Using wheat cultivar mixtures as a control method against Septoria tritici blotch: Experimental and modeling approaches
Résumé
Septoria tritici blotch (STB), caused by Zymoseptoria tritici, is a worldwide wheat disease of concern that may lead to major yield-damaging epidemics. Because STB is rain-splash dispersed at short distances during the host growing season, cultivar mixtures are expected to provide a rather low efficiency in disease reduction. However, quantitative data are still lacking to specify what it actually is. We used both experimental and modeling approaches in order to figure out how mixing cultivars can decrease STB severity. From 2008 to 2012, field experiments were conducted on binary wheat mixtures, with a 1:3 moderately susceptible:moderately resistant ratio. The number of sporulating lesions, and the diseased and green leaf areas were assessed on a weekly basis. All the results showed consistent reductions of STB symptoms on the more susceptible cultivar (ca. 40% less diseased area over the five years), without significantly affecting the more resistant cultivar, comparatively to their respective pure stands. In parallel, a biophysical model was developed to extend our experimental findings. It relied on the combination of virtual 3D wheat-like canopies with heterogeneous host resistance levels, and mechanical description of trajectories of pathogen-bearing splash droplets. Using this modeling approach, we pointed out the necessity to consider the accurate cultivar resistance levels in order to find the optimal cultivar ratio, maximizing the mixture efficiency.