Root Development and Water-uptake under Water Deficit Stress in Drought-adaptive Wheat Genotypes

Drought adaptation of wheat is one of the most significant and complex subjects in the rain-fed agricultural regions of West Asia. Interaction between root water-uptake and the remaining soil moisture is a key factor for drought adaptation. Under controlled conditions, root development was compared among four wheat genotypes under water deficit stress in relation to water-uptake. In addition, the effects of soil water deficit on the production of biomass and grain were examined using drought-adaptive varieties from different sources. Genotypic differences in root development were significant by the time of heading under well-irrigated conditions but were decreased under water-stressed conditions. After heading, water deficit stress also decreased grain yield through a reduction in grain number. Genotypic variations in transpiration efficiency and harvest index, two components of water-use efficiency, were significant and transpiration efficiency was negatively associated with root weight and water-uptake. The effect of harvest index was three-times greater than that of transpiration efficiency. Two wheat genotypes, SYN-10 and Drysdale derived from different sources, had high grain weights in contrast to reduced root development and low water-uptake under water deficit stress. Their differences in genetic mechanism remain uncertain. Transpiration efficiency and harvest index are critical factors for producing greater grain yield under water deficit stress. These components are closely related and highly dependent on wheat genotype. Harvest index was more determinant of grain yield than transpiration efficiency. The drought-adaptive wheat genotypes achieved water-savings through reduced root weight and reduced water-uptake and compensated for these through higher transpiration efficiency and higher harvest index.