Response of Tunisian autochthonous pearl millet (Pennisetum glaucum (L.) R. Br.) to drought stress induced by polyethylene glycol (PEG) 6000

Seeds of pearl millet (Pennisetum glaucum (L) R. Br.) from six provenances of Tunisia were subjected to germination and shoot and root length tests on filter paper treated with polyethylene glycol 6000 (PEG 6000) solutions made up to provide osmotic potentials of 0, -1 and -2 MPa. Mean germination percent for all provenances decreased about 73% in -2 MPa compared to control (0 MPa) treatment. Osmotic potential of -1.0 MPa improves the rate of germination but not significantly compared to the control. There were significant differences among the relative germination percent of the provenances in different treatments. Decreases in the external osmotic potential induced decreased shoot growth while a slight increase in root length associate with the -1 MPa treatments was observed for some ecotypes. This reflects an adaptive response involving an increase in root length to reach deeper water in the soil. It was also notified that the elongation of the radicle is more sensitive to the osmotic constraint than the coleoptile.