Comparison of commercial European wheat cultivars to Fusarium infection of head and seedling tissue

Susceptibility of eight commercial European wheat cultivars to fusarium head blight (FHB) disease caused by Fusarium graminearum , F. culmorum , F. poae and Microdochium nivale (formerly known as Fusarium nivale ) was compared under controlled environment conditions (16°C). FHB did not differentially affect cultivars in terms of disease symptoms, fungal DNA content of grain or deoxynivalenol (DON) contamination. However, the Hungarian-grown cultivars GK-Othalom and Fatima 2 (of Romanian origin) showed greater type V resistance (yield tolerance) to FHB than did the others. Also, nivalenol was produced by F. poae in these two cultivars and in Italian cultivar Norba, but not in other cultivars. Overall, significant relationships were found between the FHB and seedling blight resistance in vitro of these eight cultivars, but such relationships were generally highly dependent on cultivar, and therefore it is likely that the in vitro test is at best measuring components of FHB resistance and/or genotype-specific resistance components.     

Towards the Development of a Novel In Vitro Strategy for Early Screening of Fusarium Ear Blight Resistance in Adult Winter Wheat Plants

A novel in vitro bioassay is described for screening Fusarium ear blight (FEB) resistance in adult winter wheat plants. Seven winter wheat cultivars were assessed for components of partial disease resistance as 28 day-old detached leaf segments in the laboratory using isolates of Microdochium nivale var. nivale and M. nivale var. majus. Results were compared with disease data obtained at anthesis using the same cultivars as whole plants and the same isolates under glasshouse conditions. Significant cultivar differences were observed using detached leaves, with cv. Avalon (a Fusarium culmorum ear susceptible cultivar) having the shortest leaf incubation period, greatest leaf lesion development and shortest leaf latent period compared to cv. Spark (a Fusarium culmorum ear resistant cultivar), which had the longest leaf incubation period, least leaf lesion development and longest leaf latent period. Using whole plants, cv. Avalon had the shortest ear incubation period and greatest ear disease severity, whilst cv. Spark had the longest incubation period and least ear disease severity. Overall, cultivars of intermediate F. culmorum ear resistance expressed intermediate responses to M. nivale isolates, using both detached leaves and whole plants. Significant correlations were found with ear disease severity and ear incubation period in whole plants and components of partial disease resistance in detached leaves, with significant correlations obtained between leaf incubation period and ear disease parameters using the M. nivale var. nivale isolate. In addition, leaf latent period and leaf lesion size showed significant correlations with whole plant reactions using M. nivale var. nivale and var. majus isolates. The in vitro screening of cultivars as detached leaves using M. nivale isolates may offer a real possibility of a rapid bioassay for the early screening of FEB resistance in wheat and other cereals.     

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).     

The contribution of ground-level inoculum of Fusarium culmorum to ear blight of winter wheat

In a series of field experiments in eastern England over 5 years, severe ear blight developed only in plots of winter wheat that were inoculated by spraying with conidial suspensions of Fusarium culmorum during anthesis, and in which infection was encouraged by rainfall or mist irrigation. In the absence of artificial inoculation of the ears, F. culmorum caused less extensive ear blight, and only where soil-surface inoculum was available after its application on infested plant material (colonized oat grains) up to 3–4 weeks before anthesis; it then developed most where significant rainfall occurred close to the time of anthesis. A warm, dry period following application of inoculum to the ground in late March contributed to increased infection of grain by F. culmorum , although ear blight was not increased. Ear infection therefore depended on adequate viable inoculum on infested plant debris within the crop, and conditions tending to favour brown foot rot development as well as, subsequently, rainfall and moist conditions during anthesis. These conditions did not occur together naturally during this period. Seedling infection by F. culmorum or Microdochium nivale made no significant contribution to ear blight. Inoculation of ears at anthesis with M. nivale or a locally obtained isolate of F. langsethiae did not produce ear blight symptoms. Possibilities for minimizing the availability of inoculum of F. culmorum and the implications for various options for ear-blight control are discussed.     

Fusarium ear blight (scab) in small grain cereals—a review

This review of Fusarium ear blight (scab) of small grain cereals has shown that up to 17 causal organisms have been associated with the disease, which occurs in most cereal-growing areas of the world. The most common species were Fusarium graminearum (Gibberella zeae), F. culmorum, F, avenaceum (G, avenacea), F, poae and Microdochium nivale (Monographella nivalis). The disease was recorded most frequently under hot, wet climatic conditions where significant yield losses and mycotoxin accumulation in grain were reported. Possible sources of inoculum were reported as crop debris, alternative hosts and Fusarium seedling blight and foot rot of cereals. The mode of dispiersal of inoculum to ears remains unclear, but contaminated arthropod vectors, systemic fungal growth through plants, and wind and rain-splash dispersal of spores have been proposed. Infection of wheat ears was shown to occur mainly during anthesis, and it has been demonstrated that fungal growth stimulants may be present in anthers. Despite the importance of the disease, particularly during epidemic years, control methods are limited. Much effort has gone into breeding resistant wheat varieties and into improving our understanding of the possible mechanisms and genetic basis of resistance, with only moderate success. There are also surprisingly few reports of successful fungicidal or biological control of the disease in the field.     

Population Dynamics of Fusarium spp. and Microdochium nivale in Crops and Crop Residues of Winter Wheat

ABSTRACT Naturally occurring populations of Fusarium avenaceum, F. culmorum, F. graminearum, F. poae, and Microdochium nivale were studied in two field experiments from anthesis in June 2003 until harvest in crops of winter wheat, and subsequently during 10 months after harvest until June 2004 on their residues exposed on the soil surface under field conditions. The dynamics of the different pathogens were estimated by quantifying the amount of DNA present in wheat tissues using TaqMan-polymerase chain reaction. While colonization of grain by Fusarium spp. and M. nivale was low, high amounts of DNA of F. avenaceum, F. graminearum, and F. culmorum were found in ear residues, internodes, and nodes of the mature crop. Amounts of DNA of pathogens decreased significantly during the following 10 months in residues of internodes and nodes, but not in residues of stem bases. Knowledge on population dynamics of pathogens will help to develop preventive measures aimed at reduction of inoculum sources of head blight pathogens.     

Fusarium ear blight of wheat: the use of quantitative PCR and visual disease assessment in studies of disease control

Quantitative PCR analysis and visual disease assessment (VDA) were used to study Fusarium culmorum and F. poae ear blight of wheat and its fungicidal control in three glasshouse trials (1994–5 and 1996–7). VDA indicated high levels of both diseases in the trials, while PCR analysis showed that the amounts of F. poae detected in infected plants were low relative to the amounts detected for F. culmorum . PCR and VDA analysis both indicated that the demethylase-inhibiting (DMI) fungicides prochloraz and tebuconazole significantly decreased F. culmorum and F. poae ear blight. The PCR results, however, revealed levels of disease control by fungicide treatments that were consistently higher than those suggested by VDA. Overall, both fungicides appeared equally effective in controlling the two pathogens. PCR and VDA analysis indicated that the anilino-pyrimidine fungicide pyrimethanil had no significant effect on F. culmorum ear blight. Correlations between VDA at cereal growth stage 80 and PCR analysis were similar for F. culmorum and F. poae . Yield analysis, as measured by 1000 grain weight, indicated that DNA content more accurately predicted yield loss than did VDA scores. Inoculation with F. culmorum significantly reduced yield and significant relationships were observed between F. culmorum disease (as assessed visually or by PCR) and yield, with yield decreasing as disease increased. In contrast, inoculation with F. poae had no significant effect on yield and no significant relationships were observed between F. poae disease and yield. These results have important implications for field studies of Fusarium ear blight of wheat because they highlight the importance of identification of the causal organisms to the species level.     

Performance of the Pseudomonas chlororaphis biocontrol agent MA 342 against cereal seed-borne diseases in field experiments

The bacterial biocontrol agent Pseudomonas chlororaphis, strain MA 342, was tested for activity against a number of cereal seed-borne diseases in a total of 105 field experiments carried out at different locations in Sweden during the years 1991-1996. Bacterial liquid culture was directly applied to pathogen-infested seeds of barley, oats, wheat and rye without additives. The seeds were then dried and sown in field together with fungicide-treated and untreated seeds used as controls. The bacterization controlled seed-borne diseases caused by Drechslera (Pyrenophora) graminea, D. teres, D. avenae, Ustilago avenae, U. hordei, and Tilletia caries, as effectively as guazatine + imazalil, and these effects were consistent over the years and over varying climatic zones. Diseases caused by pathogens like U. nuda, soil-borne T. caries and T. contraversa were not controlled and the bacterization gave less than full effect against diseases caused by Microdochium (Fusarium) nivale, and Bipolaris sorokiniana (Cochliobolus sativus). Bacterized seeds could be stored dry for at least two years without losing the disease suppressing effect of the bacterial treatment, when tested in the field.     

Comparison of pathogenicity of the Fusarium crown rot (FCR) complex (<Emphasis Type="Italic">F. culmorum</Emphasis>, <Emphasis Type="Italic">F. pseudograminearum</Emphasis> and <Emphasis Type="Italic">F. graminearum)</Emphasis> on hard red spring and durum wheat

Fusarium species involved in the Fusarium crown rot (FCR) complex affect wheat in every stage of development from seedling to grain fill. This study was designed to compare the aggressiveness of the FCR complex members including F. culmorum, F. pseudograminearum and F. graminearum in causing seedling blight, decreased plant vigour and crown rot. To assess their relative pathogenicity, two hard red spring wheat cultivars and two durum wheat cultivars were inoculated in the field with five isolates from each of the three species for two years. Significant differences in patterns of pathogenicity were identified. In particular, F. culmorum caused greater seedling blight while F. pseudograminearum and F. graminearum caused greater crown rot. Greatest yield reductions were caused by F. pseudograminearum. Cultivar differences were identified with respect to seedling disease and late season crown rot. No interactions were identified between cultivar performance and isolates or species with which they were challenged.     

The use of species-specific PCR-based assays to analyse Fusarium ear blight of wheat

Polymerase chain reaction (PCR) assays for the detection of various Fusarium species and Microdochium nivale subspecies were compared with conventional visual disease assessment using a field plot of wheat in which the central subplot was inoculated with F. culmorum . Visual disease assessment was performed on a range of samples taken from each of 15 subplots at growth stage 80. At harvest, each sample was divided into its component parts, i.e. grain, glume and rachis, and species-specific PCR analysis was used to detect the presence of F. culmorum , F. poae , F. avenaceum , F. graminearum , M. nivale var. majus and M. nivale var. nivale . Within the inoculated subplot there was good correlation between visual disease assessment and PCR analysis, both techniques indicating a high incidence of F. culmorum in this region. According to the visual disease assessment results, there was also a relatively high incidence of F. culmorum in most other regions of the field plot. However, according to PCR analysis the incidence of F. culmorum in many of the other subplots was relatively low and F. poae , M. nivale var. majus and var. nivale , and F. avenaceum were detected within the grain, glume and rachis tissues of many of the ear samples from these subplots. F. poae predominated in the glume component of ears and M. nivale var. majus and var. nivale in the rachis component. M. nivale PCR results revealed that 64% of infected samples involved var. majus , and 36% var. nivale . PCR analysis has highlighted some difficulties that may arise when using visual assessment for studying disease complexes.     

Survey of benomyl resistance in Fusavium species on winter wheat in England and Wales in 1986

In 1986, samples from 109 winter wheat crops in England and Wales were examined for benomyl resistance in Fusarium species. Of the 704 isolates obtained, 581 were identified as Fusarium nivale, of which 92.1 % were resistant to benomyl. Of the remaining isolates, 82 were identified as F. avenaceum, 40 as F. culmorum and one as F. poae; none of these isolates were resistant to benomyl. The vast majority of isolates of Fusarium spp. were obtained from superficial nodal or internodal lesions on the stems.     

Biocontrol of seedling diseases of barley and wheat caused by Fusarium culmorum and Bipolaris sorokiniana: effects of selected fungal antagonists on growth and yield components

The purpose of this study was to verify, under natural conditions, biological control effects obtained in a former screening programme against Fusarium culmorum. The most successful antagonists against seedborne Fusarium culmorum and Bipolaris sorokiniana were isolates of Chaetomium sp., Idriella bolleyi and Gliocladium roseum. These results were also obtained when the antagonists were applied to B. sorokiniana-infected barley sown in field soil in pots. In field experiments, G. roseum gave the best control of F. culmorum in winter wheat. One month after sowing, germination increased by 170%, the disease index decreased by 73% and plant dry weight increased by 25%, compared to untreated plots. At harvest, the number of tillers per row was found to have increased by 53%, yield had increased by 160% and the 1000-grain weight had increased by 4%. For all evaluated parameters the effect was significantly different from the untreated plots and not significantly different from the plots treated with the fungicide, Sibutol LS 280. I. bolleyi gave a lower but still significantly effective control, when evaluated for disease index and numbers of tillers per row, while Chaetomium sp. did not show any reduction in the disease. Furthermore, in field experiments using barley infected with B. sorokiniana , a significant effect of G. roseum was demonstrated as increased plant dry weight after 1 month and increased 1000-grain weight at harvest. The disease-controlling effect of G. roseum on F. culmorum was shown in a field experiment with spring barley.     

The incidence of Fusarium spp. in stem bases of selected crops of winter wheat in the Midlands, UK

The incidence of pathogenic Fusarium and Microdochium species in stem bases of winter wheat was investigated in a total of nine crops in 3 years, i.e. 1987, 1988 and 1989. Four Fusarium species were isolated: F. nivale ( = Microdochium nivale ), F. avenaceum , F. culmorum and F. graminearum . The predominant species was F. nivale followed by F. avenaceum and F. culmorum . Isolations of F. graminearum were made only from shoots collected during August 1989. The highest incidence of F. nivale occurred during April 1989 in the cultivar Brock when the fungus was isolated from 65% of the shoots sampled. The highest incidence of F. avenaceum was 60% (August 1988, cv. Slejpner) and F. culmorum 37% (August 1989, cv. Mercia). A delay in the isolation of Fusarium spp. during 1987 was attributed to the low January temperatures, and an upsurge of F. culmorum and F. graminearum during 1989 to the warm dry summer. The incidence of F. nivale fluctuated during the 1988 and 1989 seasons, particularly during spring. The effects of fungicide spray programmes and the growth and development of the wheat crop are discussed as possible contributory factors to this.     

Fungicide seed treatment efficacy against Microdochium nivale and M. majus in vitro and in vivo

BACKGROUND: Seed-borne Microdochium majus (Wollenweber) and M. nivale Fries are the primary pathogens responsible for Fusarium seedling blight in the UK. The two species show differences in pathogenicity, host preference and sensitivities to temperature, but their relative sensitivities to fungicide seed treatments are unknown. The aim was firstly to determine the efficacy of fungicide seed treatments towards single-spore isolates of M. majus and M. nivale using in vitro experiments, and subsequently to determine efficacy in vivo over a range of temperatures. RESULTS: Differences in EC(50) values between all seed treatments were evident from the in vitro experiments and ranged from 0.028 mg L(-1) for fludioxonil to 22.8 mg L(-1) for carboxin + thiram. The two seed treatments that showed best performance in vitro were used to examine efficacy towards seed-borne infection in vivo at 4, 8, 12 and 16 degrees C. Generally, seedling emergence improved and the severity of stem-base disease symptoms on emerged seedlings was reduced for both species through the use of the fungicides. The combination of fludioxonil + difenconazole showed improved performance compared with fludioxonil alone. Significantly less severe symptoms were observed through the use of fludioxonil and fludioxonil + difenconazole compared with bitertanol + fuberidazole at 12 degrees C and for all except one M. nivale infected seed lot at 8 degrees C. CONCLUSIONS: Differences in fungicide sensitivity between the two species in vitro were not evident in vivo. This is the first report of the effect of fungicide seed treatments on the control of seedling blight caused by M. majus and M. nivale.     

Screening for fungal antagonists of seed-borne Fusarium culmorum on wheat using in vivo tests

A screening system is described for identifying fungal antagonists from soil which are effective in controlling seed-borne Fusarium culmorum on wheat (T. aestivum L.). The procedure comprised three consecutive in vivo tests done under controlled conditions using three different plant growing media. Altogether 1701 fungal isolates from Finnish field soils were screened for biocontrol activity. 210 fungal isolates that had advanced to various stages in the screening system were also included in a field experiment. The isolates that were the most effective in controlling seedling blight under natural conditions belonged to the genus Gliocladium. The screening tests separated Gliocladium spp. rather clearly from the rest of test fungi and thus the overall agreement among the results was good. The assays run under controlled conditions did not efficiently predict which of the Gliocladium isolates would be best in protecting wheat seedlings under field conditions.     

Fusarium head blight of cereals in Denmark: species complex and related mycotoxins

Quantitative real-time polymerase chain reaction differentiating 10 Fusarium spp. and Microdochium nivale or M. majus was applied to a total of 396 grain samples of wheat, barley, triticale, oat, and rye sampled across Denmark from 2003 to 2007, along with selected samples of wheat and barley from 1957 to 2000, to determine incidence and abundance of individual Fusarium spp. The mycotoxins deoxynivalenol (DON), nivalenol, zearalenone, T-2, and HT-2 were quantified using liquid chromatography-double mass spectrometry. Major differences in the Fusarium species complex among the five cereals as well as great yearly variation were seen. Fusarium graminearum, F. culmorum, and F. avenaceum were dominant in wheat, with DON as the dominant mycotoxin. F. langsethiae, F. culmorum, and F. avenaceum were dominant in barley and oat, leading to relatively high levels of the mycotoxins T-2 and HT-2. F. graminearum, F. culmorum, and F. avenaceum dominated in triticale and rye. The nontoxigenic M. nivale/majus were present in significant amounts in all cereal species. Wheat and barley samples from 1957 to 1996 exhibited no or very low amounts of F. graminearum, indicating a recent increase of this pathogen. Biomass and mycotoxin data exhibited good correlations between Fusarium spp. and their corresponding mycotoxins under field conditions.     

Stem-base disease and fungal colonisation of winter wheat grown in compost inoculated with Fusarium culmorum, F. graminearum and Microdochium nivale

Fungal colonisation of winter wheat cv. Cadenza by Fusarium culmorum, F. graminearum and Microdochium nivale was studied under conditions designed to avoid the splash dispersal of conidia from infested compost, to evaluate the possibility that systemic growth may transfer infection from the stem-base to the head. At decimal growth stages 33, 59, 77–87 and 95 the extent of fungal growth was assessed using a sample of 72 plants, by the recovery of fungal species from the stem-base, from each node and from the ear. Each of the fungi was recovered from stem tissues above soil level in some, apparently symptomless, plants. Symptoms of Fusarium foot rot were seen in an increasing proportion of plants during grain-fill and desiccation. There was an inverse relationship between recovery and the height above stem-base from which the stem tissue was excised. F. culmorum was the most frequently isolated fungus and it was also recovered from the highest position in plants. Only 3% of plants were colonised above the second node and none of the fungal species were recovered from either the fifth node or the ear. This suggests that colonisation and systemic growth from Fusarium infested compost is unlikely to contribute to the development of ear blight symptoms in winter wheat.     

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).     

Restriction fragment length polymorphism analysis of variation in Fusarium species causing ear blight of cereals

Genetic variation in Fusarium species on wheat was investigated using restriction fragment length polymorphism (RFLP) analysis. Single-spore lines (76) of Fusarium were recovered from 24 ears of wheat in a field plot exhibiting severe symptoms of Fusarium ear blight and identified using classical taxonomic criteria. Four Fusarium species were present, of which F. avenaceum and F. culmorum were predominant with F. lateritium and F. poae present in two ears and one ear, respectively. RFLP analysis using rDNA (pTA71) or total genomic DNA from an F. culmorum isolate clearly distinguished the four species. Genetic fingerprints of the isolates generated using DNA of bacteriophage M13 (which contains a mini-satellite repeat sequence) revealed considerable variation within three of the four species (except F. poae). Generally, only a single clone was recovered from each ear and in all but one case only a single species was obtained from each spikelet. However, in several instances it appeared that more than one clone of a species was present within a single spikelet.     

Comparison of visual head blight ratings, seed infection levels, and deoxynivalenol production for assessment of resistance in cereals inoculated with Fusarium culmorum

Seven spring wheat, 13 barley, 14 oats and 20 winter wheat genotypes were inoculated at flowering in 1993 and 1994 with mixed conidial suspensions of 8 isolates of Fusarium culmorum. Four weeks after inoculation, head blight was recorded in the field. After harvest, seed infection was assessed by a Freezing Blotter Test in the laboratory. Seed samples were also analyzed for deoxynivalenol (DON) content. Differences were found in head blight rating, the levels of infected seeds and the DON content between wheat, barley, and oats and between cultivars. Highly significant correlations were found between the percentage of heavily infected seed and the DON content. The weighted mean value of infected seeds and DON content were also significantly correlated. No significant correlation was found between head blight rating in the field and DON content. The level of infected seeds, as determined by the Freezing Blotter Test, was a better indication of the DON content in the seeds than the head blight rating. This visual assessment of levels of infected seeds gives a reliable estimate of resistance to Fusarium.