Push-pull cropping system soil legacies enhance glucosinolate production and subsequent defense against Diamondback moth (Plutella xylostella) larvae in Kale (Brassica oleracea)

Push-pull cropping integrates repellent ‘push’ plants with attractive ‘pull’ plants to manage insect pests and other ecosystem services. Whilst field evidence showed that push-pull cropping provides protection against diamondback moth (DBM) (Plutella xylostella), the mechanisms remain underexplored. This study investigated the influence of soil legacies formed under the push-pull system on kale (Brassica oleracea var. acephala) defense against DBM larvae. We compared responses of DBM larvae to kale grown in medium and old push-pull-conditioned soil to those grown in control soil using behavioural assays, larval performance tests, and glucosinolate profiling. Behavioural and feeding assays revealed a significant reduction in DBM larval survival (0–24%), feeding activity (leaf area eaten: 0.31–0.68 cm²), and orientation (28–32%) on kale grown in push-pull-conditioned soil. Phytochemical analyses indicated elevated concentrations of key glucosinolates, including gluconapin, glucoiberin, sinigrin, and glucobrassicin (0.01–1.08 ng sinigrin equivalents/g) from kale grown in push-pull-conditioned soil compared to those grown in control soil (0.1–0.87 ng sinigrin equivalents/g). Notably, glucocheirolin and glucotropaeolin were uniquely detected in kale planted in old push-pull-conditioned soil. These secondary metabolites are associated with defense against insect herbivory and potential dietary benefits to humans. Our study demonstrates that soil conditioned by push-pull can enhance the kale’s defense against pest herbivory through plant-soil feedback, paving the way for the sustainable production of kales.