Evaluation of rapeseed (Brassica napus L.) genotypes for tolerance to PEG (polyethylene glycol) induced drought at germination and early seedling growth

Rapeseed (Brassica napus L.) is an important oilseed crop well adapted to Mediterranean area. However, increasing drought, due to climate change, impairs its growth and development, mainly when this stress occurs early during germination. This study carried out in vitro conditions aimed to investigate the effect of water deficit on seed germination and seedling growth traits in 12 genotypes to select the most drought-tolerant ones. Drought conditions were created using polyethylene glycol 6000 to induce three osmotic potential levels, namely −0.7 MPa for moderate stress, −0.9 MPa for intermediate stress, and −1.1 MPa for severe stress. Germination percentage (GP), germination rate (GR), mean germination time (MGT), root length (RL), shoot length (SL), root-to-shoot ratio (RSR), seedling vigor index (SVI), shoot elongation rate (SER), and root elongation rate (RER) were measured/calculated. ANOVA and PCA were performed to analyze the data gathered. Results showed a significant effect of genotype, drought, and drought × genotype interaction on all studied parameters. Under severe drought conditions, overall values of GP, GR, RL, SL, SER, RER, and SVI decreased by 87.15 %, 53.29 %, 9.33 %, 4.73 %, 78 %, 82 %, and 96 %, respectively, while those of MGT and RSR increased by 56 % and 76 %, respectively, when compared to unstressed conditions. However, the genotypes studied reacted differently to the three levels of water stress. Based on PCA results, RL, RER, and GP proved to be the most discriminating of drought-tolerant genotypes. Overall, higher drought tolerance was associated with higher values in RL, SL, and SVI. Accordingly, the variety ‘Nap10’ and, to a lesser extent, ‘Baraka’ and ‘Nap9’ exhibited higher drought tolerance than the rest of genotypes, which makes them potential cultivars for dry areas. However, further studies in real field conditions are needed to confirm their tolerance to drought occurring at germination as well as during other stages, mainly flowering.