Unveiling drought-tolerant genotypes and associated adaptive mechanisms in rapeseed using multi-traits approach.

Rapeseed (Brassica napus L.) is a valuable oilseed crop due to its high nutritional value and rich oil content, making it a major source of edible oil. However, frequent drought events, aggravated by climate change, pose challenges to its productivity. Whereas a set of genotypes was previously investigated for their response to early drought during germination and seedling stages, the present study aimed to identify those genotypes exhibiting their tolerance to late-stage drought (occurring at flowering and maturity), and to elucidate their adaptive mechanisms, via an integrative multi-trait approach. A pot experiment was conducted under controlled greenhouse conditions, using a completely randomized design with three replications. The genotypes were evaluated for agromorphological, physiological, and biochemical parameters under two irrigation regimes (100% and 50% field capacity). Drought stress significantly reduced growth, yield components, and chlorophyll content. In contrast, water deficit induced accumulation of H₂O₂, MDA, relative electrical conductivity (EL), proline, and soluble sugars by about 40% and increased superoxide dismutase (SOD) and catalase activities by more than 42%. Nevertheless, the genotypes reacted differently to stress. Compared to the other genotypes, the varieties 'Nap9', 'Marina', 'Moufida', 'Baraka', and 'Redana' exhibited higher SPAD and Fv/Fm levels, along with lower concentrations of H₂O₂, MDA, and EL, indicating better drought tolerance. This tolerance was associated with increased enzyme activity and greater osmolyte accumulation. Drought reduced seed yield by 40% and increased H₂O₂ and MDA concentrations by 71% on average, whereas 'Nap9', 'Marina', and 'Redana' limited the increase in EL to only 20% while maintaining 12-14 g plant⁻¹ seed yield under stress. In particular, 'Nap9', 'Marina', and 'Redana' maintained better growth and higher productivity under drought, indicating their higher resilience. These genotypes could be a valuable germplasm for developing drought-tolerant rapeseed cultivars.