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Pyrenopeziza brassicae


Contact: Dr David Kenyon
                Dr Jane Thomas

Light leaf spot of oilseed rape, caused by the fungus Pyrenopeziza brassicae, is a major disease of oilseed rape, causing losses estimated at £40 million per year. Variety resistance is a major breeding objective, and is evaluated as a major character for National List. Sustainable oilseed rape production for the future is heavily dependent on reduction of inputs to control diseases such as light leaf spot, but this relies on an accurate determination of disease resistance.

                       

Currently, this character is assessed by visual estimation of the extent of symptoms. This provides some indication of relative resistance, but in the case of light leaf spot, the situation is complicated by the existence of cryptic infections, where extensive colonisation of the leaf occurs, but sporulation (ie the visible symptom) is limited. Thus plants may be suffering a damaging infection, but this would not be recorded. Even when sporulation occurs, the symptoms of light leaf spot are difficult to see and quantify, requiring time consuming plot examination.

Quantitative PCR offers a rapid and potentially very accurate means of assessing the degree of fungal infection in a plant. Specific primer sequences for P brassicae have been identified, and published, and systems for extracting fungal DNA from plant material are available. Comparative variety resistance could thus be evaluated by PCR, and since this would take into account all infection, not just sporulating areas, a more accurate description of resistance could be achieved. Such a system is also likely to reduce the costs of testing, by avoiding lengthy plot examination, and replacing multiple field trials with a single inoculated experiment.

Project Objectives.
1. Establish a quantitative PCR test for DNA of Pyrenopeziza brassicae using published primer sequences.
2. Determine the relative resistance of oilseed rape varieties using PCR.
3. Devise approaches for implementing PCR as a routine system, which will deliver efficiencies in VCU testing

The financial support of DEFRA is gratefully acknowledged.