Quantitative PCR analysis of abundance of airborne propagules of Leptosphaeria species in air samples from different regions of Poland

When airborne propagules of Leptosphaeria maculans and L. biglobosa were collected in Poland at three ecologically different sites from 1 September to 30 November in 2004 to 2008, using a Hirst-type seven-day volumetric spore trap, there were fluctuations in timing of ascospore release and diverse ratios between airborne propagules of both species depending on season, field location and weather conditions. The detection was done using the microscope as well as quantitative PCR with species-specific primers targeted against fragments of β-tubulin genes and quantified with a dual-labelled fluorescent probe approach. This detection chemistry is described for the first time for L. maculans and L. biglobosa. Its advantage over the previous ITS-based SYBR-Green chemistry resides in improved sensitivity and the virtual absence of false positives in the detection of these fungi. There were significant, positive correlations between data obtained using visual assessment of ascospore numbers and DNA concentrations that were measured by qPCR. Climatic differences between the oilseed rape growing regions could have significantly affected the biological processes of pseudothecial maturation and ascospore development of the pathogens. The data suggest that regular rain events of intermediate intensity recorded in the Maritime region favoured the maturation of the pathogen more than the drier weather recorded in the Silesia or Pomerania regions. It was observed that the number of rainy days was of greater importance than the cumulative rainfall to obtain the generative sporulation of the pathogen. Accurate detection of airborne inoculum of pathogenic Leptosphaeria spp. facilitates improved targeting of disease management decisions for oilseed rape protection against phoma stem canker and stem necrosis diseases.