ABSTRACT
Historical evidences have linked drought with the collapse of the Mayan civilization from 1020 to 1100 A.D. (Kennett et al. 2012). This statement tells the drastic effects of drought in very plain words and also cautions us to nd the ways to tackle this problem, which limits the food productions, for the benet of the future generations. Drought tolerance or resistance is dened as “the potential of a plant to display ower and produce an economic yield under limited supply of water” (Farooq et al. 2009). The viable components of drought resistance in plants include the avoidance as well as the tolerance to water-limited conditions. Plant mechanisms that contribute
21.1 Introduction ..........................................................................................................................405 21.2 Importance and Production of Wheat as a Major Small Grain Cereal Crop .......................407 21.3 International Institutes Working on Wheat Drought Resistance ..........................................408 21.4 Exploring Genetic Diversity for Drought Resistance ...........................................................409 21.5 Examples of Physiological Effects of Drought Stress on Crop Plants ................................. 410
21.5.1 Photosynthesis .......................................................................................................... 411 21.5.2 Growth Responses .................................................................................................... 411 21.5.3 Development ............................................................................................................. 412 21.5.4 Reproductive Processes and Crop Yields ................................................................. 412
21.6 Molecular Approaches for Obtaining Drought Resistance in Crop Plants .......................... 413 21.6.1 sRNAs Can Regulate the Gene Expression during Drought .................................... 413 21.6.2 Transcription Factors Can Regulate the Expression of Many Genes ....................... 414 21.6.3 Differential-Regulated Functional Genes and Proteins Provide Tolerance
to Drought Stress ...................................................................................................... 415 21.6.4 Overview of Gene Revolution Following Green Revolution .................................... 416
21.7 Understanding Drought Tolerance Mechanisms .................................................................. 416 21.7.1 Genetics and Molecular Approaches ........................................................................ 417 21.7.2 Genomics-Based Approaches ................................................................................... 418 21.7.3 Biotechnological Approaches ................................................................................... 418 21.7.4 Modeling Approaches ............................................................................................... 419 21.7.5 Root Studies .............................................................................................................. 420
21.8 Challenges and Future Perspectives ..................................................................................... 420 21.9 Concluding Remarks ............................................................................................................ 421 Acknowledgments .......................................................................................................................... 421 References ...................................................................................................................................... 421
primarily to the drought resistance in wheat are early maturity so that the crop ripens ahead of periods of drought stress; a vigorous and deep root system to efciently utilize the available soil moisture; an active mechanism that senses the water-limited environment and closes the stomata in response to the drought stress without hindering the photosynthetic output; a waxy layer on the leaf surface to reduce transpiration loss; and a complex mechanism in which the macromolecules and several small biological molecules such as proteins, nucleic acids (microRNA, RNA, and DNA), lipids, carbohydrates, free radicals, hormones, mineral elements, and ions play crucial roles toward making the plant to cope with the drought stress. Drought is also associated with various stresses, such as high temperatures, excess salt, acidity, cold, and alkalinity, and a number of physiological reactions including pathological reactions, growth, senescence, embryogenesis, development, wound healing, signal transduction, damage by UV-B radiation, owering, and many other processes. Hence, in general, drought stress is associated with nearly all features of biology of a plant (Hong-Bo et al. 2006).
