There is a lack of studies that have investigated grain yield, its components and photosynthesis in late stages of wheat growth, giving us insufficient understanding of how these factors interact to contribute to yield during this period. As a result, three field experiments were carried out examining 20 winter wheat genotypes of diverse origins under irrigated, terminal drought and dryland conditions in the southern Idaho. Our objective was to evaluate the interaction between post‐anthesis physiological traits, especially leaf‐level photosynthetic capacity, senescence and yield components on grain yield in different moisture regimes. Genotype differences were found in leaf‐level photosynthesis and senescence, canopy temperature depression, grain yield and yield components in each water regime. Grain yield was closely associated with traits related to grain numbers. In all three moisture regimes, positive correlations were observed between grain yield and photosynthesis that were dependent on the timing or physiological growth stage of the photosynthetic measurement: highly significant correlations were found in the mid‐ and late grain filling stages, but no correlations at anthesis. Consistent with these findings, flag leaf senescence at the late grain filling stage was negatively correlated with grain yield and photosynthetic rate (under terminal drought and dryland conditions). These findings provided evidence that grain yield was sink‐limited until the final stages of growth, at which time sustained photosynthesis and delayed senescence were critical in filling grain. Because the trends were consistent in moisture sufficient and deficient conditions, the results suggest that late‐season photosynthesis and delayed leaf senescence are driven by the size of the reproductive carbon sink, which was largely governed by factors affecting grain numbers.

Wheat accessions from the USDA-ARS National Small Grains Collection (NSGC) are a potential genetic resource for variety improvement. This study assessed the agronomic performance and drought tolerance in 198 winter wheat accessions under irrigated and terminal drought environments in the 2012–2013 season, and repeated the test under terminal drought only during the 2013–2014 season. The 198 accessions were classified into three maturity groups, early, intermediate, and late based on heading data. In all three environments, the early accessions had the best agronomic performance, produced higher grain yield, thousand-kernel weight and grain volume weight, and had earlier heading date and shorter plant height. The intermediate accessions had similar grain yield and thousand-kernel weight as the early accessions in the irrigated environment, but had lower thousand-kernel weight in the terminal drought environments. Terminal drought had significant effects on grain yield, plant height, thousand-kernel weight, and grain volume weight. The positive correlation between GY and HD suggests that the ‘late early’ types in the early maturity were the most successful. Out of 198 accessions evaluated, twenty-three had high yield stability and drought tolerance according to the drought susceptibility index and membership function value of drought tolerance. The eight of twenty-three accessions identified (four early and four intermediate) had high grain yield in three environments. Some of these accessions have been further used in bi-parental mapping studies and by breeders for grain yield and drought tolerance improvement.

Drought stress (DS) at different growth stages of spring wheat (Triticum aestivum L.) may affect its grain yield and end‐use quality differently. The impact of drought stress at different growth stages on yield has been widely studied, but the impact on grain quality has not been thoroughly investigated. A 2‐year field experiment was conducted to evaluate the effects of DS at different growth stages on end‐use quality and grain yield in different spring wheat classes (soft white ‘Alturas,’ hard red ‘Coho,’ and hard white ‘Dayn’). The treatments included DS (from tillering to stem elongation, booting to heading, and anthesis to soft dough) plus a fully irrigated (well‐watered) check. We found significant differences between the three wheat classes in most end‐use quality parameters. Relative to the well‐watered conditions, DS from tillering to stem elongation and from booting to heading did not affect grain yield and most end‐use quality parameters. Flour protein, lactic acid and sucrose solvent retention capacities, and mixograph peak time were more impacted by post‐anthesis DS. These changes in end‐use quality were correlated and, thus, directly or indirectly affected baking performance. Our results indicate that reduced irrigation at early growth stages can maintain grain yield and end‐use quality of spring wheat of different classes, for example, grain yield of 437 g m⁻² and flour protein of 13.2–16.4 g kg⁻¹ across different classes subject to DS at early growth stages compared to 379 g m⁻² and 13.9–17.9 g kg⁻¹ subject to post‐anthesis DS.