Bread Wheat Genotypes Accumulating Free Proline and Phenolics Can Better Tolerate Drought Stress Through Sustained Rate of Photosynthesis

Drought poses a severe threat to global wheat production and world food security. This study was conducted to evaluate bread wheat genotypes for drought tolerance based on different morphological, biochemical, and physiological traits. The responses of 25 bread wheat genotypes of Pakistani origin were evaluated based on morphological, biochemical, and physiological traits under optimal (70% water holding capacity (WHC)) and drought stress (35% WHC) conditions. Sufficient genotypic variability was noted in the tested genotypes on the morphological (shoot length, relative leaf water contents, and seedling dry weight), biochemical (membrane injury index, leaf free proline, and total soluble phenolic contents), and physiological traits (chlorophyll meter value, intercellular CO2 concentration (Ci), stomatal conductance (gs), photosynthetic rate (A), ratio of photosynthetic rate and intercellular CO2 concentration (A/Ci), transpiration rate (T), and instantaneous water use efficiency (WUEins)) under both control and drought stress conditions. The principal component analysis (PCA) under drought stress showed 78.3% variability of morpho-biochemical traits and 67.0% of physiological traits. Bi-plot of PCA showed the genotypes SQU-2, SQU-4, SQU-10, and SQU-11 are tolerant under drought stress and grouped based on high A, and A/Ci. Similarly, the genotypes SQU-8, SQU-9, SQU-14, SQU-15, SQU-16, and SQU-24 were also tolerant and grouped based on high WUEins and Ci under drought stress. In conclusion, significant genotypic variability was found among the tested wheat genotypes based on morphological, biochemical, and physiological traits, which can be used in future breeding programs to develop drought-tolerant bread wheat genotypes. The genotypes SQU-9, SQU-10, SQU-7, and SQU-13 had better growth under drought stress than other genotypes due to the accumulation of free proline and soluble phenolics which helped maintain tissue water status and sustained the photosynthesis.