Abstract
Drought stress and salt stress are serious challenges to crop productivity in the arid lands. This work investigates the impact of NaCl-salt stress and PEG-water stress on germination and embryo growth of two sesame cultivars. The red seeds of Sohg were larger with oblong appearance and lower density relative to the white seeds of Shnd. Seeds were germinated in the dark in isosmotic solutions of NaCl and PEG-6000 at 0, -0.103, -0.205, -0.410 and − 0.615 MPa. The time-based parameters, e.g. velocity, uniformity and synchrony of germination were more reliable measures of germination efficiency than the final germination percentage. The impact of PEG was more severe than that of NaCl particularly on Sohg. The peaks of daily germination percentage were lowered and delayed under stress. The genotypic variability in germinability became evident under stress in favor of Shnd. Radicle length was the most reliable measure of seedling growth but was subjected to stronger impact of NaCl than PEG. Although Na+ mobilization from the seed to the emerging embryo was indifferent in the two cultivars in PEG solutions, Shnd exhibited higher Na+ uptake from NaCl solutions. Whereas K+ mobilization was restricted by NaCl only in Sohg, it was hastened by PEG equally in the two cultivars. The stress-vulnerable cv. (Sohg) recovered with higher magnitude than Shnd, particularly from the more stressing osmoticum (PEG). The indices of germination recovery were highest in PEG-pretreated Sohg while the fresh weight of recovered seedlings was highest in NaCl-pretreated Sohg.