Abstract
Wheat (Triticum aestivum L.) is one of the commonly planted crops in the world. In order to meet the requirement of increasing population and severe environment, it is essential to understand the effects of drought stress on wheat grain yield and quality. Grain development is supported by sources (e.g., stem reservation and photosynthesis), and drought stress affects both source capacities. Contributions to grain filling from either source have been well studied in wheat, but the interactive relationship between sources has not been thoroughly investigated. To identify the effects of temporal drought stress on source and sink capacities of wheat, field and greenhouse experiments were conducted to compare plant growth and yield in response to drought stresses. In addition, flour protein and gluten contents, solvent retention capacity (SRC), and baking quality were tested using the grain from the field experiment, to improve our understanding of the effects of drought stress on grain end-use quality and irrigation scheduling for maintaining grain quality. In both greenhouse and field experiments, four water regimes were applied: well-watered control as 100% of evapotranspiration (ET), drought stress (50%ET) from tillering to stem elongation, drought stress either from booting to heading in the field experiment or from booting to anthesis in the greenhouse experiment, and drought stress from anthesis to soft dough. The greenhouse had another treatment as 75% progressive drought. In both greenhouse and field experiments, significant differences in biomass (i.e., vegetative tissue and spikes), grain weight and grain yield were observed among water regimes. Grain yield of drought from booting to either heading or anthesis achieved the least reduction in both experiments, and positive correlations were found between grain yield and stem weight, plant height, and grain number. In the field experiment, different varieties (i.e., ‘Alturas’, ‘SY Coho’ and ‘Dayn’) showed significant differences among water regimes in different end-use quality parameters. Grain hardness was found positively correlated to protein content, water absorption, starch damage, and gluten strength in the three varieties. Loaf volume was positively correlated with mixograph peak time in SY Coho, while cookie diameter was negatively correlated with flour yield, grain hardness, and water, sodium carbonate, and sucrose SRC in Alturas. In this thesis, the growth stage from anthesis to soft dough was revealed as the most sensitive stage to drought stress in spring wheat. Insufficient moisture during this stage led to grain yield reduction and alteration in end-use quality. Such results will facilitate irrigation management for maintaining grain yield and quality in wheat production.