It’s hard to see maize, a popular cereal in agriculture, as a particularly malevolent force of war, but as it happens these ingenious crops are all about strategy when it comes to battle. Plagued by stemborers, a type of crop parasitism, maize can launch a chemical defense that essentially calls in the cavalry in the form of the parasite’s natural enemies: wasps. In a new study published in the journal Scientific Reports, scientists have isolated the genetic markers that make this remarkable alarm system possible. It’s hoped that the discovery will aid farmers across the world in protecting their crops from parasite infestations that can destroy livelihoods.
Stemborers are devastating pests of cereal crops in sub-Saharan Africa, ruining their commercial value to the farmers who depend on them. Tritrophic interactions allow plants such as the popular crop maize to launch a counterattack on invading parasites by summoning their sworn enemies. Some maize plants launch this effective counterattack during the early stages of a stemborer infestation as the moth lays eggs on the crop. They release a chemical signal that summons parasitic wasps who kill the stemborers by parasitizing them.
This defense isn’t present in all maize variants however, and the researchers wanted to uncover the genetics that underpin this favorable trait for commercial crops. They investigated the genetic variability of 146 maize genotypes looking at landraces (varieties selected for by local farmers) and commercial hybrids. They also used samples of the maize variants to see how effective they were at attracting the parasitic wasp Cotesia sesamiae.
Their results showed that the plants best at launching a defense against the egg-laying parasites were landraces rather than inbred lines. Genetic analysis also identified 101 markers associated with the “call for help” response, which they hope could one day be selected for by maize breeders to help protect their crops.
Genetic modification or GMO crops is often considered a controversial area of science, but for centuries agriculture has developed thanks to farmers actively selecting favorable crops for their desirable traits. The economic impact of poor pest control for farmers can be catastrophic, and so biological interventions such as selecting for maize’s incredible ability to “send in the wasps” could be an effective tool for protecting livelihoods. The development of such organic defenses could likely lessen the need for chemical pesticides that can cause nutrient run-off and algal blooms, devastating aquatic ecosystems.
“Farmers urgently need alternative approaches for managing crop pests as use of pesticides is increasingly restricted by changes in legislation and evolution of pesticide resistance,” said lead researcher Professor Toby Bruce from Keele University, UK, in a statement. “Here we show how biological control of pests can be enhanced in crops. We have identified regions of the maize genome associated with a ‘cry for help’ trait that allows crops to call in parasitic wasp bodyguards to defend them when they are attacked by pests.”