Physiological Response of Cumin to Times and Type of Stress Modulator in Rain-Fed and Irrigated Conditions

Abstract

An experiment was conducted in a split plot factorial design with 3 replications for evaluating the physiological responses of cumin (Cuminum cyminum L.) to different times and types of stress modulators under rain-fed and irrigated conditions. The main factors included cultivation method at the 2 levels of rain-fed and irrigated conditions and foliar application times (once in the vegetative phase and twice in the vegetative and flowering stages) and sources of stress modulators at the 4 levels of control, 1.5 M glycine betaine (GB), 10–7 mM brassinosteroids (BRs), and 1.5 μM sodium nitroprusside (SNP). The rain-fed cultivations included more carotenoids, H2O2, proline, GB content, catalase, superoxide dismutase, and guaiacol peroxidase activities and less chlorophyll a, while further chlorophyll b appeared in the irrigated cultivations. The application times had no significant effects on the plant’s physiological attributes. Both in the rain-fed and irrigated conditions, foliar applications of BRs increased the activities of enzymatic or non-enzymatic antioxidants in cumin as compared to the other osmotic modulators. Under the rain-fed conditions, spraying of BRs increased the contents of chlorophyll a, chlorophyll b, carotenoids, and proline and catalase, superoxide dismutase, and guaiacol peroxidase activities compared to the control, while decreasing H2O2 and glycine betaine contents. Under the irrigated conditions, the amounts of chlorophyll a, chlorophyll b, carotenoids, proline, and GB and catalase, superoxide dismutase, and guaiacol peroxidase activities enhanced, whereas H2O2 content were lowered in comparison to the control. Overall, the applied modulators could be classified as brasinosteroids > glycine betaine > sodium nitroprusside in terms of reducing drought stress impacts through their modulatory effects of enhancing enzymatic antioxidant activities.