Sustainable approaches to crop protection: silicon supplementation and its effects on symbiont-mediated multitrophic interactions

Outbreaks of insect pests damage crops and are predicted to increase under climate change. Controlling them with synthetic pesticides is environmentally damaging and sustainable alternatives are urgently needed. Supplementing soils with silicon (Si) offers such an approach: in cereals, Si increases crop yield and resistance to pests. It is not known whether Si benefits other important crop families such as legumes, nor whether there are indirect effects of Si supplementation on other species associated with herbivores, such as symbiotic microbes. Symbiotic microbes can substantially affect the performance of herbivores and thus the productivity of the crop, so understanding these interactions is important for future food security.

This project will investigate the effect of Si supplementation on the interactions between plants, insects and microorganisms. We will study lucerne, also known as alfalfa, an important forage crop globally as a model legume, its major pest the pea aphid, and the aphid’s symbionts. Si addition to legumes can increase the number of nodules containing nitrogen-fixing Rhizobia, and hence increase aphid performance, but this has only been shown once – we do not know the generality of this effect, nor do we understand the underpinning mechanisms. Obligate bacterial symbionts living inside specialised cells of the aphid are likely to modulate any nutritional effects of Si on the aphid, whereas facultative symbionts could influence the indirect effects of Si on natural enemies of the aphid.

This project aims to gain a mechanistic understanding of these multitrophic interactions so we can understand when and how Si supplementation provides a net benefit to the crop and can be a sustainable alternative to synthetic pesticides. To address this, the student will receive training in entomological, molecular and biochemical methods to measure aphid and symbiont performance, plant nutrients and the deposition of Si defences.