Mapping of quantitative trait Loci for fusarium head blight resistance in barley

ABSTRACT Fusarium head blight (FHB) is a devastating disease that causes significant reductions in yield and quality in wheat and barley. Barley grains infected with deoxynivalenol (DON), a vomitoxin produced by Fusarium graminearum, are rejected for malting and brewing. Among six-rowed barley cultivars tested thus far, only cv. Chevron exhibited resistance. This study was conducted to map genes and to identify DNA markers for marker-assisted breeding for FHB resistance in cv. Chevron with restriction fragment length polymorphism (RFLP) markers. A doubled haploid (DH) population was created from a cross between cv. Chevron and susceptible cv. Stander. Seven field experiments were conducted in four different locations in 2 years. A RFLP map containing 211 loci and covering over 1,000 centimorgans (cM) of the genome was used to map quantitative trait loci (QTL) associated with relatively low FHB severity and DON concentration. Morphological traits differing between the parents were also measured: heading date, plant height, spike angle, number of nodes per cm of rachis in the spike, and kernel plumpness. Many of the QTL for FHB and DON coincided with QTLs for these morphological traits. The "fix-QTL" algorithm in Mapmaker QTL was used to remove the part of the variance for FHB resistance that may be explained by heading date or plant height. Results from this study suggest that QTLs with major effects for FHB resistance probably do not exist in cv. Chevron. Three QTL intervals, Xcmwg706-Xbcd441 on chromosome 1H, Xbcd307b-Xcdo684b on chromosome 2H, and Xcdo959b-Xabg472 on chromosome 4H, that are not associated with late heading or height may be useful for marker-assisted selection.     

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.     

大麦赤霉病鉴定方法与抗性评价

为探讨以病小穗率与病穗率作为抗性评价指标的精确度,利用单花滴注、孢子液喷雾分别结合土表病麦粒接种的方法,评价了2个大麦重组自交系群体131个株系对赤霉病的抗侵染与抗扩展性。单花滴注接种后调查了第7、14和21天的病情性状,接种后第7天所有株系均感病,病小穗率最低的为1.59%,第21天最高病小穗率为58.91%;孢子液喷雾接种后第21天材料全部感病,其中6棱株系的感病程度高于2棱株系。以病小穗率和病穗率划分赤霉病抗性的分布情况,发现病小穗率更能有效区分株系的赤霉病抗性。相关分析显示,病小穗率、病穗率、禾谷镰刀菌烯醇含量与粒色和穗密度呈显著负相关,而与株高、抽穗期无显著相关。     

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

ABSTRACT Fusarium head blight (FHB) or scab is a destructive disease of barley in many countries. A better understanding of the interrelationships between plant traits and FHB resistance should help in the development of effective and efficient breeding strategies for FHB-resistant cultivars. Recent mapping studies indicate that many of the quantitative trait loci (QTL) for FHB resistance coincide with the QTL for plant height, heading date, and spike characteristics. Therefore, a study was conducted to investigate the relationship of morphological and physiological traits to FHB infection and deoxynivalenol (DON) accumulation in a barley doubled-haploid (DH) population derived from a Léger x CI9831 cross. Approximately 190 DH lines were grown at Ottawa (Ontario) for 2 years, Charlottetown (Prince Edward Island) for 1 year, and Hangzhou (Zhejiang) for 2 years. The field plots were inoculated with Fusarium graminearum at each location. FHB incidence was positively correlated with DON content. Resistance to FHB was associated with two-row spike, purple lemma, long glume awn, tall stature, and resistance to lodging, but it was not associated with long rachilla hairs, rough lemma awn, or heading date. Two-row spike was associated with tall stature and resistance to lodging. These associations as well as its spike characteristics helped reduce FHB infection and DON accumulation in two-row lines compared with six-row lines. The association between long glume awn and FHB resistance could be due to genetic linkages. Therefore, trait associations should be taken into consideration when breeding for FHB resistance and interpreting data from FHB experiments.     

Effect of infection timing on fusarium head blight and mycotoxin accumulation in open- and closed-flowering barley

ABSTRACT Barley has two flowering types, chasmogamous (open-flowering) and cleistogamous (closed-flowering). We examined the effect of the timing of Fusarium graminearum infection on Fusarium head blight (FHB) and mycotoxin accumulation in barley cultivars with different flowering types using greenhouse experiments. In the first experiment, 13 cultivars were spray inoculated at two different developmental stages, and the severity of FHB was evaluated. The effect of the timing of infection differed among cultivars. Cleistogamous cultivars were resistant at anthesis but susceptible at 10 days after anthesis, whereas chasmogamous cultivars were already susceptible at anthesis. In the second experiment, five cultivars were inoculated at three different developmental stages and the concentrations of deoxynivalenol (DON) and nivalenol (NIV) in mature grain were analyzed. Cleistogamous cultivars accumulated more mycotoxins (DON and NIV) when inoculated 10 or 20 days after anthesis than when inoculated at anthesis, whereas chasmogamous cultivars accumulated more mycotoxins when inoculated at anthesis. Thus, the most critical time for F. graminearum infection and mycotoxin accumulation in barley differs with cultivar, and likely is associated with the flowering type. Late infection, even without accompanied FHB symptoms, was also significant in terms of the risk of mycotoxin contamination.     

Evaluation of type I fusarium head blight resistance of wheat using non-deoxynivalenol-producing fungi

A series of experiments was conducted to determine whether type I resistance (resistance to initial infection) to fusarium head blight (FHB) in wheat could be assessed using fungal species/isolates that do not produce deoxynivalenol (DON), a mycotoxin critical to the spread of Fusarium graminearum in the wheat spike. It was shown that, while the non-toxin-producing species Microdochium nivale and M. majus could infect following spray inoculation of wheat spikes, they were unable to spread within the spike following point inoculation. However, although these species might reveal type I resistance, they are not highly pathogenic towards wheat. A nivalenol (NIV)-producing isolate of F. graminearum caused high levels of disease following spray inoculation, but spread only very slowly within the spike and rarely induced bleaching above the point of inoculation. It is proposed that spray inoculation with an appropriate, aggressive, non-DON-producing FHB pathogen may be used to characterize type I resistance to complement point inoculation with a DON-producing isolate to assess type II resistance (resistance to spread within the spike).     

Comparison of spray and point inoculation to assess resistance to fusarium head blight in a multienvironment wheat trial

ABSTRACT Fusarium head blight (FHB, scab), caused by Fusarium graminearum or F. culmorum, results in yield and quality reductions and accumulation of mycotoxins. Two inoculation methods are commonly used. Spraying a spore suspension on the head (spray inoculation) will detect resistance to initial infection (type I) and to disease spread within the spike (type II). Injecting a spore suspension into individual florets (point inoculation) will detect type II resistance only. To analyze the association of spray and point inoculation, 20 elite winter wheat cultivars from Romania, Germany, and Switzerland were inoculated in factorial field experiments in seven environments (location x year combinations) in Germany and Romania. Response to FHB was assessed by the percentage of visually infected spikelets and head weight relative to the noninoculated control. Point and spray inoculations resulted in a mean disease severity varying from 52 to 63%. Significant (P = 0.01) genotypic variation was found within and across the environments. Genotype-environment interaction was important also. Estimates of entry-mean heritability were higher for spray than for point inoculation as assessed by percent infected spikelets (0.81 versus 0.77) and relative head weight (0.77 versus 0.52). Significant (P = 0.01) interaction was found between inoculation methods. Consequently, coefficients of phenotypic correlation between both methods were low to medium for percent infected spikelets (0.40, P > 0.1) and relative head weight (0.52, P = 0.05). We conclude that the application of both inoculation methods should provide additional information for selection and scientific studies. Spray inoculation, however, is less laborious for large-scale routine screening of breeding materials.     

Effects of plant height on type I and type II resistance to fusarium head blight in wheat

By carefully separating type I and type II resistances, the possible effects of plant height on fusarium head blight (FHB) resistance in wheat were assessed using near‐isogenic lines (NILs) for several different reduced‐height (Rht) genes. Tall isolines all gave better type I resistance than their respective dwarf counterparts when assessed at their natural heights. These differences largely disappeared when the dwarf isolines were physically raised so that their spikes were positioned at the same height as those of their respective tall counterparts. The effects of plant height on type II resistance was less clear. For those NIL pairs which showed significant differences, it was the dwarf isolines which gave better resistance. As the Rht genes involved in these NILs locate at different genomic regions, the differences in FHB between the dwarf and tall isolines are unlikely to be the result of linkages between each of the different Rht loci with a beneficial or a deleterious gene affecting type I or type II resistance. Rather, the different FHB resistances are probably caused by direct or indirect effects of height difference per se, and microclimate may have contributed to the better type I resistance of the tall plants. Thus, caution should be exercised when attempting to exploit any of the FHB resistant loci co‐located with Rht genes.     

Inverse effects of Arabidopsis NPR1 gene on fusarium seedling blight and fusarium head blight in transgenic wheat

In this study, the Arabidopsis thaliana NPR1 (non‐expressor of PR genes) gene was integrated into an elite wheat cultivar, and the response of the transgenic wheat expressing NPR1 to inoculation with Fusarium asiaticum was analysed. With seedling inoculation, the transgenic lines showed significantly increased fusarium seedling blight (FSB) susceptibility, whereas floret inoculation resulted in enhanced fusarium head blight (FHB) resistance. Quantitative real‐time PCR revealed that expression of two defence genes, PR3 and PR5, was associated with susceptible reactions to FSB and FHB, whereas the PR1 gene was activated in resistance responses. This inverse modulation by the constitutively expressed NPR1 gene suggests that NPR1 has a bifunctional role in regulating defence responses in plants. Therefore, it is unsuitable for improving overall resistance to FSB and FHB in wheat.     

Evaluation and characterization of resistance to fusarium head blight caused by Fusarium culmorum in UK winter wheat cultivars

Fusarium head blight (FHB) resistance of 50 cultivars from the National List of winter wheat cultivars approved for sale (or were undergoing trails for approval in 2003) in the UK was compared with 21 reference cultivars from continental Europe which had previously been characterized for resistance. Only three UK National List cultivars (Soissons, Spark and Vector) had stable resistance over trial sites that was significantly greater than that of the FHB susceptible cultivar Wizard. In addition, under moderate disease pressure, 21 of the National List cultivars had levels of the trichothecene mycotoxin deoxynivalenol (DON) above the proposed European Union limit of 1·25 ppm in grain. Surveys show that levels of FHB and DON in the UK crop are currently very low, however, should disease pressure increase for any reason, then an improvement in the overall levels of FHB resistance of UK winter wheat germplasm will be required. In order to infer the origin of resistance and to identify potentially novel resistance, allele sizes of microsatellite (simple sequence repeat, SSR) markers linked to quantitative trait loci (QTL) for FHB resistance were compared between the test cultivars and known, characterized resistance sources. The major FHB resistance QTL from the Chinese cv. Sumai-3 (3BS, 5A and 6B), the Romanian cv. Fundulea F201R (1B and 5A) and the French cv. Renan (5AL) were screened with 17 SSRs. No National List cultivar had haplotypes similar to any of these QTL. However, the highly resistant German reference cultivar Petrus had an identical haplotype to cv. Fundulea F201R on 1B indicating that this cultivar has an allelic FHB resistance QTL at that location.     

Quantitative trait loci for resistance to fusarium head blight and deoxynivalenol accumulation in Wangshuibai wheat under field conditions

Wangshuibai is a Chinese landrace wheat with a high level of resistance to fusarium head blight (FHB) and deoxynivalenol (DON) accumulation. Using an F7 population of recombinant inbred lines (RILs) derived from the cross between Wangshuibai and Annong 8455 for molecular mapping of quantitative trait loci (QTL) for FHB resistance, the proportion of scabbed spikelets (PSS) and DON content were assessed under field conditions. Composite interval mapping revealed that two and three QTL were significantly associated with low PSS and low DON content, respectively, over 2 years. QTL on chromosomes 3B and 2A explained 17 and 11·5%, respectively, of the phenotypic variance for low PSS, whereas QTL on chromosomes 5A, 2A and 3B explained 12·4, 8·5 and 6·2%, respectively, of the phenotypic variance for low DON content. The 3B QTL appeared to be associated mainly with low PSS, and the 5A QTL primarily with low DON content in Wangshuibai. The 2A QTL had minor effects on both low PSS and DON content. Microsatellite and AFLP markers linked to these QTL should be useful for marker-assisted selection of QTL for low PSS and low DNA content from Wangshuibai.     

Biological control of fusarium seedling blight disease of wheat and barley

ABSTRACT Fusarium fungi, including F. culmorum, cause seedling blight, foot rot, and head blight diseases of cereals, resulting in yield loss. In a screen for potential disease control organisms and agents, Pseudomonas fluorescens strains MKB 100 and MKB 249, P. frederiksbergensis strain 202, Pseudomonas sp. strain MKB 158, and chitosan all significantly reduced the extent of both wheat coleoptile growth retardation and wheat and barley seedling blight caused by F. culmorum (by 53 to 91%). Trichodiene synthase is a Fusarium enzyme necessary for trichothecene mycotoxin biosynthesis; expression of the gene encoding this enzyme in wheat was 33% lower in stem base tissue coinoculated with Pseudomonas sp. strain MKB 158 and F. culmorum than in wheat treated with bacterial culture medium and F. culmorum. When wheat and barley were grown in soil amended with either chitosan, P. fluorescens strain MKB 249, Pseudomonas sp. strain MKB 158, or culture filtrates of these bacteria, the level of disease symptoms on F. culmorum-inoculated stem base tissue (at 12 days post- F. culmorum inoculation) was >/=31% less than the level on F. culmorum-inoculated plants grown in culture medium-amended soil. It seems likely that at least part of the biocontrol activity of these bacteria and chitosan may be due to the induction of systemic disease resistance in host plants. Also, in coinoculation studies, Pseudomonas sp. strain MKB 158 induced the expression of a wheat class III plant peroxidase gene (a pathogenesis-related gene).     

Five-year survey uncovers extensive diversity and temporal fluctuations among fusarium head blight pathogens of wheat and barley in Brazil

We conducted a five-year survey (2011–2015) of barley and wheat fields in Paraná state, Brazil, obtaining 754 Fusarium isolates from spikes with fusarium head blight (FHB)-symptoms. Multilocus genotyping and TEF-1α gene sequence analyses confirmed the dominance of the F. graminearum species complex (FGSC, 75.7%), but F. poae (11.5%), as well as F. avenaceum and related members of the F. tricinctum species complex (FTSC, 8.1%) appeared as substantial contributors to FHB. Within the FGSC, F. graminearum of the 15-ADON genotype was dominant (63%), followed by F. meridionale of the NIV genotype (23.1%), F. cortaderiae of the NIV (7%) or 3-ADON (2.6%) genotypes, and F. austroamericanum (3.8%) of the 3-ADON genotype. Substantial variation in pathogen composition was observed across years, with F. poae and F. meridionale frequencies significantly elevated in some years. Most F. poae strains produced DAS, diANIV, and butenolide, but not neosolaniol, T-2, or HT-2. All FTSC species produced moniliformin. Enniatin production was widespread among FTSC species, with the single F. acuminatum strain found to be the strongest producer of enniatins. Our findings confirm FGSC as a major contributor to FHB and expand considerably our knowledge of the presence, frequency, and conditions under which other pathogens may emerge, altering the spectrum of toxins that may accumulate in grain.     

Integrated control of fusarium head blight and deoxynivalenol mycotoxin in wheat

Fusarium head blight (FHB), a devastating disease that affects wheat, is caused by a complex of Fusarium species. The overall impact of Fusarium spp. in wheat production arises through the combination of FHB and mycotoxin infection of the grain harvested from infected wheat spikes. Spike infection occurs during opening of flowers and is favoured by high humidity or wet weather accompanied with warm temperatures. Available possibilities for controlling FHB include the use of cultural practices, fungicides and biological approaches. Three cultural practices are expected to be of prime importance in controlling FHB and the production of mycotoxins: soil preparation method (deep tillage), the choice of the preceding crop in the rotation and the selection of appropriate cultivar.     

The Brachypodium distachyon UGT Bradi5gUGT03300 confers type II fusarium head blight resistance in wheat

Fusarium head blight (FHB), caused by fungi belonging to the Fusarium genus, is a widespread disease of wheat (Triticum aestivum) and other small-grain cereal crops. The main causal agent of FHB, Fusarium graminearum, produces mycotoxins mainly belonging to type B trichothecenes, such as deoxynivalenol (DON), that can negatively affect humans, animals and plants. DON detoxification, mainly through glucosylation into DON-3-O-glucose, has been correlated with resistance to FHB. A UDP-glucosyltransferase from the model cereal species Brachypodium distachyon has been shown to confer resistance both to initial infection and to spike colonization (type I and type II resistances, respectively). Here, the functional characterization of transgenic wheat lines expressing the Bradi5g03300 UGT gene are described. The results show that, following inoculation with the fungal pathogen, these lines exhibit a high level of type II resistance and a strong reduction of mycotoxin content. In contrast, type I resistance was only weakly observed, although previously seen in B. distachyon, suggesting the involvement of additional host-specific characteristics in type I resistance. This study contributes to the understanding of the functional relationship between DON glucosylation and FHB resistance in wheat.     

Fusarium species and chemotypes associated with fusarium head blight and fusarium root rot on wheat in Sardinia

Environmental conditions in Sardinia (Tyrrhenian Islands) are conducive to fusarium root rot (FRR) and fusarium head blight (FHB). A monitoring survey on wheat was carried out from 2001 to 2013, investigating relations among these diseases and their causal agents. FHB was more frequently encountered in the most recent years while FRR was constantly present throughout the monitored period. By assessing the population composition of the causal agents as well as their genetic chemotypes and EF‐1α polymorphisms, the study examined whether the two diseases could be differentially associated to a species or a population. Fusarium culmorum chemotypes caused both diseases and were detected at different abundances (88% 3‐ADON, 12% NIV). Fusarium graminearum (15‐ADON genetic chemotype) appeared only recently (2013) and in few areas as the causal agent of FHB. In F. culmorum, two haplotypes were identified based on an SNP mutation located 34 bp after the first exon of the EF‐1α partial sequence (60% adenine, 40% thymine); the two populations did not segregate with the chemotype but the A‐haplotype was significantly associated with FRR in the Sardinian data set (P = 0·001), suggesting a possible fitness advantage of the A‐haplotype in the establishment of FRR that was neither dependent on the sampling location nor the sampling year. The SNP determining the Sardinian haplotype is distributed worldwide. The question whether the A‐haplotype segregates with characters facilitating FRR establishment will require further validation on a specifically sampled international data set.     

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.     

Allocation of resources: sources of variation in fusarium head blight screening nurseries

ABSTRACT Severe epidemics of Fusarium head blight (FHB) caused by Fusarium graminearum, group II (teleomorph: Gibberella zeae) have been occurring on wheat crops in the northcentral United States and southern Canada. Evaluation of resistance to FHB is difficul, because resistance is partial and infection depends upon host plant maturity. Variance component analysis was conducted to determine how best to allocate resources among environments, replications, and subsamples (heads per plot) in FHB screening nurseries. Advanced breeding lines from the Ohio State University wheat-breeding program were evaluated in screening nurseries from 1995 to 1997. Nurseries were artificially inoculated and sprinkler-irrigated to induce FHB epidemics. Over 80% of the variation within an environment resulted from variation associated with subsampling individual heads within plots. The second greatest source of variation was due to genotype by replication interactions. Host plant maturity influenced disease ratings in 1997. The repeatability of genotype means was approximately 50% within environments. The greatest reduction in genotype standard errors was obtained through additional environments, and then replications. Because the cost of an additional environment was estimated at five times the cost of an additional replication, the most cost-effective improvement in precision was obtained through the addition of replications. Advanced breeding lines should be evaluated in at least four replications per environment. Segregating populations will require more replications.     

Spatial variability of fusarium head blight pathogens and associated mycotoxins in wheat crops

The spatial pattern of Fusarium‐infected kernels and their mycotoxin contamination was studied in four wheat fields in Germany using geo‐referenced sampling grids (12–15 × 20–30 m, 28–30 samples per field) at harvest. For each sample, frequency of Fusarium‐infected kernels and spectrum of species were assessed microbiologically; mycotoxin contents were determined by HPLC‐MS/MS analysis. Spatial variability of pathogens and mycotoxins was analysed using various parameters including Spatial Analysis by Distance IndicEs (sadie^® ). Microdochium majus, the most frequent head blight pathogen in 1998, was less frequent in 1999 and could not be detected in kernels from two fields in 2004. Fusarium avenaceum, F. graminearum and F. poae were the most frequent Fusarium species, with 7–8 species per field. The frequency of Fusarium‐infected kernels was 3–15% and the incidence of species showed considerable within‐field variability. Spatial patterns varied among Fusarium species as well as from field to field. Although pathogens and mycotoxin were often distributed randomly in the field, F. avenaceum, F. graminearum, F. poae, F. sporotrichioides, F. tricinctum and the mycotoxin moniliformin had an aggregated pattern in at least one field. Patterns are discussed in relation to spread of Fusarium species depending on inoculum sources, spore type, kind of dispersal, availability of susceptible host tissue and micro‐climate. Sampling of wheat fields for representative assessment of mycotoxins is complicated by random patterns of Fusarium‐infected kernels, especially where the frequency of infection is small.     

戊唑醇与叶菌唑对小麦赤霉病的防治效果

小麦赤霉病是我国小麦产区的主要病害。种植抗病品种是防治该病最经济有效的方法,但由于小麦对赤霉病的抗性属水平抗性,受环境影响比较大,难以抵抗病菌的侵染危害。因此,防治赤霉病最有效的方法是化学防治。我国目前防治赤霉病的药剂以多菌灵为主,已有报道赤霉病菌对多菌灵产生了抗药性,所以筛选新型的杀菌剂用于小麦赤霉病