Could Canola Canopy Architecture Affect Pathogen Infection by Impacting Flower Accumulation on Branches?

Sclerotinia sclerotiorum, a fungal pathogen of canola (Brassica napus), can cause yield losses exceeding 20%. An important route for disease is through infected flowers falling and accumulating on branches, which act as a source of inoculum to infect the stems, resulting in stem rot, wilting, plant collapse, and, ultimately, yield loss. The branching architecture of canola may affect Sclerotinia infection by affecting flower accumulation in canopies; however, our understanding of this effect is limited. This study explored how changing canola canopy architecture affected Sclerotinia infection rates via flower fall within a simulated field setting. To investigate this, we created a new static structural model coupled with a novel model of flower fall that accounts for wind conditions. Upright architectures resulted in increased infection by positioning more flowers above axils, which increased flower accumulation on branches, whereas outstretched branching reduced infection by positioning fewer flowers above axils. However, no single architecture consistently resulted in the lowest infection rate across a range of wind conditions. The coupled functional-structural model helped dissect the effects of wind, crop plant architecture, number of infected flowers, and planting density on fungal infection in canola fields. This research suggests that manipulating plant architecture through lowering planting density or breeding could offer a simple and cost-effective strategy to help reduce Sclerotinia infection in canola fields. The results may have broader application to other crops for which infected flowers can act as a source of inoculum for stem disease.