Many wheat (Triticum aestivum L.) production regions are threatened annually by drought stress. Carbon isotope discrimination (Δ) has been identified as a potentially useful trait in breeding for improved drought tolerance in certain environments. Broad use of Δ as a selection criterion is limited, however, mainly due to an inconsistent relationship observed between grain yield and Δ and, to a lesser extent, because of the high resource demand associated with phenotyping. The efficiency of selection may be improved by the identification and verification of molecular markers for use in marker-assisted selection (MAS), and a reliable relationship to grain yield may be established based on a location’s total amount and distribution of precipitation over the growing season. Given the environmental variability in precipitation dynamics, it is necessary to evaluate this relationship in target breeding environments. In this study, grain Δ was collected on a panel of 480 advanced soft white winter wheat varieties grown in five Pacific Northwest environments. A genome-wide association study approach was used to evaluate the amenability of grain Δ to MAS. The genetic architecture of grain Δ was determined to be characterized by multiple, small effect marker-trait associations with limited repeatability across environments, suggesting that MAS will be ineffective at improving Δ selection efficiency. Further, the relationship between grain yield and Δ ranged from neutral (r=‐0.01) to moderately positive (r=0.44) in the target environments. Such moderate correlations, coupled with variability in this relationship, indicate that direct selection for Δ may not be beneficial.

No abstract

A major obstacle in the effort to develop drought tolerant varieties of wheat (Triticum aestivum L.) is phenotyping. Traits known to contribute to improved drought tolerance, such as water-use behavior, reliance on stem reserve carbohydrates, and the ability to develop deep roots, require time and resource-intensive screening techniques. Plant breeding programs often have many thousands of experimental genotypes, which makes testing for each of these traits impractical. This work proposes that carbon isotope discrimination (∆) analysis of mature grains may serve as a relatively high-throughput approach to identify genotypes exhibiting traits associated with drought tolerance. Using ∆ as a proxy for stomatal conductance and photosynthetic capacity, assumptions can be made regarding fundamental plant physiological responses. When combined with knowledge of the terminal drought severity experienced in a particular environment, genotypes exhibiting conservative and rapid water use, deep roots, and reliance on stem reserve carbohydrates may be identified. Preliminary data in support of this idea are presented. Further verification of this use for grain ∆ will better equip wheat breeding programs to develop more drought tolerant varieties.

The water‐limited potential yield of wheat (Triticum aestivum L.) may be largely dependent on plant transpiration behavior. Research into plant transpiration dynamics is limited due to the difficulty of monitoring water use over an extended period of time. The advent of fully automated gravimetric platforms makes this research possible. The methods for using this equipment to study transpiration of wheat in water‐deficit environments are not well established. The objective of this greenhouse study was to develop a methodology to evaluate plant transpiration under terminal water stress using a gravimetric platform. Using a plant–pot system designed to limit nonplant water loss, the methodology proved capable of monitoring plant transpiration over a 42‐day period and detected significant differences between well‐watered and water‐stressed treatments. However, the high degree of variation in transpiration limited the system's ability to detect significant differences between genotypes of similar watering regimes. Both environmental and human error likely contributed to the observed variation. Recommendations are provided to reduce this variation and improve upon the methodology for future studies. This work lays the foundation for further research into plant water use and the identification of genotypes capable of high transpiration despite exposure to water‐deficit conditions.