Response of wheat and barley during germination to seed osmopriming at different water potential

Pre-sowing osmotic seed treatments were evaluated as a means of improving water uptake and germination performance of wheat (Triticum durum L. cv. Hourani-27) and barley (Hordeum vulgare L. cv. ACSAD 176) under four levels of water potential (0, -0.4, -0.8 and -1.2 MPa) created by using polyethylene glycol 8000. Seeds were osmoprimed in aerated solutions of 0.0, 0.2, 0.4 or 0.6 M KCl at 24 +/- 2 degrees C overnight and then rinsed and dried. Rate of water uptake by seeds was higher in osmoprimed than untreated seeds of both crops regardless of the water potential level. Decreasing water potential (more stress) adversely affected rate of water uptake in seeds of both crops. Seeds osmopriming increased germination percentage and decreased time to 50% germination at high water potentials (low stress), whereas the germination at low water potentials (more stress) was not affected by osmopriming treatments. The effect of osmopriming on rate of water uptake, germination percentage, and time to 50% germination was more pronounced in wheat than in barley. Reduction in the lag time of imbibition may be accounted for in part by some germination rate enhancement in the osmopriming treatments. Fresh weight and length of shoots (plumules) and roots (radicles) were enhanced in osmoprimed seeds in comparison to untreated seeds, in both crops at high water potentials (0 and - 0.4 MPa). As water potential in the medium decreased, these traits were inversely affected regardless of osmopriming treatment. Longer roots in wheat compared to barley were noted in the positive osmopriming treatments at high water potentials (0 and -0.4). These results might indicate that wheat is more responsive than barley at relatively high water potentials to osmopriming through rapid penetrating root system.