Reaction of some rapeseed (Brassica napus L.) genotypes to different drought stress levels during germination and seedling growth stages

Drought is a major abiotic stress that affects seed germination and plant growth in arid and semi-arid regions. Rapeseed is an oilseed crop adapted to Mediterranean area; however, it is reported that it is sensitive to water stress occurring during seed germination. In this study, we investigated how seed germination and early seedling growth of six rapeseed genotypes were influenced by different water stress levels. In addition to the control (absence of drought stress), three drought levels were simulated using three osmotic potentials of polyethylene glycol (PEG-6000), -9, 10 and 11 bars. A completely randomized design with three replications was used for this experiment. Germination percentage (GP), shoot length (SL), root length (RL), shoot elongation rate (SER) and root elongation rate (RER) were determined to evaluate the genotypes response to PEG-induced drought stress. Results showed drought stress, genotype and interaction stress x genotype had a significant effect on the studied parameters. GP decreased with the increase in stress level. The genotype 'Nap9' was the most interesting, having the highest GP values, namely 63.33, 62.67 and 28% under the stress levels -9, 10 and 11 bars, respectively. The genotype 'H2M-5', which ranked second with respect to this parameter, was statistically comparable to 'Nap9'. Also, SL, RL, SER and RER decreased with the increase in drought stress level. However, the studied genotypes reacted differently to various water stress levels. Once again, the genotype 'H2M-5' exhibited the highest average RL and RER under all drought levels. Particularly, for severe drought conditions (-11 bars), `H2M-5' had an average RL of 1.54 cm and RER of 0.36 cm/d. Field evaluation under controlled conditions is needed to confirm findings of the present experiment. The mutant 'H2M-5' could be a valuable and promising germplasm for developing a performant and adapted variety to be designed for harsh environments particularly characterized by early drought coinciding with germination and seedling growth stages.