Foliar application of abscisic acid and glycine betaine induces tolerance to water scarcity in wheat

The global climate model predicts frequent and severe droughts 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 a 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) solutions 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 content in flag leaves was 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 enzyme activities and total antioxidant capacity, reducing oxidative damage and increasing grain yield. A hierarchical clustering heatmap using the stress tolerance index (STI) showed that Drought + ABA and Drought + GB secured higher STI scores, suggesting a greater drought tolerance in both cultivars compared to individual drought treatments. 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.