Does canopy architecture play a role in the effect of plant density and sowing date on epidemics of Septoria tritici in wheat crops?

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Septoria tritici is one of the most damageable wheat foliar diseases in Europe. It has been suggested that sowing date and plant density influence its epidemics. The aim of this study is to better understand these effects and to evaluate the hypothesis that they result from changes in canopy architecture. Indeed, several field studies have pointed out that canopy architecture may influence S. tritici development. However because interactions between canopy structure and pathogen are numerous and change constantly during the growing season, field data analyses are complicated. To overcome these difficulties, the approach here combines modelling and experiments. In 2007 and 2008, field trials in three locations were set up in which sowing date and density were varied. Disease assessments on the upper leaves showed that these treatments resulted in a wide range of epidemic's levels. The effect of sowing date and density on epidemics varied with the year and the location with a strongest effect of the sowing date. Canopy architecture also showed variation in organs dimensions, phyllochron and tillering dynamics. We used Septo3D, a wheat architectural model coupled with a S. tritici model to simulate the time course of leaf area index and crop architecture in each treatment. We used these results to evaluate the hypothesis that change in canopy architecture is determinant for the change in epidemics between treatments. Our approach appears of interest for evaluating the role of crop architecture in epidemic development and could thus aid in identifying beneficial agricultural practice combinations