Sole and combined foliar application of silicon and putrescine alleviates the negative effects of drought stress in maize by modulating the morpho-physiological and antioxidant defence mechanisms

Drought stress is one of the major threats to food security in the climate change scenario. Reducing the deleterious impacts of drought stress on the productivity of cereal crops is crucial. Hence, limited information has been available about the effect of the combined use of plant growth regulators and mineral fertilisers on promoting drought tolerance in maize seedlings. In this study, a pot experiment was carried out to evaluate the potential of sole or combined application of silicon (Si) and putrescine (Put) to mitigate the detrimental effects of drought on maize. The experimental treatments were, i.e. control (CK), water spray, 4.0 mmol Si, 0.5 mmol Put, and 4.0 mmol Si + 0.5 mmol Put on maize crop grown at two different water-holding capacity levels (80% well-water condition and 40% drought stress). The experiment was arranged in a complete randomised design with factorial arrangements having three replications. Exposure of maize plants to drought stress at the reproductive phase (VT-tasseling) reduced the photosynthetic pigments, including chlorophyll a, chlorophyll b and chlorophyll a + b, relative water contents, leaf area, yield and yield attributes. However, foliar application of Si and Put individually and Si + Put dramatically reduced these negative effects by improving photosynthetic pigments, relative water contents, and activities of enzymatic antioxidant defence. Drought stress-induced lipid peroxidation in the form of more production of malondialdehyde content, hydrogen peroxide and electrolyte leakage significantly declined due to the combined application of Si and Put compared to the respective control. Drought stress boosted the activities of key enzymatic antioxidants (catalase, superoxide dismutase, peroxidase, and ascorbate peroxidase) irrespective of the treatment application. Moreover, it was noted that the accumulation of osmolytes (proline and soluble protein) contents was increased by the combined application of Si and Put. Under drought stress conditions, combined foliar application of Si and Put considerably improved 22.70% cob length, 12.77% number of grains per cob, and 18.30% 100-grain weight, which ultimately enhanced maize's 10.29% grain yield. From the current study's findings, it was concluded that a combined foliar spray of silicon and putrescine at the reproductive phase is an effective strategy to enhance the maize yield in drought-prone areas.