'Smart' cereals for management of stemborer pests in staple cereals in Africa

Stemborers are devastating insect pests of important food crops, maize and sorghum, in sub-Saharan Africa. They damage these crops by burrowing inside the stem causing the plants to collapse and die. Stemborer pests undermine smallholder cereal cultivation and threaten food security of the very high crop losses they cause. In previous research, we demonstrated that these losses can be prevented by changing the plant odours surrounding the crop. We used companion plants to release smells that repel the pest and attract natural enemy insects that attack the pest. The companion cropping system known as "push-pull" or "Sukuma-Vuta" in Swahili is very popular with smallholder farmers but this would be improved if the crop itself could release the appropriate odours when infested with pest insects. Recently we have found that certain farmer selected varieties of maize have a valuable defence trait not present in commercial hybrid maize. The trait involves release of odours, called semiochemicals, which are attractive to natural enemies of the pest after the stemborer lays her eggs on the plant. The semiochemicals released are the same ones released by companion plants in the push-pull system. The crop varieties with this trait, however, are lacking in other important agronomic traits, particularly yield and quality. To deliver this natural pest resistance to the farmer, breeding programmes are needed to move the trait from into improved crop varieties. This is a difficult process but would be greatly facilitated if genetic markers linked closely to the stemborer resistance trait could be identified. The goal of this project is to define genetic markers associated with the semiochemical production trait. We will achieve this by a comprehensive programme of experiments in which the semiochemicals emitted by different crop varieties after insect egg laying will be identified, insect responses to them measured and the underpinning genes associated with induced semiochemical emission mapped. We will use a state-of-the-art semiochemical identification platform available at Rothamsted Research (UK) and resources for genetic analyses at the Biosciences Eastern and Central Africa hub (BECA, Kenya) with a link to the Cornell University sequencing facility. Crops will be grown and trialled at the International Centre for Insect Physiology and Ecology (icipe, Kenya) which has a proven track record of doing research that is relevant to the needs of smallholder farmers in Africa and makes a difference to their livelihoods.

Stemborers are devastating pests of staple cereals in sub-Saharan Africa that reduce yields by up to 80%. Recently we have discovered that certain landraces of maize have an inducible indirect defence trait, not present in commercial hybrids, that involves release of semiochemicals attractive to natural enemies of the stemborer after eggs are laid on the plant. The same semiochemicals are released by companion plants in the push-pull companion cropping system. If this novel defence trait could be bred into cereal cultivars with other favourable agronomic characteristics, crop losses could be saved without having to grow companion plants to release semiochemicals. This project will develop molecular markers for the defence trait that will allow breeders to introgress it into improved lines of maize and sorghum. The project will start by growing many different lines of maize and sorghum from which headspace samples of volatiles will be collected and samples of DNA taken. Volatile profiles will be compared between plants with and without stemborer pest eggs and semiochemicals identified by GC-MS and GC linked to electrophysiology. Lines that show induction of semiochemicals after stemborer oviposition will be tested in bioassays with stemborer parasitoids (key natural enemies) and will be grown in field plot trials to assess stemborer infestation levels. Genotyping by sequencing and subsequent association mapping will be used to map the trait to the genes responsible. SSR and SNP molecular markers associated with semiochemical emission will be defined and used to screen germplasm. Gene sequences encoding synthases for the semiochemicals will be searched using bioinformatics. We also expect to identify genes involved in regulating the expression levels of the synthase genes following stemborer oviposition. We will also use bioinformatics approaches to search for orthologous genes associated with the trait between maize and sorghum genomes.

The project will have a clear role in increasing and sustaining yields of staple cereals in sub-Saharan Africa. According to the IMF poverty reduction strategy reports, growth in the agricultural sector in SSA countries is essential to reduce poverty and ensure food security; this will benefit mainly poor cereal-livestock smallholders (about 80% of producers). Agricultural growth is achievable by reducing major constraints to productivity such as insect pests. These constraints, already cause high levels of food insecurity, malnutrition and poverty, and are responsible for SSA cereal crop productivity being the lowest in the world (around 1t/ha compared with 2.4t/ha in South Asia, 3.2t/ha in Latin America and 4.5t/ha in East Asia and Pacific). They are expected to increase during the next few decades as agriculture intensifies to meet the extra food demand from a growing population and as a result of climate change.

Scientific impact will be made in terms of publications in good journals and all three partners have a good track record in this. We also have considerable experience in translation of our scientific research into farmer practice from the Push-pull project (push-pull is now used by more than 40,000 smallholders). This project will create strong linkages and collaborations among stakeholders - farmers, plant breeders and seed suppliers - at an early stage as a key condition for efficient technology adaptation and its wider dissemination to smallholder farmers in the target areas later in the project (e.g. please see letter of support from Western seeds). We will use farmer-to-farmer technology dissemination methods because they are cost-effectiveness in reaching large numbers of farmers. This is particularly relevant where public extension is either insufficient or ineffective as is the case in SSA, and serves a shared information and learning function of achieving economies of scale in technology diffusion and system financial sustainability. Here, farmers are expected to influence fellow farmers to adopt new technologies and practices. We will optimize the use of field days, farmer teachers and farmer field schools, in which we shall train farmers through the participating NARIs and NGOs, and provide them with both technology information and technical backstopping. The project will also produce and distribute dissemination brochures, some of which will be translated into local languages, by NARIs and other stakeholders. Additionally, stakeholder workshops, meetings and farmer exchange visits will be organized and more farmers exposed to the technology. The overall aim of these activities is to create nuclei of farmers adopting the technology to allow a horizontal transfer and uptake of the technology in the target areas. In all cases, adoption of a technology within a community can start off with a few individuals. Indeed, experience from the current push-pull project shows that small groups of individuals in a community pioneering adoption of a technology constitute very effective nuclei for its horizontal transmission.