Integrated phenotypic, physio-biochemical, and metabolomic dissection reveals defense mechanisms of Brassica napus against aphid infestation

Brassica napus , a vital global oilseed and vegetable crop, suffers severe yield losses due to aphid infestation. Current reliance on chemical pesticides raises ecological and resistance concerns, making the elucidation of host resistance mechanisms a priority for sustainable agriculture. This study employed an integrated physiological, biochemical and metabolomic approach to compare a highly resistant line (CF101) and a susceptible line (CF138) under aphid stress. Comprehensive phenotyping and physiology revealed that CF101 possesses superior and stable vegetative growth, enhanced photosynthetic performance, stronger basal antioxidant capacity, and more potent induced defense responses. Metabolomic profiling identified a coordinated defense network, with CF101 showing upregulation of key metabolites from the shikimate-phenylpropanoid pathway (e.g., phenolic acids, lignin precursors, coumarins), benzoxazinoids, oxylipins, and glucosinolate synthesis precursors. Concurrently, metabolites serving as potential aphid nutrients or involved in certain signaling pathways were downregulated. This profile suggests a dual strategy of enhancing direct chemical defenses while limiting resources available to the pest. Functional validation confirmed that exogenous application of two identified metabolites, L-Malic acid and 3-Aminosalicylic acid, significantly enhanced aphid resistance through antibiosis and repellency, though at a cost to vegetative growth. Our findings provide novel, systemic insights into the physiological and biochemical foundations of aphid resistance in B. napus , revealing specific metabolic pathways and candidate compounds that can inform future breeding programs and integrated pest management strategies.