Abstract
Interspecific differences in drought tolerance were studied by two solution- and one field-culture experiments in a glasshouse using Japanese millet, sorghum, pearl millet and maize. Water stress treatment for the solution culture was achieved by adding polyethylene glycol 6000 to the solution at a final concentration of 200g/1000g H2O, producing a -0.93 MPa osmotic potential, while that for the field experiment was by suspension of watering. The treatment was made for about two weeks in the vegetative growth stage. Growth parameters and leaf water status were determined at the beginning, during and after the treatment. Dry weight of plant was generally decreased less by stress in pearl millet and sorghum, while the recovery after removal of stress was faster in sorghum and Japanese millet than in the other opecies. Osmotic potential (π) as against water potential (Ψ) in stressed leaves decreased more than in the control, except for maize. The decreasing order of relative water content with a decrease of either Ψ or π was as follows : maize>Japanese millet>sorghum>pearl millet. Osmotic adjustment (OA) increased in the following order : sorghum>Japanese millet>pearl millet>maize. From these results, we concluded that sorghum and Japanese millet, especially sorghum, possess a higher dehydration tolerance due to a higher OA and pearl millet due to a larger water retention ability, whereas maize easily wilts because of a smaller OA and water retention ability.
