The objectives of this study were to evaluate: 1) The relationship among yield and yield components, and 2) the effectiveness of several drought resistance indices under various water regimes. Grain yield under irrigated conditions was adversely correlated with yield under non-irrigated conditions. The grain yield of wheat was associated with the larger number of grains per unit area under both conditions. The results suggested that the larger number of grains/spike under irrigated condition and the higher grain weight and larger number of spikes per unit area under non-irrigated condition should be selected to increase grain yield. Among the indices, MP, GMP and STI were more effective in identifying high yielding cultivars in both drought-stressed and irrigated conditions (group A cultivars). Under severe stress, none of the indices used were able to identify group A cultivars, although regression coefficient (b) and SSI were found to be more useful in discriminating resistant cultivars. It is concluded that the effectiveness of selection indices in differentiating resistant cultivars varies with the stress severity.value and b) have been employed under various conditions. The present study was conducted to evaluate the relationship among yield and yield components, and to test the effectiveness of drought resistance indices in eleven wheat cultivars under various stress conditions over three years.
