Effect of Water Deficit Stress on the Physiology, Growth and Leaf Cell Ultrastructure of Sorghum ( Sorghum bicolor r (L.) Moench)

An experiment was conducted in growth chambers to study the response of sorghum cultivars to water deficit stress. Seven sorghum cultivars were evaluated under three water deficit levels [control (-0.05 MPa), mild stress (-0.27 MPa), and severe stress (-0.96 MPa)] in a hydroponic culture in a completely randomised block design replicated three times. The three water deficit levels were created by adding 0, 10 and 20% (w/v) polyethylene glycol 6000 (PEG 6000) to the nutrient solution. The results indicated that water deficit, especially severe water deficit (-0.96 MPa), severely affected the growth and physiology of sorghum. Water deficit stress reduced plant height, leaf area, dry matter accumulation, water use efficiency, root length, and stomatal density. Water deficit stress increased stomatal closure and thus leaf diffusive resistance. Stressed plants deposited larger amounts of epicuticular wax on leaf surfaces and stomatal openings. Water stress significantly reduced the amount of starch grains in the chloroplasts. Sorghum cultivars displayed distinctive response to water deficit stress for many of the parameters. Jigurti, Gambella 1107 and Meko grew better than P9403 and SA1486 under water deficit conditions. Jigurti showed no significant reduction in any of the growth parameters even under severe water deficit (-0.96 MPa) conditions. Keywords : Epicuticular wax; Leaf diffusive resistance; Leaf relative water content; Starch; Stomata; Water use efficiency. Ethiopian Journal of Biological Sciences Vol. 5 (2) 2006: pp. 161-176