Drought Effects on Seed Yield Stability and Oil Quality Traits in Different Rapeseed Genotypes: Toward Adaptive Sustainability of Crops in Semi-Arid Regions

Rapeseed (Brassica napus L.) is a major oilseed crop worldwide, particularly valued for its high yield potential, favorable fatty acid composition, and its bioactive compounds that improve nutritional and industrial quality. However, its productivity and oil quality are increasingly compromised by climate change-induced water scarcity, particularly in semi-arid Mediterranean regions. In this study, the performance of 17 genotypes was evaluated under well-watered (irrigated) and rainfed (stressful) conditions across two contrasting locations, Douyet Experimental Station (DYT) and Ecole Nationale d’Agriculture de Meknès (ENAM), during the 2023/2024 growing season. The assessment concerned seed yield, oil traits, and nutraceutical quality. The results obtained show that drought stress significantly reduced seed yield by about 26% (from 2.29 to 1.69 t ha−1) and decreased oil content by about 8.3% (from 41.1% to 37.7%). The highest reductions were observed for sensitive genotypes, particularly ‘IND23’, ‘IND82’, and ‘H2M-5’, while ‘Moufida’, ‘Nap9’, and ‘TP2’ maintained seed and oil yield above the overall average across both water regimes. Drought also impacted the accumulation of secondary metabolites, with mean total phenolic content increasing from 5.41 to 9.98 mg GAE g−1 (+84.5%) and total flavonoid content rising from 25.25 to 34.93 mg QE g−1 (+38.3%) under rainfed conditions, accompanied by marked increases in antioxidant activity (DPPH, ABTS), particularly for ‘Moufida’, ‘Nap9’, ‘TP2’, and ‘Marina’. Oil quality indices remained within Codex Alimentarius standards, with a slight increase in acidity values accompanied by a decrease in peroxide values, thus suggesting improved oxidative stability. Principal component analysis grouped genotypes into distinct clusters, with an elite group (‘Moufida’, ‘Nap9’, and ‘TP2’) characterized by yield stability, accumulation of phenolics, and high antioxidant activity, thus confirming their strong adaptation to the dry conditions of the Mediterranean region. These drought-tolerant lines, with high agronomic performance combined with good nutritional quality, can be recommended as valuable cultivars for sustainable and high-quality rapeseed production in dry Mediterranean regions.