A novel study of diverse genotypes (founder, eastern, and western groups) in the Canadian heritage bread wheat panel was conducted for physiological traits and yield attributes. This unique study, spanning three years (2021-2023) under rainfed conditions in Saskatoon, SK, Canada, used the Stress Tolerance Index (STI) grain yield for contrasting years to establish relationships with traits that best explain drought tolerance mechanisms.

A set of variables were identified and validated over the years, revealing that newer varieties exhibited higher drought tolerance relative to founder lines. The moderate to high broad sense heritability (h2bs) for these identified traits underscores their importance as a selection criterion. Principle component analysis (PCA) and clustering approaches were applied to identify distinct groups based on these variables. In the PCA analysis, PC1 and PC2 accounted for 39.4% and 10.8% of the total trait variation, respectively. The GYT (grain yield*trait) approach was subsequently used to calculate the superiority index (SI) based on the relationship of traits with the grain yield.

This technique effectively distinguished and ranked varieties. AAC Brandon (the most widely grown cultivar across the prairies) was associated with the maximum SI value (1.74), and Red Fife (old founder line, no longer produced) displayed the minimum value (-2.21). Groups 1 and 2 were identified as drought-tolerant genotypes, whereas Groups 3 and 5 were found to be sensitive.

The five selected varieties were further examined for trait variation, which revealed significant differences for additional physiological and yield-contributing traits. Two key ratios under drought conditions were strong indicators of drought tolerance. Higher exposed: enclosed peduncle length (Pupper:Plower) and lower Adaxial: Abaxial stomatal number during drought are features of drought tolerant variety.