Use of water use efficiency and water stress tolerance indices for the comparing of bread wheat (Triticum aestivum) genotypes

Bread wheat (Triticum aestivum L.) is one of the most important cereals worldwide and is being grown in many areas of the world. However, there is a lack of information about using the proper stress index to determine the tolerance of wheat cultivars to water stress. A two-year field study was conducted with the objective of determining the effect of different rates of nitrogen (N) (control, 80 kg N/ha, and 160 kg N/ha) and two irrigation treatments (non stressed and post anthesis water stressed) on three bread wheat cultivars. Water deficit markedly affected grain yield, straw yield, and harvest index. Under water deficit grain yield was reduced by 58%, showing that wheat cultivars were sensitive to drought stress. Tolerance (TOL) index was lower under water deficit than well watered (WW) conditions in both years. Stress Tolerance Index (STI), Mean Productivity (MP), and TOL indices were efficient in evaluating the sensitivity to drought stress. Grain yield under stress condition showed positive correlation with STI, MP and TOL indices. Water use efficiency and irrigation water use efficiency increased with increasing the N rates in WW treatment but decreased in WD treatment. In general, for the most efficient use on both N and water, the supply of one should be adjusted to that of the other. If irrigation is for maximum yields, fertilization should be too; but if irrigation is limited, the fertilizer supply should be adjusted accordingly to prevent N loss and pollution of the environment.