of the phenotypic variation. Two additional QTL on 7AL and 1BL explained 9.8% and 11.9% of the phenotypic variation, respectively. The simple sequence repeat and amplified fragment length polymorphism markers closely linked to these QTL may be useful for stacking QTL from 'Wangshuibai' and other sources to develop cultivars with transgressive FHB resistance.

Development and mapping of microsatellite (SSR) markers in wheat

Microsatellite DNA markers are consistently found to be more informative than other classes of markers in hexaploid wheat. The objectives of this research were to develop new primers flanking wheat microsatellites and to position the associated loci on the wheat genome map by genetic linkage mapping in the ITMI W7984 x Opata85 recombinant inbred line (RIL) population and/or by physical mapping with cytogenetic stocks. We observed that the efficiency of marker development could be increased in wheat by creating libraries from sheared rather than enzyme-digested DNA fragments for microsatellite screening, by focusing on microsatellites with the [ATT/TAA]n motif, and by adding an untemplated G-C clamp to the 5'-end of primers. A total of 540 microsatellite-flanking primer pairs were developed, tested, and annotated from random genomic libraries. Primer pairs and associated loci were assigned identifiers prefixed with BARC (the acronym for the USDA-ARS Beltsville Agricultural Research Center) or Xbarc, respectively. A subset of 315 primer sets was used to map 347 loci. One hundred and twenty-five loci were localized by physical mapping alone. Of the 222 loci mapped with the ITMI population, 126 were also physically mapped. Considering all mapped loci, 126, 125, and 96 mapped to the A, B, and D genomes, respectively. Twenty-three of the new loci were positioned in gaps larger than 10 cM in the map based on pre-existing markers, and 14 mapped to the ends of chromosomes. The length of the linkage map was extended by 80.7 cM. Map positions were consistent for 111 of the 126 loci positioned by both genetic and physical mapping. The majority of the 15 discrepancies between genetic and physical mapping involved chromosome group 5.

Host genetic effect on deoxynivalenol accumulation in fusarium head blight of barley

ABSTRACT One of the major concerns with Fusarium head blight (FHB) of barley is the potential health risks to livestock and humans through the accumulation of the mycotoxin deoxynivalenol (DON) in infected grain. To define the role of the host in DON accumulation during the early stages of disease development, we conducted a series of greenhouse experiments. We inoculated single spikelets of greenhouse-grown plants with Fusarium graminearum, moved the plants to a dew chamber, and harvested the inoculated spikelets after 72 h for DON analysis. We conducted a quantitative trait locus (QTL) analysis using a genetic mapping population, constructed with the parents Stander and Frederickson, that segregated for DON accumulation after single-spikelet inoculation in two experiments. A single QTL on chromosome 3 explained 18 and 35% of the phenotypic variation in the two experiments. To validate this QTL for DON accumulation, we used a DNA marker to select near-isogenic lines from a family from the mapping population that was segregating at this QTL. Disease symptom development was similar between the nearisogenic lines; however, the mean DON concentration of the lines homozygous for the allele from the high DON parent was 2.5-fold more than the lines homozygous for the alternate allele. A time course experiment showed that this effect on toxin accumulation was observed at 10 days post inoculation. The near-isogenic lines developed in this study should prove useful for further exploration of the role of DON in FHB.