Improving Photosynthetic Performance of Bread Wheat under Field Drought Stress by Foliar Applied Glycine Betaine

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Nineteen bread wheat genotypes were selected to examine the effect of glycine betaine (GB, 100 mM) on various photosynthetic gas exchange parameters under drought stress and to study the relationship of these parameters with non-enzymatic antioxidants. Drought stress caused a significant decline in net CO2 assimilation rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci) and transpiration rate (E) among the studied wheat genotypes, with the tolerant genotypes characterized by higher net photosynthetic rate, lower drought susceptibility index (DSI), and higher maintenance of glutathione content (GSH) and ascorbic acid (AsA) levels than the sensitive ones. GB application significantly improved the photosynthetic characteristics, particularly Pn and gs, of studied wheat genotypes which could be due to more utilization of glutathione and increased levels of ascorbic acid in flag leaves under drought stress. But this response was observed to be genotype specific. Positive correlation of AsA with DSI in GB treated plants, and of Pn with GSH under drought stress and GB applied conditions suggested the role of these non-enzymatic antioxidants in sustaining photosynthetic efficiency and yield stability under prolonged field drought stress conditions.