Interrelations of some Antioxidants, Physiological Characteristics and Grain Yield of Sesame (Sesamum Indicum L.) Under Different Irrigation Regimes

Water deficit stress is the most important environmental constraint for growth, yield and productivity of crops, including the oil seed crops. This study was aimed at studying the influence of differing irrigation régimes on growth, chlorophyll , proline and some antioxidants content along with grain yield, yield components and oil content of sesame genotypes using a 4-replicate split plot randomized complete block design at Shervedan Research Farm, Isfahan University of Technology, Iran in 2009. Irrigation levels based on evaporation from a standard class-A pan served as main plots and included I1 as control (75 mm), I2 as moderate stress (110 mm) and I3 as severe stress (145 mm). Four sesame genotypes served as sub plots and included Oltan, Naz-Takshakheh, Varamin and Yekta. Leaf chlorophyll, proline, catalase (CAT) and ascorbate peroxidase (APX) antioxidant content, leaf area index (LAI) at pod formation, pod/plant, seed/pod, 1000-seed weight, grain and biological yield and oil percent were measured. The I1 and I3 irrigation levels produced the greatest (2.53) and smallest LAI, respectively. I1 level of irrigation out yielded the I3 level in terms of pod/plant, seed/pod and grain yield by 44% (91.97), 14% (54.78) and 28%(1481.02 kgha-1), respectively. I1 and I3 levels of irrigation indicated the greatest (7397.4 kgha-1) and smallest (5890.4 kgha-1) biological yield, respectively. I2 level of irrigation led to 35% and 40% increase in CAT and APX but I3 decrease the activity of the latter enzymes by 29% and 11% respectively, compared to the I1 level of irrigation. It could be concluded that severe water deficit decreases grain yield and growth of sesame genotypes, and the reduction is mainly due to the photosynthetic surfaces, rather than chlorophyll concentration. It seems that CAT and APX play significant antioxidative roles under moderate water deficit, but they cannot play such a role when sesame genotypes are severely stressed.