Enhancing Drought Tolerance and Water Productivity of Diverse Maize Hybrids (Zea mays) Using Exogenously Applied Biostimulants under Varying Irrigation Levels

Water deficit is a decisive challenge that tremendously affects maize physiological functions and productivity. Hence, it is crucial to ameliorate its tolerance to drought stress, in particular under abrupt climate change and a growing population. The present study aimed to explore the influence of exogenously sprayed moringa seed extract (Moringa oleifera) and a-tocopherol on physio-biochemical, morphological, and yield attributes of six diverse maize hybrids under three irrigation levels in poor-fertility sandy soil. The applied irrigation regimes were based on estimated crop evapotranspiration (ET) using the FAO Penman-Monteith equation. A split-split plot arrangement with a randomized complete block design and three replicates was applied for different treatments. Irrigation levels (100% ET, 75% ET and 50% ET) were established in the main plots, while foliar applications (moringa extract and a-tocopherol) were located in subplots and the assessed hybrids (SC162, SC166, SC167, SC168, SC176, and SC178) in subsubplots. Mild (75% ET) and severe (50% ET) drought stress gradually reduced the gas exchange, photosynthetic efficiency, water relations, and yield traits compared with well-watered conditions (100% ET). However, foliar application of moringa seed extract or a-tocopherol was effective in reinforcing maize tolerance to drought stress by enhancing the accumulation of osmoprotectants, improving antioxidant enzymes, and decreasing levels of peroxidation of membrane lipids and electrolyte leakage compared to untreated control. These positive impacts were reflected in boosting yield traits and crop water productivity under water deficit conditions. The physiological and agronomic performance of the assessed maize hybrids considerably varied under water deficit conditions. The hybrids SC168, SC176, and SC178 exhibited the best performance under mild and severe drought conditions compared with the other hybrids. Consequently, the integration of exogenously applied moringa seed extract or a-tocopherol with tolerant maize hybrids such as SC168, SC176, and SC178 is an efficient approach to ameliorating drought tolerance under water-scarce conditions in arid environments.