Canopy architecture is a driver to limit the development of fungal aerial diseases. The architectural variability of cultivated pea makes the pathosystem ascochyta blight-pea an excellent candidate for such a study. Here, we tested two sets of hypotheses to explain the disease progress from the bottom to the top of the canopy during the cropping season: i) the presence of a receptivity gradient of pea organs linked to their senescence level, and ii) the presence of a wetness gradient with longer leaf wetness duration (LWD) at the bottom of the canopies. Field trials involved three cultivars, differing by their architectural features and sown at different densities to generate contrasted architectural scenarios. Greater senescence and disease levels were obtained in the densest canopies, due to shading caused by the high leaf area indexes of the upper layers. Experiments under controlled conditions also showed that senescent organs were more susceptible to the disease. Moreover, LWDs, recorded at the bottom and mid-level of the canopies, were favourable for disease infection only during rainy periods, according to a model adapted from Magarey et al. During these periods, LWDs were longer inside the canopy than above it. Our results thus show that canopy architecture impacts epidemic development both directly and indirectly, but cannot provide alone a full disease escape. It can thus usefully be combined with other disease management methods such as genetic resistance.
