Abstract
Global climate model predicts frequent and severe drought in the future resulting in limited crop production affecting growth and yield. The extent of drought tolerance in two wheat cultivars (WMRI-1 and BARI GOM-33) was investigated by foliar application of abscisic acid (ABA) and glycine betaine (GB) at the anthesis and grain filling stages. A pot experiment maintaining completely randomized design with four replications was set in the field laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh. A total of four treatments were followed such as i) Control (20–22% moisture content) ii) Drought (8–10% moisture content) iii) Drought + ABA and iv) Drought + GB. The plants at the reproductive stage were sprayed weekly with ABA (20 µM) and GB (50 mM) under drought conditions. Drought stress significantly declined chlorophyll content and photosynthetic rate in comparison to control. However, the foliar application of ABA and GB under drought considerably increased the rate of photosynthesis and pigment contents in the flag leaves compared to the plants grown under individual drought conditions. A considerable increase in lipid peroxidation and H2O2 contents in flag leaves were recorded in all drought conditions, while these values were reduced in ABA and GB treatments. ABA and GB application significantly enhanced the catalase and peroxidase enzymes activities and total antioxidant capacity exhibiting reduction in oxidative damage and increased grain yield. Heatmap using stress tolerance index (STI) showed that Drought + ABA and Drought + GB secured higher STI scores suggesting a greater degree of drought tolerance in both cultivars. In conclusion, foliar spraying of ABA and GB enhanced drought tolerance in both wheat cultivars by altering physiology and antioxidative defense suggesting a declined state of oxidative damage with increased yield.