Phyllo-Micro-Meso-Agro Meteorology: Plant physiology & bioaerosols
Résumé
Mixtures of wheat cultivars can reduce disease propagation of septoria tritici blotch (STB) in the field. Growing together cultivars with contrasting levels of disease resistance provides disease protection for the most susceptible cultivar. Mixtures are generally constituted with cultivars of similar straw height. However, a contrast in plant height could have an impact on spore dispersal. For example, simulation studies showed that leaves from tall plants located above a short cultivar provide shelter from raindrops for diseased leaves at the bottom of the canopy, thus limiting the production of splash droplets carrying spores. Though this « umbrella effect » has been identified using a modelling approach, little experimental data is available on STB epidemics in cultivar mixtures with contrasted plant height. The objective of our study was to assess disease propagation within two binary mixtures composed of a short susceptible cultivar (~ 80 cm) and a tall cultivar (~ 160 cm), either resistant or susceptible. Susceptible pure stands and mixtures were grown during two years in field plots. Disease severity and plant height were recorded at flowering stage. Disease severity in susceptible plants was lower in both mixtures, composed of either resistant or susceptible tall cultivar, from 30 to 70% less than in pure stand, considering all plant leaves. Disease reduction was enhanced in the mixture including a tall resistant cultivar. For example, no disease was observed during the first year on the top three leaves of susceptible plants within that mixture. Our work suggested that mixtures of cultivars with contrasted plant height present a potential for enhancing STB severity reduction, possibly through physical mechanisms related to rain-splash dispersal. More extensive experimentations would be necessary to fully assess the relative contribution of the mechanisms leading to disease modulation in such mixtures