effects of drought stress and defoliation on sunflower (helianthus annuus) in controlled conditions

abstract in order to evaluate the effects of drought stress and defoliation on sunflower, a study was conducted under controlled conditions. treatments were a combination of three levels of drought ((100, 60 and 30 percent of field capacity (fc)) and three levels of defoliation (control, removal of either 4 or 6 leaves from lower part of the plant) laid out, in a completely randomized design with four replications. drought stress was applied from 4-leaf- stage up to the end of plant growth period while leaf removal was conducted at the heading stage. results indicated that drought stress affected most of the measured parameters. plant height, plant dry matter, stem diameter, head size, seed number/head, 100-seed weight and seed weight/ head declined upon drought stress as compared to control. spad readings increased as drought stress increased. defoliation caused an increase in spad and a decrease in seed number/head. leaf number was not affected by either drought or defoliation. keywords: defoliation; drought stress; plant height; seed weight; sunflower