Evaluation of drought stress indices in surface deficit irrigation of new sesame cultivars

Environmental stresses are a major obstacle to world food supply. There is relatively little stress-free arable land where crops reach their potential yields. For example, about 45 percent of the world's agricultural lands, with 38 percent of the world's population, are experiencing temporary or permanent drought (Bot et al., 2000). Sesamum indicum L., due to its tolerance to drought and heat, is very important in the development of arid and semi-arid regions as summer crop (Aien, 2013). In one study, sesame cultivar Darab 14 based on MP, TOL, SSI, HARM and STI indices was introduced as superior cultivar under normal conditions and moisture stress (Amani et al., 2012). Due to the importance of sesame as one of the most important edible oil products supplier in Iran, deficit irrigation can be adapted to water shortage during drought. Due to its high content of sesame oil (42-52%) and its good quality (low cholesterol and some antioxidants), it plays an important role in human health and on the other hand, it is tolerant and drought tolerant (Afshari et al., 2014). The purpose of this study was to investigate the effect of drought stress by applying different levels of surface irrigation and identifying superior cultivar based on stress indices.

Study and evaluation of drought stress indices in surface irrigation on sesame seed yield and its components, seed oil yield, seed oil percentage and water use efficiency of experimental seed were conducted at Behbahan Agricultural Research Station in 2014. The experiment was conducted as split plot in a randomized complete block design with 3 replications. Irrigation at two levels (irrigation after 100 and 200 mm evaporation from Class A pan, respectively) was evaluated as main factor and cultivar at 5 levels (local of Behbahan, SG37-92138, SG51-92138, SG53-92138 and SG55-92138) as sub-factor.

Comparison of mean water use efficiency in irrigation and cultivar interactions showed that 100 mm evaporation from Class A pan and V5 (SG55-92138) evaporation with water use efficiency of 0.272 kg/m3 sesame seed was superior. The mean water consumption in one year of experiment in 100 and 200 mm evaporation from Class A pan was 547.5 and 438.6 mm, respectively. The results of Pearson correlation coefficient showed the highest correlation of 1000 kernel weight after number of kernels per capsule with grain yield was r = 0.9616 which indicates the effective role of 1000 kernel weight gain in enhancing grain yield. The highest values of STI, MP, GMP, HM and YI were calculated with V5 (SG55-92138) with values of 1.538, 1037.1, 1024.7, 1011.5 and 1.548, respectively. Increasing of the above indices in cultivar V5 (SG55-92138) compared to other cultivars caused it to be introduced as superior treatment for drought stress. The decreasing trend of sesame yield caused by dehydration stress decreased SSI, MP and TOL indices and, on the contrary, decreased sesame yield, and led to bullish changes in STI, GMP, HM, YI and YSI indices.

Comparison of mean interaction effects between irrigation and cultivar in terms of water use efficiency showed that water use reduction in stress treatment decreased water yield in these treatments compared to non-stress treatment. The effect of reducing water use was even to the extent that it failed to cover the continuous decrease in yield in return for water consumption and continued to treat 100 mm evaporation of Class A pan despite more water consumption than the 200 mm evaporation treatment of Class A pan. The highest water use efficiency among treatments was due to increased yield.