RESPONSE OF 4 SORGHUM LINES TO MID-SEASON DROUGHT .2. LEAF CHARACTERISTICS

Four sorghum lines were visually selected on the basis of degree of leaf desiccation for resistance and susceptibility to mid-season drought stress. An association between leaf-rolling and degree of resistance based on this method of selection had previously been observed, prompting this study to identify the physiological contribution of characteristics at the leaf level to mid-season drought resistance. During the drought period, the resistant lines showed more leaf-rolling than the susceptible lines, reducing the effective area of the uppermost leaves by about 75%. Leaf-rolling in the resistant lines occurred over a very narrow range of leaf water-potentials (-2.0 to -2.2 MPa) compared to the susceptible lines. The strong correlation between the light-extinction coefficient k and leaf-rolling indicated that changes in k over the season were in part due to differing abilities of the lines to roll their leaves. However, expected differences in leaf temperature between lines due to radiation shedding were not found. Lines exhibiting leaf-rolling had higher leaf conductances, although transpiration rates per unit leaf area were similar. It is suggested that leaf-rolling may alter the leaf surface microclimate so that stomata may remain open and growth continue without associated high rates of water loss.