Strip-cropping legacy enhances potato plant defence responses to aphids via soil-mediated mechanisms

Intensive agriculture often comes at the expense of soil health. A shift towards practices that foster soil health will support yield and defences against pests and diseases. Growing crops in monoculture is the standard in modern agriculture, though strip-cropping, in which different crops are planted in strips, is a promising strategy in the transition towards sustainable agriculture. Increasing crop diversity is hypothesized to positively influence arbuscular mycorrhizal fungi (AMF), thereby enhancing soil health, but the mechanisms by which AMF-plant symbioses contribute to higher yields and reduced pest populations in strip-cropping systems remain unclear. We used a green-house experiment with potato plants to explore the soil legacy effects of mono-cropping versus strip-cropping systems, AMF inoculation and aphid infestation on AMF root colonization, the induction of plant defences (untargeted LCMS-based metabolomics), aphid population size and potato yield. We found that potato plants grown in strip-cropping soil had higher AMF colonization than plants grown in mono-cropping soil. Potato plants grown in strip-cropping soil also had higher shoot nitrogen content, increased solamargine levels, and reduced aphid populations. AMF root colonization was only enhanced by the addition of commercial AMF in mono-cropping soils. Potato plant metabolites were affected by strip-cropping soil, including jasmonic acid (JA) derivatives. Structural equation models revealed that strip-cropping soil directly reduced aphid populations and also had a negative direct effect on the JA precursor OPC-8, and hydroxyJA-glucosides, indicating complex effects of strip-cropping soils on JA-inducible plant defences. Indirect benefits of strip-cropping soil and AMF inoculation on tuber yield were mediated by their direct positive effects on plant nitrogen content. Our results emphasize the potential of strip-cropping to enhance AMF root colonization in the field. We show that soil legacy effects of strip-cropping alter the plant metabolome in ways that suppress of aphid populations. Strip-cropping legacy effects are the result of crop diversity, crop neighbour and edge effects resulting from crop management practices. While the mechanisms by which soil from strip-cropping supresses pest populations still need to be identified, our study underscores the potential for strip-cropping to enhance pest control and yield via soil mediated processes. Read the free Plain Language Summary for this article on the Journal blog.