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 × 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.

Abstract- (control), -3, -5, -7, -9, -11 and -13 bars were performed using polyethylene glycol-6000 (PEG-6000). A completely randomized design with three replications was used for this experiment. Germination percentage (GP), germination rate (GR), mean germination time (MGT), root length (RL) and shoot length (SL

Genetic variability is a prerequisite for any plant breeding program, and mutagenesis is a proven way of creating new variation within a crop germplasm. Novel genetic variability in rapeseed was induced by gamma rays, Ethyl Methane Sulphonate (EMS) and combined mutagen treatment, using various doses and concentrations. The objective was to evaluate and compare the obtained M 2 mutants for important quantitative traits in two contrasted environments. Data on phenological, morphological and agronomic parameters were recorded. A large variability was observed and mutagenic treatments had a significant effect on all traits studied. Compared to control plants, mutant genotypes derived from seeds treated with low EMS concentrations during moderate time were earlier and characterized by a higher number of pods per plant. For high concentration of EMS during long time and for combinations of physical and chemical mutagens, a significant decrease in plant height and stature was noticed, as compared to control. Besides, plants derived from gamma rays-treated seeds exhibited the highest 1000-seed weight. The novel induced variability may be integrated in rapeseed breeding program as a new germplasm with improved agronomic traits. Particularly, EMS1-7-stable mutant may be exploited to develop efficiently and quickly a new rapeseed cultivar with some desirable traits. The present study highlights once more the possibility to bring novel genetic diversity for rapeseed desirable traits improvement through mutation breeding. Keywords: rapeseed / quantitative traits / mutation breeding / EMS treatment / Gamma rays Résumé -Développement et évaluation de divers mutants prometteurs de colza (Brassica napus L.) obtenus par mutagénèse physique et chimique. La variabilité génétique est essentielle pour tout programme d'amélioration de plantes et la mutagénèse s'avère une technique incontestable d'induction de nouvelle variabilité génétique dans les germoplasmes des cultures. Chez le colza, une nouvelle variabilité génétique a été induite après traitement de semences par les rayons gamma, l'EMS et leur combinaison, en utilisant différentes doses et concentrations. L'objectif de cette étude est d'évaluer et comparer les mutants M 2 obtenus pour des caractères quantitatifs, dans deux environnements contrastés. Les paramètres étudiés sont d'ordre phénologique, morphologique et agronomique. Une grande variabilité a été observée et les traitements mutagènes ont eu un effet significatif sur tous les paramètres. Les mutants qui proviennent d'une faible concentration d'EMS, durant une période modérée, sont plus précoces et ont un nombre de siliques plus élevé que la variété témoin (non traitée). Par contre, des mutants dérivés de forte concentration d'EMS, pendant une longue période, et de la combinaison d'EMS avec les rayons gamma, ont montré une réduction significative de la hauteur et de la vigueur des plantes. Par ailleurs, les plantes dérivées de ☆ Contribution to the Topical Issue "Rapeseed / Colza"