Responses of spring wheat exposed to pre-anthesis water stress

Abstract

Spring wheat cv. Yecora 70 was exposed to soil water deficits during three phases between emergence and anthesis: early (22 days after sowing to terminal spikelet), mid (terminal spikelet to anthesis) and late (early boot to anthesis). The objective was to quantify the effects of water stress on partitioning of above-ground biomass to the spike, the ratio between kernel number and anthesis spike weight, canopy expansion, radiation interception and phenology. This information can be used to test the assumptions used when modelling wheat growth and yield under water-limiting conditions. The extension rate of the lamina and pseudostem was reduced when more than 50% of the extractable soil water had been extracted from the root-zone, independent of the stage when stress was imposed. Stress reduced biomass accumulation more through a reduction of the amount of radiation intercepted than reduced radiation-use efficiency. The reduction in the amount of radiation intercepted was due to lower leaf area index, as the radiation extinction coefficient was similar under stress and non-stress conditions. Stress treatments reduced spike biomass at anthesis to 58-94% of that in the well-watered control, but had little effect on the pattern of biomass partitioning to the spike and the proportion of anthesis biomass as spike. Stress after terminal spikelet reduced the ratio of kernel number to anthesis spike weight by 50%, suggesting that reduced kernel number under stress may not be solely due to a restricted assimilate supply. This study showed that current assumptions are valid regarding the response of wheat to pre-anthesis stress in terms of canopy expansion, radiation interception and biomass partitioning to the spike. However, the constancy of the ratio of kernel number to anthesis spike weight was shown not to hold under water stress.