Rebecca K. Vandegeer, Ximena Cibils-Stewart, Richard Wuhrer, Susan E. Hartley, David T. Tissue, Scott N. Johnson
Farmers face many challenges in the management of their crops, including insect pests and drought that can both drastically reduce yields.
Pest management using chemical pesticides can be costly, environmentally damaging and overuse can lead to pesticide resistance. An alternative management option may be to harness naturally occurring plant-based defences, such as silicon, which plants absorb from the soil and embed into their leaves as tiny particles. These particles are similar to sand and help defend the plant against insect attack by making leaves tougher and more abrasive. It would be equivalent to adding a sprinkling of sand to your salad lunch. Greater amounts of silicon in leaves is known to reduce the feeding of chewing insects and subsequently reduce their ability to absorb nutrients and grow.
In addition, drought is forecast to increase under climate change and will have broad effects on the natural environment and food production. However, the impact of drought on crop pests and interactions with plant silicon uptake is not well understood.
For our study, we grew a pasture grass, tall fescue, in a hydroponics system. Half of the plants received liquid silicon and half did not. In addition, half of each silicon treatment group were exposed to drought and half were not. The drought treatment involved adding polyethylene glycol, which restricts water moving into the plant. We took different measurements of plant growth and function, including x-ray microscope images of the exact locations where silicon was deposited on the leaf surface. We also placed caterpillars (the cotton bollworm) on the plants and measured their growth.
Drought caused many changes to the plant, including reducing leaf water content, but did not affect caterpillar growth. In contrast, silicon greatly reduced caterpillar growth due to a greater density of silicon particles on the leaf surface.
This study shows that silicon has the potential to be an effective weapon in the farmer’s arsenal to fight against insect pests and may hold up as a defence even during drought years.