Evaluation of Water Deficit Stress on Seedling Growth, Antioxidant Enzyme Activity and Yield of Four Cultivars of Cotton

Cotton (GossypiumhirsutumL.), is an indeterminate perennial, oilseed and ?ber crop. Water availability and quality affect the growth and physiological processes of all plants. In order to investigation of drought stress on germination, physiological and agronomical traits of cotton a study was done in laboratory and greenhouse condition. In laboratory study an experiment was planned with two factors (variety and drought stress) as a factorial experiments based on completely randomized design with 4 replications. Osmotic potentials were conducted with D-Mannitol (0, -0.4, -0.8 and -1.6 Mega Pascal) and Germination characteristics were studied. Green house experiment was done at 25×5.5 cm pots. Control, medium stress and high level of stress were known as 75, 15 and 5% relative soil water content. The effect of drought on total of germination was significant. The highest value of this trait was obtained in control and the lowest of that was related to -1.6 Mpa. Total germination of Golestan was the highest. Sahel has the least total germination. The effect of drought stress levels was significant on all agronomy traits except stem fresh weight. Based on LSD test of drought stress levels on agronomy traits, with increasing of stress all traits were decreased. Maximum of root length was observed in 75 % of field capacity (75%FC=control) and minimum of it was obtained in 5%FC (8.55). LSD test of cultivars showed that the Sahel has the best performance of agronomy traits, as the highest of root length and dry weight, leaf fresh weight, height, total dry weight were observed in Sahel. With increasing in drought stress from control to higher level of stress, leaf area index (LAI) was decreased. The results of Duncan test showed that in totally with increasing of stress level LAI, super oxide dismutase, stomata conductance and photosynthesis (Phn) almost were decreased and catalase (CAT), acrobat peroxidase (APX) and fv/fm (quantum yield) were increased. CAT was decreased as stress level was increased. As the same, minimum of APX was obtained in control and maximum of it was related to the high level of stress. Stomata conduction was decreased as stress level was increased. Phn also was decreased as stress level was increased.