14CONFAP: Brazil-UK Partnership on Delivering Pest Resilience in Brazilian Smallholder Maize Crops

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Plants have evolved sophisticated defence strategies against biotic stress (pests) using a variety of inducible defence mechanisms that can be exploited in crop protection. Directly, they produce volatile small lipophilic molecules (SLMs) that are antagonistic to pests, and indirectly, they release SLMs as stress signals to attract pest natural enemies. Furthermore, neighbouring plants have evolved to respond to the stress signalling by induction or augmentation (priming) of their defence response. The ability to elicit or prime crop plants for defence upon detection of plant stress signalling provides an opportunity to develop new mixed cropping systems, whereby the identified stress signals associated with initial pest attack on sentinel (guard) crops can be used for the activation of defence in main crops. The overall aim of this project is to bring together UK and Brazilian partners to develop resilience in maize against fall armyworm, Spodoptera frugiperda, in smallholder farms in Brazil. This will be based upon the chemical ecology of maize/S. frugiperda interactions, for the deployment of a mixed cropping system that exploits plant/plant signalling from initially attacked plants for conservation (natural enemy) biocontrol in main crops. Different cultivars and landraces of maize will be evaluated to characterise the emission of S. frugiperda-induced stress signalling. Plants will be either unchallenged or challenged with S. frugiperda and headspace extracts containing the induced stress signals will be obtained by air entrainment. The stress signals will be analysed using GC-FID and identified using GC-MS. To confirm the biological activity of the identified stress signals, bioassays will be conducted to evaluate their influence on the foraging behaviour of pest natural enemies. To evaluate stress signal induction of defence in neighbouring maize cultivars and landraces, undamaged neighbouring maize plants (recipients) will be exposed to the stress signals released by S. frugiperda-damaged plants (donors). The induced signalling will then be collected from recipient plants and identified by GC-FID and GC-MS to see if the donor stress signalling has elicited a defence response in recipients. To confirm the biological activity of the stress signals released by recipients, bioassays will be conducted to evaluate their influence on the foraging behaviour of natural enemies. To evaluate differential expression of stress signal biosynthesis genes between stress-signal exposed and unexposed recipient plants, messenger RNA will be extracted from signal-exposed and unexposed recipient maize cultivars and landraces and subjected to Next Generation Sequencing transcriptome analysis. The differential expression of putative biosynthesis genes that specifically encode enzymes involved in stress signal biosynthesis will be confirmed using real time PCR analysis. These genes will be identified as targets for selection of maize cultivars and landraces with resilience to S. frugiperda, in which gene expression can be elicited by exposure to the stress signals identified. Field studies will be carried out on experimental-based plots at Embrapa Maize and Sorghum in Minas Gerais. Plots will be organised with mixed cropping of the maize cultivars and landraces that are shown to be either highly susceptible to fall armyworm damage and emit plant stress signalling (sentinel crops), or respond to stress signalling though elicitation of their own defence (main crops). After completion of the field experiment, farmers and extension officers known to Embrapa will be taken though Farmers Field Schools/Farmers Field Forum training where they will be educated on the mixed cropping strategy for maize protection. Once the mixed cropping system strategy for control of fall armyworm is developed and successfully demonstrated in farmer field schools/forums, it will be documented in simple language in factsheets and illustrated handbooks.