Wheat is a crucial staple food crop, and North America contributes significantly to global wheat production and exports. Rising temperatures pose a major threat to wheat yields, with projections indicating significant yield reductions per degree of warming. Adaptation strategies, such as replacing early-maturing varieties with late-maturing ones to extend the growing season, have been proposed. However, these are largely hypothetical and don't fully capture the real-world effects of variety adaptation. This study aims to benchmark current wheat breeding progress against historical climate trends to guide future breeding programs and improve our understanding of climate resilience in wheat.

Existing literature highlights the negative impacts of high temperatures on wheat, particularly during the flowering stage, leading to reduced grain yields. Modeling studies suggest adapting varieties to extend the growing season as a mitigation strategy. However, a comprehensive understanding of the effectiveness of current breeding strategies in enhancing climate resilience is lacking due to a scarcity of long-term field observations.

This study utilizes a large dataset (85,770 data points) from the Northern Regional Performance Nursery (NRPN), Southern Regional Performance Nursery (SRPN) for winter wheat, and Hard Red Spring Wheat Uniform Regional Nursery (HRSWURN) for spring wheat across 92 sites in the Great Plains of North America (1960–2018). The dataset includes yields for common check varieties (Kharkof for winter wheat, Marquis for spring wheat) and advanced breeding lines planted in the same trials each season. A fixed-effect regression model was used to analyze the relationship between yields and climate variables (freezing degree-days (FDD), growing-degree-days (GDD), extreme-growing-degree days (EDD), and precipitation). The impact of 1°C warming was estimated via bootstrap analysis. Future yield changes were projected using four Shared Socioeconomic Pathways (SSPs) and six climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6).

Analysis revealed that advanced winter wheat breeding lines showed a yield decline of 3.6% per 1°C warming, less sensitive than the check variety (−5.5%). This suggests improved climate resilience in winter wheat. In contrast, advanced spring wheat breeding lines displayed a 7.5% yield reduction per 1°C warming, slightly more sensitive than the check variety (7.1%), indicating a lack of improvement, or even a decline, in climate resilience. Future climate projections under SSP scenarios show yield declines for both winter and spring wheat, even with advanced breeding lines. The projected yield reductions are substantial, ranging from 12.7% to 47.2% for winter wheat and 24.8% to 62.7% for spring wheat in different SSPs by the end of the century. While advanced breeding lines showed yield gains relative to the check varieties under baseline conditions, these gains are projected to be offset, or even surpassed, by the negative impacts of warming in higher SSP scenarios.

These findings highlight that current wheat breeding strategies are insufficient to counteract the projected impacts of climate change. The contrasting responses of winter and spring wheat to warming likely stem from differences in their phenology and sensitivity to high-temperature extremes. The study's results are consistent with previous assessments derived from other data sources and modeling approaches. However, it contrasts with some modeling studies that oversimplify variety adaptation scenarios by assuming unchanging growing season lengths. The lack of improvement in climate resilience for spring wheat emphasizes the need for further research into the underlying genetic mechanisms involved in heat and cold stress responses.

This study empirically demonstrates that current genetic gains in wheat breeding may not offset the negative impacts of future climate change, especially for spring wheat. Mitigating climate change through reduction of greenhouse gas emissions and accelerating the development and adoption of climate-resilient wheat varieties are crucial to ensure future wheat production. Future research should focus on identifying key genetic determinants of heat stress tolerance and utilizing innovative breeding technologies to accelerate the development of adapted varieties.

The study does not account for the CO2 fertilization effect due to the uncertainty in estimating its impact on yield variability. The analysis focuses on historical breeding progress and may not fully capture the potential benefits of new breeding technologies such as speed breeding and genomic selection. The analysis is limited to rainfed conditions in North America and may not be generalizable to other regions or irrigation systems.