Inter-seasonal and altitudinal inoculum dynamics for wheat stripe rust and powdery mildew epidemics in Gangu, Northwestern China

Inter-seasonal and altitudinal dynamics of airborne spores of wheat stripe rust and powdery mildew pathogens were studied in northwestern China (Gangu, Gansu) in this study. Burkard spore traps were placed in three locations of Gansu county of the Gansu province at various altitudes, named South mountain, Valley and North mountain. Airborne spore samples were collected from March 2013 to December 2015, totaling 1365 collections for each pathogen. The airborne spore concentration of both pathogen, quantified using duplex real-time PCR assay, were consistently higher in the spring and summer than in fall and winter seasons. The within-crop season airborne inoculum levels were associated with disease severity levels. No difference was found in the Area Under the Spore Concentration Progress Curve (AUSCPC) between spring and summer for both pathogens as well as among the three locations, and there was significant correlation of ten-day spore concentrations between any two of the three locations. Our findings suggest that Gangu is an important source of oversummering inoculum for both diseases with frequent exchange of airborne spores within this region. The time-series analysis demonstrated that the airborne spore concentrations of Pst for all the 10-day-spore-sum during 3 years at three locations were all significantly described by the Autoregressive Integrated Moving-Average (ARIMA) (1, 0, 0) models, while, those of Bgt fitted different models, which contributed to predicting the tendency of airborne spore concentrations for both pathogens in Gangu.