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Towards a sustainable whole-farm approach to the control of ergot - LK0962

Description
Concern has been mounting in recent years about the increasing problem of ergot contamination in wheat. This has resulted in greater numbers of grain loads being rejected for milling and in seed failing to reach the certification standards.

Recent changes in farming systems have been implicated, in particular the introduction of grass margins in arable fields, encouraged by CAP reform. The risk is that flowering grasses in the margins will become infected by ergot and act as a source of inoculum for the adjacent wheat crop as well as adding to the reservoir of ergots available to initiate the next season’s infection cycle. Other trends contributing to the increased ergot problem may include poor control of grass weeds because of increased herbicide resistance, shorter rotations, and earlier sowing.

The aim of this project is to develop an integrated package of measures aimed at reducing the risk of ergot infection in wheat crops whilst retaining the environmental benefits of grass margins. The importance of grass field margins as a source of ergot inoculum will be assessed and means of reducing this risk will be explored. These will include low risk’ grass species that are unlikely to act as a source of infection for wheat and margin management regimes that reduce the risk of ergot infection spreading to the crop. The resistance of wheat varieties to ergot will be investigated in order to identify low risk varieties with flowering characteristics that confer escape from infection or with resistance that is effective at a later stage once infection has occurred.

The research will combine monitoring of farm and experimental field margins, artificially inoculated and naturally infected field and glasshouse experiments, spore trapping and epidemiological studies and will use quantitative PCR diagnostics for pathogen detection.
Objective
Objective(s)
11.1 Scientific objective(s)
1. Establish the ergot status of representative country stewardship field margins in relation to their grass species composition and management
2. Determine whether populations of Claviceps purpurea supported by different margin grass species differ consistently in their pathogenicity for wheat
3. Determine the extent to which field margins contribute to ergot infection in cereal crops (using wheat as a model).
4. Quantify spatial distributions of C. purpurea resulting from primary spread (ascospores) and secondary spread (condia).
5. Examine variation in ‘field resistance’ to ergot amongst current UK wheat varieties. Determine the degree to which this is attributable to ‘escape’ (as conferred by flowering biology) or to post infection resistance.
6. Develop a PCR diagnostic for quantitative detection of C. purpurea.

11.2 Interdependence of objectives
A quantitative PCR diagnostic (Objective 6) is an essential tool for achievement of Objective 4 and will also lead to greater efficiency in studies addressing objectives 1 and 3.
Ergot samples collected in monitoring studies addressing Objective 1 will be cultured and form the basis of experiments addressing Objective 2.
Wheat-pathogenic isolates identified in Objective 2 will be used for inoculated tests of wheat variety resistance (Objective 5).

11.3 Chances of achieving objectives
Objectives 1 (and 3): there is a high chance of achieving these objectives because the project consortium has widespread access to contrasting margins in farm and experimental situations, made available through industrial and science partners and project consultants. This includes the BUZZ and SAFFIE projects and organic farming research sites (via links with Elm Farm Research Association).
Objective 2: Various procedures are available for inoculating wheat with ergot strains to determine pathogenicity, and consortium members have recent and sucessful experience of using some of the techniques in different research programmes. While there will be a need to optimise a technique which will allow for a large number of strains to be tested and give sufficiently reproducible distinction between them, this work will be applying the principles of previously published methods and has a very high chance of succeeding. Manipulation of the inoculation environment via mist irrigation will also help to provide a high degree of certainty for this part of the work.
Objective 4 (and 3): Although there is a great variability in both timing and location of ascospore release on farms, the proposed research will test numerous locations at several sites over two seasons and with a high level of replication (of passive traps) at each location. Therefore the risk of not recording any meaningful data will be reduced, allowing the key question of the relative importance of margins as sources of ergot inoculum, compared to other farm environments, to be assessed.
The controlled field experiment studying the dispersal of inoculum from artificially infected margins further enhances the chances of objective 4 being achieved. In these experiments the chances of ergot germination and ascospore release will be maximised, maximising the chances of producing reliable data on the effectiveness of margins as sources of inoculum.
The proposed study of primary infection gradients uses controlled experiments, which simulate natural conditions but ensure a high probability of recording useful data by (i) deliberate seeding of different amounts of ergot inoculum at known (marked) points (to study primary ascospore inoculum) (ii) a back-up of ergots sown in pots of soil and vernalized in case of lack of visible ascomata production from ‘sown’ ergots. (iii) the ability to water the inoculated area in the event of exceptionally dry weather, (iv) the period of spore trapping covering three months during the peak time expected for spore release, and (v) the trial being conducted over two seasons. In the study of secondary infection gradients, the inoculation procedure of the central blackgrass, at the onset of flowering or (later) wheat, at the onset of flowering, will be done in the evening (high humidity) and will be repeated at least twice over succeeding days. The risk of not establishing initial infection is therefore reduced considerably. Although conditions for secondary infections depend potentially on wet weather (for rain-splash but not insect spread), only natural conditions will be studied as artificial irrigation may not recreate the correct type of rain-splash. However the trial will cover two different growing seasons. As with objective 4 (above) useful data on spore distributions will be backed-up by ear infection assessments before harvest.
Objective 5: There is a high chance of achieving this objective because techniques for the artificial inoculation of cereals with C.purpurea are available and consortium members have experience of relevant methodology.
Objective 6: There is a high chance of achieving this objective as a DNA marker has previously been cloned and found to be specific for C. purpurea. The origin of this marker would suggest that it will not occur in other pathogenic or saprophytic fungi commonly found on UK cereal crops or grasses. Methods for the extraction and quantification of fungal DNA from spore-traps and plant material have previously developed by consortium members.

11.4 Factors, specific to the project, which might delay achieving the objective(s)
The main factors that might delay the achievement of the objectives are adverse weather conditions and delay in the development of a quantitative PCR
Ergot activity is sensitive to weather conditions when cereals and grasses are flowering. Very dry conditions in spring could occur in some areas and restrict the amount of crop infection. Adverse weather factors may limit the production of natural inoculum and infection needed for all naturally infected farm based studies. This would be compensated for in part by the controlled field experiments where inoculum production can be manipulated to some extent by misting.
Delay in producing a PCR assay would affect work on inoculum detection and disease assessment. Conventional methods of spore detection would allow work to proceed, by much less efficiently. Similarly conventional disease assessment methods could be used, but again they would be less efficient.
Time-Scale and Cost
From: 2004

To: 2008

Cost: £273,389
Contractor / Funded Organisations
National Institute of Agricultural Botany
Keywords
Agri-Environment              
Arable Farming              
Climate and Weather              
Climate Change              
Crops              
Farming              
LINK Programme              
Natural Resource Use              
Organic              
Sustainable Farming and Food              
Sustainable Production              
Fields of Study
Arable Crops