Assessment of safflower genotypes for individual and combined effects of drought and salinity stress at early seedling growth stages

Safflower is a highly valued oilseed crop. Safflower oil is a source of monounsaturated and polyunsaturated fatty acids which are important for a plurality of industries including the edible vegetable oil industry. Safflower is highly resistant to salinity and drought stress, which impede seed germination. Two safflower cultivars and 4 lines were screened against nine levels of osmotic stress treatments (using NaCl0 and PEG 6000(0) (control), NaCl-0.2, NaCl-0.4, PEG 6000(-0.2), PEG 6000(-0.4), PEG 6000(-0.2)+NaCl-0.2, PEG 6000(-0.2)+NaCl-0.4, PEG 6000(-0.4)+NaCl-0.2, PEG 6000(-0.4)+NaCl-0.4 MPa) for 8 days at seed germination stage. The osmotic stress was observed to induce a negative effect on the percentage of seed germination, shoot length, root length, root/shoot length ratio, fresh and dry weights of seedlings as well as on germination, and seedling vigor index. Lines and varieties significantly differed for respective and combined effects of stress treatments at early seedling growth stages. These results demonstrated that the respective effects of PEG 6000 and NaCl on safflower genotypes seedlings were less detrimental than the combined effects. Despite safflower varieties and lines were observed to be affected differently by individual and combined stresses, cv. Dincer, lines G-8, and G-6 showed a tolerance response to the studied conditions. Significant positive correlations were identified between shoot length and germination percentage (r = 0.91*), and root length (r = 0.98**). A significant correlation was observed between seedling dry weight and root length (r = 0.94**), shoot length (r = 0.91*), and seedling fresh weight (r = 0.97**). Similarly, significant correlation coefficients were noted between seedling fresh weight and root length (r = 0.90*), and shoot length (r = 0.87*). Cv. Dincer, lines G-8, and G-6 were determined to be significantly tolerant against salinity, drought, and combined stresses for the studied traits using principal component analysis. According to these findings, effects individually produced by salinity and drought on seedlings of safflower are less damaging to plant development when compared to the combined effects of said two stresses. This study emphasized the importance of monitoring the genotypes of safflower for salt and drought stress tolerances in breeding programs.