Abstract/Summary

Low water availability is a limiting factor for wheat production in arid/semi-arid western prairies. This study characterized the Canadian heritage bread wheat panel for physiological traits, yield attributes, spectral indices and seed characteristics. Stomatal, flag leaf, and transpiration-related traits were studied. Most morpho-phenological traits, physiological parameters, and stomatal characteristics showed plasticity to the growing environment, ultimately altering growth and yield. The effectiveness of breeding efforts in western Canada has resulted in high-yielding, climate-resilient and vigorous wheat varieties over the years. Phenological observations showed modern cultivars mature earlier in terms of their compared to the founder varieties. The study of morpho-phenological and spectral indices classified studied genotypes into three distinct groups/ clusters. The selection of varieties from each group can help us obtain contrasting varieties for follow-up studies. NDVI value was markedly higher in the wet year, relative to stress environment. Yield performances and physiological traits differed to a greater extent between modern varieties and founder wheat varieties. Grain yield significantly differed among environments (p= 3.70E-106) and varieties (3.96E-19). The interaction was also significant (p=1.67E-04). Contrasting Varieties for yield traits were identified as Red Fife (Average grain yield: 2653.56 kg/ha); along with AAC Brandon (Average grain yield: 3814.12 kg/ha), AAC Viewfield (Average grain yield: 3754.98 kg/ha) on the other end. Indices (Drought tolerance index and yield stability index) based study on contrasting years showed that modern varieties like AAC Starbuck also performed best for yield traits grain yield and thousand grain weight. Weather conditions, more precisely: vapor pressure deficit (VPDleaf), majorly regulates transpiration (E_apparent). Diurnal measurements in 2021 (stress year) showed that E_apparent (transpiration rate) increased with increasing VPD leaf ~4 kPa. However, a further increase in VPD leaf (typically at 1 PM and 4 PM hours of the day) markedly decreased E_apparent, as stomata closure has occurred as an adaptive strategy. Interestingly, this closure has impacted night-time transpiration rate as well in 2021. Grain yield and thousand-grain weight (tgw) in 2022 showed positive and significant correlations with daytime E_apparent. Daytime transpiration rate showed statistically significant differences among varieties with AAC Cameron (consistent higher rate ) and AC Cadillac (consistent lower rate) shown as contrasting varieties over years (2022 and 2023). Repeated measures canopy temperature measure in 2023 for 1 PM identified Red Fife have highest temperature (29.97 0C) and AC Majestic have lower temperature (27.73 0C). Flag leaf and grain samples were also analyzed for carbon isotope discrimination, as a proxy measure of water use efficiency. Harvest showed highest carbon isotope discrimination (? %) for both flag leaves and grain samples in 2021. In 2022, AAC magnet showed highest value, but the trait was not significant for grain samples in 2022. For the residual transpiration, Carberry showed higher value constantly over years while vesper consistently showed lower values. Based on performance for stomatal traits over the years, Red Fife and Superb varieties were identified as contrasting varieties for further studies. Thousand-grain weight trait identified AAC Alida and superb (higher weight varieties) and on the other end, Neepawa and Thatcher (lower weight varieties).

In addition, Cuticular waxes coat plant aerial tissues, creating a hydrophobic barrier that mitigates water loss through the stomata. Previous experiments have investigated the flag leaf cuticular wax composition and load of Canadian wheat under control, drought and heat stress conditions, however, the genetic basis for cuticular wax responses are not well understood in these varieties. RNASeq was used to explore gene expression at key cuticular wax genes identified by prior studies was investigated using flag leaf samples of four varieties. The results indicated that the W1 locus, responsible for ?-diketone production, may be a key marker for breeding drought resistant varieties.

Extension Messages

• With the impact of climate change, older varieties are not good to grow in adverse conditions. Modern varieties are equipped with adaptive tools (stress avoidance and stress tolerance) that can minimize loss in harsh conditions.
• Wheat Breeding in western Canada has consistently played a critical role in the progress of continuous yield gain and has contributed over half of the total on-farm yield gain in the past several decades. These gains through genetic improvements should be complemented by changes in management practices, such as appropriate fertilizer use, timely weed control, and early planting in the season to utilize available soil moisture.
• Warmer temperatures caused yield loss mainly by shortening the growing season, while elevated VPD increased water loss and triggered several water stress responses. This includes reduced photosynthesis, lowered leaf area development, shortened plant height, etc.
• Breeding for climate-resilient phenotypes (such as specific spectral indices) with desirable characteristics can help to better cope with the changing climate. Adaptation strategies should be systematically examined, and the mechanisms through which they alleviate yield loss should be better understood using high throughput techniques at the farm level.
• Creating models and frameworks that can quantify yield performance in advance can be extremely useful in helping growers in future climate scenarios. Based on available data from varied environmental conditions and detailed crop tolerance/ susceptibility levels from this study, innovative models can be used to predict the performance of germplasm. Site-specific model-based analyses and recommendations of variety to growers for a specific site could be highly beneficial.
• The results indicated that the W1 locus, responsible for ?-diketone production, may be a key marker for breeding drought resistant varieties