Quantification of the architectural effects of wheat canopies on the interception of splash dispersed spores
Résumé
Crop canopy architecture affects the dispersal of airborne fungal spores of plant diseases, in particular in the case of septoria tritici blotch (STB) which is an important wheat disease mainly spread by rain splash. Therefore, the characteristics of canopy architecture (medium of dispersal of the pathogenic agent) can be taken into account to implement alternative disease control methods in order to slow down the vertical dispersal of STB in the field. And for the particular case of cultivar mixtures, different plant architectural traits can be used to improve the “barrier” effect on spore dispersal, which is provided by the most resistant components in the mixtures (see Vidal et al. in this issue). We investigated, by the mean of experiments under controlled conditions and modelling, the effects of the canopy architecture on one dispersal cycle of spores of Zymoseptoria tritici. The experiment was performed using a simulator of artificial rains on micro-canopies of wheat (1 m2), which were grown in a controlled greenhouse environment. A linear inoculum source of spores suspension was exposed to a simulated and calibrated rainfall event in order to get reproducible splash-dispersal towards four types of canopy differing by their architectures characterized by their leaf area densities (LAD). Splash droplets of the suspension were collected at different locations within the canopies to quantify spore fluxes and the resulting disease severity and incidence were assessed after the latency period. Based on a mechanistic modelling of spore dispersal and a 3D numerical reconstruction of the canopies, we quantified strong effects of the canopy structure on the spore dispersal. Denser canopies (i.e. with higher LAD) had a higher rate of spore interception that led, (i) for susceptible cultivars, to a higher disease severity, and (ii) for the resistant cultivars, to a higher spore trapping rate and therefore to a better “barrier” effect in the case of cultivar mixtures.