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The 2nd International Symposium on Fusarium Head Blight Orlando, Florida, USA.
11-15th December 2004 For the uninitiated, Fusarium head blight (FHB) is a disease of wheat and other cereals that is caused by Fusarium species, predominantly F. graminearum and F. culmorum. The disease is also known as Fusarium ear blight or scab and is of particular significance because trichothecene mycotoxins, produced by the fungus during colonisation, are harmful to human and animal consumers. The most prevalent of these mycotoxins are deoxynivalenol (DON) and nivalenol (NIV) although other, more toxic compounds, are produced by some of the Fusarium species associated with FHB.
The First International Symposium had taken place in Suzhou, China in 2000. The choice of venue had been most appropriate as this was the origin of the wheat variety Sumai3, which is the source of FHB resistance most utilised in plant breeding programmes around the world. The venue of the 2nd International Symposium could boast no similar claim, but did provide an excellent environment and facilities for the 320 delegates who descended upon Orlando for this meeting. The symposium brought together, from across the globe, scientists who have significant research interests in FHB. It provided a unique opportunity to hear, first hand, from those working in diverse areas relating to this disease. The breadth of the conference provided a holistic view of FHB, from incidence, effects and control, through to forecasting and food safety, including political considerations related to consumer risks. Attendance at this symposium provided an opportunity to present our FHB work to a global audience and to stimulate dialogue and collaboration with researchers who may have been known previously only as names on scientific publications. Most importantly, the symposium brought together scientists from Europe, USA and elsewhere and enabled them to identify areas for potential collaboration as well as aspects that require concerted effort if this disease is to be effectively controlled.
The conference opened with a presentation by Richard Emerson of Busch Agricultural Resources, USA who described the impact of this disease on the USA malting and brewing industry. As FHB took hold in the USA, affected regions became unsuitable for producing malting barley and malting houses also relocated to minimise the length of transport chains. The industry does not accept any detectable DON in grain used for malting and brewing. It appears that the brewing industry wishes to have only a single toxin in its product!
This reminder of the impact of this disease on one part of the food and feed chain was followed by the Plenary Session, consisting of three presentations.
Bikram Gill of Kansas State University began with a talk centring upon the cereal hosts. This presentation described the genetic similarities between cereals, including conservation of synteny across rice, wheat, barley and other cereal crops.
These similarities have been exploited in the generation of genetic maps and the use of comparative genetics. Within wheat, cytogenetic stocks have been used extensively to identify the location of genes. Currently, expressed sequence tags (ESTs) are being mapped onto lines carrying known deletions on specific chromosomes which allows the ESTs to be assigned to ‘bins’ that correspond to particular parts of chromosomes.
Thus, where mapping indicates that genes for resistance are located in particular regions, candidate resistance genes can immediately be identified from within the relevant ‘bin’. Other resources that have been developed will aid efforts to clone genes from wheat, including those responsible for resistance to FHB. Large insert-size DNA (bacterial artificial chromosome (BAC)) libraries have been produced to enable map-based cloning approaches to be undertaken. The recently released Affymetrix GeneChip for wheat will permit the expression of 1000’s of genes to be monitored in response to infection by Fusarium species to identify those associated with resistance/susceptibility.
These resources should contribute greatly to understanding the basis of resistance/susceptibility of wheat and other cereals to FHB.
The second talk centred upon genomics of F. graminearum and was given by Corby Kistler of USDA-ARS. He described the production of the recently assembled first-draft of the genome sequence of this fungus. Annotation is being improved by reference to F. graminearum ESTs identified by researchers world-wide. An Affymetrix Gene-Chip has also been produced for this fungus and this tool will enable in-depth investigation of gene regulation within F. graminearum during colonisation of hosts and during the saprophytic phase of the life-cycle of this fungus. He also described research to produce mutants within F. graminearum with which to identify genes associated with pathogenicity and virulence of this fungus.
The final talk of this session was presented by Paul Nicholson, who brought together the partners involved in this disease and gave an overview of the current state of knowledge of the host-pathogen interaction and, perhaps more importantly, what is not known. This presentation also highlighted aspects of pathogen-pathogen interactions in FHB.
In those regions where toxin-producing and non-toxin producing species form disease complexes the competitive interactions between pathogens has important consequences for disease and subsequent risks to consumers associated with the consumption of mycotoxin contaminated cereals or their products. While genomics and molecular diagnostic tools are beginning to shed light on some of the host-pathogen and pathogen-pathogen interactions much remains to be learned. Further insights into the study of FHB and progress towards controlling this disease were forthcoming in subsequent sessions.
The second session focussed on host plant resistance and variety development. Durable natural resistance in host cereals is the most cost effective and appealing disease control strategy for FHB.
Keeping this in consideration and the fact that variety development in the United States is carried out primarily by research labs at universities and USDA stations, this research session was allocated the most time for talks and poster presentations. A plenary talk by Maarten van Ginkel from CIMMYT, Mexico and Tomohiro Ban from CIMMYT-JIRCAS kicked off the proceedings. Their talk centred on global progress in identifying and deploying resistance genes against FHB. They stressed that FHB resistance is a polygenic trait and several QTLs have been identified that contribute to resistance.
Maarten van Ginkel highlighted a range of factors that needed to be considered while developing FHB resistance varieties such as multiple alleles, linkage disequilibrium, pleitropy and epistatic gene effects.
Tomohiro Ban continued the talk summarising key QTLs associated with different components of the host plant’s defence arsenal against FHB.
Jim Anderson from the University of Minnesota presented an update on the quest to clone the gene or genes responsible for the best FHB resistance characterised so far, residing on the short arm of chromosome 3 (3BS). He stressed that the main strategy for elucidating the molecular genetics of FHB resistance was to locate molecular markers that segregated closely or were linked to the resistance gene of interest. His results showed that the QTL was thought to lie in an interval spanning 0. 5cM and the group were developing markers to clone and identify the gene. Hermann Buerstmayr from IFA-Tulln, Austria and Hirokazu Honda from the National Institute of Agrobiological Sciences, Japan both gave stimulating talks about the progress on mapping FHB resistance QTLs, giving a European and South Asian perspective respectively. Daryl Somers from Agri-Food Canada presented similar progress in Canada and highlighted strategies to introgress resistance QTLs in breeding lines. Six other talks were included in this session covering resistance to the mycotoxin deoxynivalenol, FHB resistance in European wheat breeding programs, utilisation of alien translocation lines to introgress novel QTLs, and progress in identifying FHB resistance QTLs in barley.
The third session focussed on genetic engineering.
There were six talks in this session arguing the case for transgenic control of FHB with interesting strategies. Stephen Baenziger from the University of Nebraska got the ball rolling with a plenary talk on wheat transformation. He highlighted the relative difficulty in transforming a hexaploid genome of over 16000mb, but argued that Agrobacterium mediated transformation could be employed to increase the frequency of gene integration events, and presented work on incorporating anti-fungal proteins and inhibitors of programmed cell death to enhance FHB resistance. Ron Skadsen from the USDA labs in California gave an interesting talk on the use of host tissue specific promoters that could be designed to target anti-fungal gene expression during the short window of Fusarium infection. Jyoti Shah from Kansas State University discussed the successful incorporation of an arabidopsis resistance gene in wheat that increased FHB resistance. Other talks in this session further highlighted transgenic approaches to combat FHB.
Session four focused on the use of chemical, cultural and biological control for reducing the effects of FHB. The main point to come from this session, one emphasised by all speakers, was that an integrated control strategy was the one most likely to be succeed. The session opened with Friedrich Kerz-Mohlendick (Bayer CropSciences Ag) describing the control achieved using DMI (demethylation inhibitors) fungicides, in particular the new active prothioconazole. Philip Jennings (Central Science Laboratory, UK) continued on the fungicide theme by looking at the effect of timing and application rate on fungicide efficacy. He indicated that optimum control could be achieved if an appropriate product was used at the manufacturers recommended rate and applied during crop flowering within 2-3 days of inoculum arriving at the ear (this presentation was cut tragically short due to a lack of blood to the brain1). The third presentation on fungicides was given by Gary Van Ee (Michigan State University, USA) who showed how greater chemical deposition on the ear could be achieved using two flat fan nozzles one angled forward and the other backwards, especially when the nozzles were angle at 60‡ from the vertical. Ruth Dill- Macky (University of Minnesota, USA) and Wilfred Hermann (University of Hohenheim, Germany) both looked at how cultural practices could reduce levels of FHB. They highlighted that the principle factors to consider were previous crop (try not to grow wheat following maize), tillage (minimum or no till gave highest disease levels) and use of fertilisers/green manures to help increase residue decomposition.
The final two presentations in this session examined the role of biological control. Gary Bergstrom (Cornell University, USA) set the scene and was followed by Jeannie Gilbert (Agriculture and Agri-food Canada) who showed results from three projects which examined the usefulness of Cochliobolus sativus, Pseudomonas chloraphis, Bacillus amyloliquefaciens, B. subtilis and Trichoderma harzianum in the control of F. graminearum.
The fifth session was a short one dealing with food safety. Hans van Egmond started by detailing the worldwide regulations for fusarium mycotoxins as determined by a FAO investigation in 2003. Jim Pestka then covered the known adverse health affects of trichothecene mycotoxins and Antonio Logrieco detailed the occurrence of beauvericin and enniatins within European cereals.
The sixth session covered pathogenesis, epidemiology and disease forecasting. This session had two presentations detailing the US and Canadian forecasting systems which aid fungicide spray decisions and predict mycotoxin contamination at harvest by Larry Madden and Art Schaafsma respectively. Naresh Magan presented results from in vitro and in vivo interaction studies which should how other grain mycoflora can affect the growth and mycotoxin production of Fusarium species. Other presentations covered ultrastructural studies of the infection process, the use of real-time PCR to study epidemiology and the use of mycotoxin-negative mutants to determine the role of mycotoxins as pathogenicity factors.
The seventh and final session detailed taxonomy, population genetics and genomics. This session almost solely covered Fusarium graminearum.
Overall the session indicated that with the aid of the genome sequence and microarrays there is an opportunity for a rapid advance in the understanding of this species complex.
Overall the 2nd International Symposium on Fusarium Head Blight was a great success. The venue, facilities and organisation were excellent.
The main benefit was the opportunity to meet researchers from the around the world, in particular the large contingent of US and Canadian scientists present. One unusual feature of this International Symposium was the attendance by a number of farmers. The discussions greatly benefited from their feedback as to what results were useful to them, what questions they needed answering and what anecdotal evidence they had which supported, or otherwise, the scientific evidence. Over 320 scientists, growers, and industry representatives from 27 different countries participated in this Symposium. It was the largest gathering to date of scientists and stakeholders working on combating this disease.
Finally, a date for your diaries. The next International Fusarium Head Blight Symposium is due to take place in Szeged, Hungary in August 2008, timed to link with the Torino ICPP congress.
Paul Nicholson John Innes Centre, Norwich Phil Jennings CSL, York Simon Edwards Harper Adams University College, Shropshire Arsalan Daudi Rothamsted Research, Harpenden
