NaCl salt stress and PEG water stress differentially affect germination and early seedling growth of two sesame (Sesamum indicum L.) cultivars

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 (Sesamum indicum L.) cultivars: Sohag 1 (Sohg) and Shandaweel 3 (Shnd). Seed dimensions, volume and weight were measured. The red Sohg seeds were larger with oblong appearance and lower density relative to the white Shnd seeds. Seeds were germinated in isosmotic solutions of NaCl and PEG-6000 at 0, - 0.103, - 0.205, - 0.410 and - 0.615 MPa. The time-based parameters (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 peak of daily germination was lowered and delayed under stress. The genotypic variability in germinability became evident under stress in favor of Shnd. Radicle length-a reliable measure of seedling growth-was subjected to stronger impact of NaCl than PEG. Although Na+ mobilization from seeds to embryos was indifferent in the two cultivars in PEG solutions, Shnd seedlings 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 Sohg recovered from stress with higher magnitude than did Shnd, particularly from the more stressing osmoticum (PEG). The indices of germination recovery were highest in PEG-pretreated Sohg while the biomass of recovered seedlings was highest in NaCl-pretreated Sohg.