Biostimulant seed priming enhances germination, early field emergence and osmotic stress responses, accompanied by a distinct metabolic signature in Brassica napus L

Biostimulant-based seed priming in Brassica napus offers a sustainable approach to improve crop establishment and stress resilience. We compared an Ascophyllum nodosum biostimulant (EpiSeed) with hydropriming and untreated controls in spring and winter oilseed rape varieties. We integrated laboratory assays, mannitol induced osmotic stress germination test, a single site field trial, and GC-MS metabolomics across four stages: after priming (AP), dry seeds, 6h re-imbibition under non-stress (6h-NS), and osmotic stress (6h-DS). EpiSeed priming significantly accelerated germination, enhanced early root growth and improved mannitol induced osmotic stress tolerance during germination compared with hydropriming and controls. In the field, Lagonda variety spring oilseed rape seeds primed with EpiSeed showed significantly faster seedling emergence, a non-significant trend in yield increase (15%), and reduced seed glucosinolate content (9%) in a single growing season. Metabolomics of the same variety identified 26 differentially accumulated metabolites. During priming, both treatments enriched alanine, aspartate, glutamate, cyanoamino acid, arginine, proline, and branched-chain amino acid (BCAA) metabolism pathways. During re-imbibition, responses diverged: under non-stress, EpiSeed showed coordinated metabolic utilization consistent with rapid growth and seed-to-seedling transition, whereas hydropriming altered mainly 4-aminobutanoic acid (GABA). Under osmotic stress, EpiSeed was associated with a more growth-oriented metabolic response via arginine and proline metabolism, while hydropriming exhibited a survival-oriented strategy dominated by BCAA and alanine, aspartate, glutamate pathways. Temporal trajectory analysis revealed a persistent EpiSeed specific metabolic signature marked by 4-hydroxyproline, consistent with cell wall related metabolism and growth activation. Collectively, EpiSeed establishes a distinct metabolic signature linking early biochemical reprogramming to improved germination, osmotic stress resilience, and field performance in oilseed rape.