Unveiling differential genotypic responses to soil moisture stress during early plant stages in rapeseed (Brassica napus L.)

In the context of climate change, rapeseed ( Brassica napus L.) is increasingly impacted by drought during germination and early seedling growth. Therefore, breeding for tolerance to such conditions has become a major goal for improving the resilience of this crop. This study investigates the responses of 12 rapeseed genotypes to low soil moisture during germination and seedling establishment. Four soil moisture levels, corresponding to 100 %, 70 %, 50 %, and 30 % of field capacity, were used, and various germination and early seedling growth traits were investigated, using univariate and multivariate statistical analyses. A pot experiment was conducted under controlled greenhouse conditions, using a completely randomized design with three replications. ANOVA results showed that most traits were significantly affected by drought stress. Drought conditions, particularly at 30 % FC, drastically affected all investigated traits, while significant differences were observed among the genotypes, suggesting different genetic potential in their reaction to early drought. Based on multivariate analyses, three distinct genotype groups were identified. Interestingly, group I comprises the most drought-tolerant genotypes, namely ‘Baraka’, ‘Nap10’, ‘Redana’, and ‘Nap9’, which demonstrated high potential for direct cultivation in arid regions and as promising germplasm in rapeseed breeding programs. However, the tolerance of these genotypes to late drought occurring at the flowering and seed-filling stages requires further investigation. Traits such as germination percentage, rapidity of germination, root system development, and shoot growth could be used as relevant selection criteria or indices for improving rapeseed drought tolerance in early plant growth stages. Given that most studies on rapeseed response to early drought have been conducted in-vitro , this work adds to the very few studies conducted in greenhouses in pots under more realistic conditions. It also offers four new, highly tolerant varieties that could be used as relevant germplasm in various breeding programs worldwide. • 12 rapeseed genotypes respond differently to soil moisture stress during early growth. • Baraka, Nap10, Redana, and Nap9 show the highest tolerance under early drought stress. • Germination performance and seedling growth are indices of early drought tolerance.