Push-pull companion cropping system soil legacies alter maize phytochemistry and resistance to insect herbivores

Plants can alter nutritional availability, structure and chemistry of the soil they grow in. These soil changes can positively or negatively influence growth and metabolism of other plants that co-occur or grow later in the conditioned soil. Plant-soil feedbacks could affect community interactions and dynamics but also be applied in sustainable agriculture to promote plant growth and resistance to pests. In this study we use a maize companion cropping system, commonly known as “push-pull”, as a model to investigate soil-mediated effects of functional biodiversity, on maize plant growth and resistance against insect herbivores. We grew maize in soils collected from push-pull (polyculture) and non-push-pull (monoculture) fields. We evaluated maize performance by measuring plant growth, and resistance traits (herbivore pest oviposition and larval feeding, production of defense-related volatile and non-volatile secondary defense metabolites). Maize plants grown in soil conditioned by push-pull had a higher growth rate compared to those grown in soil from non-push-pull fields. In addition, soil from push-pull fields induced a constitutively higher and qualitatively different emission of volatile organic compounds than soil from non-push-pull fields. Moreover, secondary defense metabolites including 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one, were produced in larger quantities in plants grown in soil from push-pull fields compared to those from monoculture fields. These soil-mediated alterations in plant secondary metabolism were associated with reduced herbivory by larvae of Chilo partelllus. This study provides novel evidence that plant-soil feedback can affect plant metabolism, growth and resistance to pests as well as additional mechanism of pest control in push-pull cropping system.