Detection and quantification of airborne inoculum of Pyrenopeziza brassicae in Polish and UK winter oilseed rape crops by real-time PCR assays.

Following a sudden outbreak of light leaf spot disease in Polish winter oilseed rape crops at the beginning of the last decade, volumetric spore traps installed around the country were used for the detection of ascospores, which constitute the primary inoculum of Pyrenopeziza brassicae, the causal organism. In 2004–2008, weather conditions that were adverse to the development of the pathogen appeared to have hindered the macroscopic signs of light leaf spot disease symptoms on oilseed rape, even in Pomerania, a region in north Poland, which cultivates the crop intensively and is favourable for the disease. Recently, however, the development of β-tubulin-based primers and dual labelled fluorescent probes has enabled the detection of minute quantities of P. brassicae DNA that correlated highly and positively with low abundance of inoculum of the pathogen in air samples. Depending on the season, the Spearman's correlation rank between spore abundance obtained by light microscopy and P. brassicae DNA yield determined by quantitative polymerase chain reaction (qPCR) on extracts from spore sampler tapes varied from 0.256 to 0.562. These primers and probe also detected P. brassicae in DNA extracted from tapes of spore traps operated in the autumn of 2006 and 2007 within field sown winter oilseed rape crops in Harpenden, southern UK. [ABSTRACT FROM AUTHOR]