**Abstract**

Water stress is a major production constraint in agriculture worldwide. Efforts to breed for drought tolerance are invariably hampered by the amount of time required to phenotype a large number of individuals and poor or inconsistent correlations and multiple mechanisms involved. Canopy temperature depression has emerged as a potential surrogate in view of substantial natural variation in crops as well as its correlation with yield. Based on the experimental findings two types of ideotype models based on CTD have been proposed as isohydric ("water saving") and anisohydric ("water spending"). The isohydrics have advantage in the harsher environments, whereas the anisohydrics perform better under moderate/ mild drought situations. Water savers have a shallow root system with intermediate root growth and thin roots. They are early and have high water use efficiency, reduced transpiration and limited leaf area and canopy biomass development and superior photosynthate remobilization to pod and grain. Contrary to this, water spenders have a vigorous and deep rooting system with rapid root growth and a thicker root system. Such genotypes are early and have highly effective water use, moderate transpiration and fast leaf area and canopy biomass development, moderate sink strength and superior photosynthate remobilization to pod and grain formation.

**Keywords:** drought stress, physiology, canopy temperature depression
