Effects of wheat varietal resistance level and rainfall characteristics on splash dispersal of Septoria tritici blotch

Abstract : Septoria tritici blotch is an important splash-dispersed disease, causing high yield losses in Europe. Plant disease propagation results from spore dispersal and susceptibility of plant tissues. An experiment was performed in order to study differents aspects of the disease dispersal cycle. Three wheat varieties with contrasted resistance levels were grown in greenhouse conditions until flowering. Plant canopies of each variety received rains of two different raindrop diameter distributions generated by a rain simulator. A linear inoculum source consisting of an aqueous suspension of spores was placed in the middle of each canopy. Horizontal and vertical spore fluxes were measured using traps composed of microscope slides. Varietal resistance was assessed in parallel. After incubation, leaves sampled in canopies were collected and scanned. Spore traps slides were photographed using a microscope combined with a digital camera. Disease area measurement and automatic spore counting were achieved using an image analysis software. Both disease and spore fluxes decreased with the distance from the inoculum source and lower mean raindrop diameter. Disease levels depended on variety and leaf level. Vertical and horizontal gradients of spore fluxes and disease varied in function of rain type and variety. Combining all these results made it possible to disentangle components of splash-dispersed disease propagation for a single dispersal event.