Development of a PCR-based diagnostic technique for light leaf spot (Pyrenopeziza brassicae) incidence on winter oilseed rape (Brassica napus subsp. oleifera)

Light leaf spot, caused by the fungal pathogen Pyrenopeziza brassicae Sutton and Rawlinson (anamorph Cylindrosporium concentricum), is a major disease of winter oilseed rape (Brassica napus subsp. oleifera) in the UK, causing losses estimated at >£30 M per annum. Effective disease control can be achieved by fungicide applications in November/December when initial infection occurs. However, disease symptoms are often not visible until February/March and can be difficult to identify. In addition, epidemics have been found to vary in severity between seasons and between regions in the UK. Consequently, spray decisions are often taken without knowing if crops are affected by the disease. One of the components of a light leaf spot forecasting scheme currently under development [1] is the early detection of light leaf spot infections as this will enable more timely decisions to be made regarding the application of appropriate control measures. To achieve this, we are developing a molecular diagnostic technique for light leaf spot, based upon the polymerase chain reaction (PCR).