Physiology of Grain Yield in Wheat Growing on Stored Water

Abstract

The grain yield of wheat plants grown in the glasshouse on a fixed and limiting supply of water can be substantially increased by forcing the plants to use water slowly when young so that they have more water available while filling their grains. Water use was manipulated either (1) by providing the entire water supply at sowing and allowing the plant to develop only one root (instead of the usual 5-20) or (2) by metering the water to the plants at varying rates. With a water supply of 1800 ± 50 g per plant (equivalent to 180mm transpiration from a canopy containing 100 plants m^-2), the grain yield ranged from zero, for plants uncontrolled in water use, to 3.5 g per plant for plants left with at least 400 g water to use after anthesis. Plants which used less than 200 g water after anthesis had yields approximately proportional to the amount of water used, giving about 1 g grain per 80 g water (compared with 1 g dry matter per 200 g water for the whole plant). The high efficiency of water use for grain growth was apparent rather than real. It arose because the grain of severely stressed plants was filled largely (up to two-thirds) from reserves, rather than largely from current photosynthate.