Effect of Water Stress on Grain Growth and Assimilate Partitioning in two Cultivars of Wheat Contrasting in their Yield Stability in a Drought-Environment

Grain growth pattern and grain weight in relation to its position between and within spikelets showed assimilate limitation to be a factor reducing grain yield in wheat plants grown on stored moisture in the field. Estimation of the relative contribution of pre- and post-anthesis assimilates to grain yield by a 14C labelling technique indicated that cultivar C 306, known for its stability in yield and drought-tolerance, was characterized by substantial mobilization of pre-anthesis assimilate (P), both in irrigated (24 per cent) and unirrigated (33 per cent) plants. As against this, in Kalyansona, a high yielding cultivar with moderate stress tolerance, the contribution of P to grain yield was only 13 and 22 per cent in irrigated and unirrigated plants, respectively. The mobilization of amino acids, estimated from nitrogen contents at anthesis and maturity, was decreased by water stress and was accompanied by a corresponding increased transport of carbohydrates.