Abstract
Two experiments were conducted to evaluate the effects of water stress applied at different growth stages, on the growth, yield components, and grain yield of spring wheat (Triticum aestivum L.) cultivars. The effects of water stress on growth and yield were smaller and recovery better when the stress was applied in the early vegetative phase than when applied in the late vegetative and post-anthesis stages. Water stress occurring in the early vegetative phase decreased tiller production, but this was compensated by production of late tillers after rewatering. A water stress occurring during growth stages 32-65 days decreased spikelet fertility and the number of grains per ear which was the greatest contributor to the reduction in yield. Other components, however, such as number of ears per unit area also contributed to the reduction in yield. There were highly significant genotypic differences in absolute grain yield and yield stability under water stress and awns appeared to be crucial in this respect. Overall, water stress had a greater effect on yield when it occurred during the reproductive stage and it is suggested that screening for water stress tolerant genotypes in cereals should be done at the reproductive stage.
