Development and Application of a qPCR-Based Method Coupled with Spore Trapping to Monitor Airborne Pathogens of Wheat Causing Stripe Rust, Powdery Mildew, and Fusarium Head Blight

Common wheat (Triticum aestivum L.) production in China is challenged by stripe (yellow) rust, powdery mildew, and Fusarium head blight (FHB). Airborne inoculum of these pathogens is the causative driver of disease epidemics. Thus, monitoring of airborne inoculum on such fungal diseases is expected to provide some reliable estimations of disease development, especially by targeting multiple diseases simultaneously. This paper reports the development of a new practical qPCR-based method coupled with spore trapping to quantify simultaneously airborne inoculum of Puccinia striiformis f. sp. tritici, Blumeria graminis f. sp. tritici, and Fusarium graminearum & Fusarium asiaticum and discusses its potential use in disease-risk warnings. The technique can detect DNA of Pst, Bgt, and Fg at quantities as low as 0.2 pg (i.e. representing 0.65 urediniospores, 1.18 conidia, and 10 macroconidia, respectively), and neither Triticum aestivum DNA nor DNA of other common wheat pathogens were amplified. A linear relationship was produced between the number of spores on tape determined by qPCR and conventional microscopy, with a small variation (R2 value 0.97 to 0.99 depending on pathogen species). The daily concentrations of spores of the three pathogens were monitored using a Burkard 7-day recording spore trap, and the airborne spores were collected from a field near Langfang City, Hebei Province, China. The patterns of spore concentration dynamics in the air determined by triplex qPCR were close to those counted by conventional microscopy in a duplicated sub-sample. The developed assay can be an alternative to conventional microscopy to process large samples. This will improve monitoring power by providing timely risk warning information to growers regarding the timing of fungicide
applications.