Effects of deficit irrigation management on physiological and biochemical properties of two safflower cultivars

Introduction
Drought is one of the major environmental stress induced by global climate change that adversely affects the growth and development of plants and causes significant yield losses in the oil seed crop, safflower. Drought stress adversely impacts growth and productivity with various physiological and biochemical processes such as stomatal conductance, photosynthesis, chlorophyll content, carbohydrate metabolism, lipid peroxidation, and antioxidant defense system. As, the water resources used for irrigated agriculture are decreasing in many agricultural regions of the world, therefore, irrigation management under water scarcity is increasingly important. Various deficit irrigation management strategies have been developed in different agroclimatic regions to improve crop performance under water deficit conditions. However, It is very important to develop crop management strategies that make plants suited for stressful environmental conditions

Material and Methods
In order to study of deficit irrigation management on physiological and biochemical traits of two safflower cultivars, a field experiment was carried out in a split-plot arrangement in a randomized complete block design with three replications. The experimental site (32° 22' N, 48° 07' E), was located at Shahid Chamran University of Ahvaz, with a subtropical hot desert climate. Main plots consisted of four irrigation regimes including; control (irrigation treatments: 80%, 80%, 80%, and 80% of field capacity), mild (irrigation treatments: 60%, 80%, 80%, and 40% of field capacity), moderate (irrigation treatments: 60%, 60%, 60%, and6% of field capacity) and severe (irrigation treatments: 40%, 60%, 60%, and 60% of field capacity), and sub-plots consisted of two sunflower cultivars including; Padideh and Goldasht. Irrigation treatments were applied at stem elongation, branching, flowering, and grain-filling stages.

Results & Discussion
Deficit irrigation caused a significant reduction in stomatal conductance, photosynthetic rate, chlorophyll index, grain, and oil yield, but increased catalase and peroxidase enzyme activities, carbohydrate and malondialdehyde concentrations. Goldasht cv. with the highest stomatal conductance, photosynthetic rate, chlorophyll index, catalase, and peroxidase enzyme activities, carbohydrates concentrations, and with the lowest malondialdehyde concentrations and oil percentage had the highest economic oil and grain yield and it is recommended in a water-limited condition. The highest levels of antioxidant enzyme activity and lowest malondialdehyde content under water deficit conditions may provide better drought tolerance in this cultivar. The oil yield of both cultivars significantly decreased under moderate and severe heat stress by 31, 43, and 63%, respectively, when compared to the control. Goldasht cv. with a higher grain yield showed a higher oil yield.

Conclusion
Different irrigation regimes applied at different growth stages differently influenced the physiological and biochemical characteristics of safflower cultivars. The developmental stage and severity of water deficiency played an important role in cultivar responses to deficit irrigation regimes. Totally, a moderate deficit regime led to a 43% decrease in oil yield, but by saving about 40% of available water, this treatment is recommended as a suitable strategy for water management to reduce water use in this area.

Acknowledgements: Acknowledgments: We are grateful to the Shahid Chamran University of Ahvaz for the financial support of this project.

Keywords: Antioxidant activity, chlorophyll index, drought stress, malondialdehyde, stomatal conductance

References
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