Effect of NaCl and PEG Induced Osmotic Potentials on Germination and Early Seedling Growth of Rice Cultivars Differing in Salt Tolerance
The effect of reduced osmotic potentials on germination and early seedling growth of four rice cultivars differing in salt tolerance were studied using iso-osmotic solutions (0, -0.232, -0.457, -0.677, -0.906 and -1.129 MPa) of NaCl and polyethylene glycol (PEG 4000). Seed germination and early seedling growth were assessed using four replicates of 25 seeds at 21±10C in the dark using paper towel method. Onset of germination, germination rate and seedling growth, all declined with increasing concentrations of both NaCl and PEG, the former being more inhibitory. Germination and growth processes were mainly affected at and above -0.457 MPa osmotic potential in both NaCl and PEG. Rice cultivars differed greatly in their tolerance to salt and water stress. However, the differences were well pronounced in NaCl but less so in PEG. The imposition of water stress by PEG for 9 days did not permanently inhibit germination or induce dormancy. However, salt stress appeared to be lethal than the equivalent osmotic potentials of PEG. Salt tolerant cultivars (V2 and BR23) performed consistently better under salt stress and consistently poor under osmotic stress compared with salt sensitive cultivars (V1 and IR8). These results suggested that the salt tolerance of rice cultivars is probably determined by their ability to withstand excessive Na+ and Cl‾ ions rather than their ability of water stress tolerance.
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