Identification and Screening of Traits Affecting Plant Water Use Efficiency

Thomas martin Sexton

Amidst growing global populations and food demand, increases in crop yields are plateauing as traits under strong selection reach maximums or are optimized. This creates a need to target novel physiological traits for improvement. Whole plant water use efficiency (WUEplant) is a crucial component of crop performance under water-limited conditions, but is a complex trait affected by many physiological processes and environmental interactions. In order to select for enhanced performance in breeding and crop improvement programs, high throughput screening for WUEplant or its components is necessary and requires a better understanding of the physiological variation driving changes in WUEplant. This dissertation focuses on identifying and screening variation in physiological traits affecting WUEplant. Carbon isotope discrimination, visible and thermal imaging, and hyperspectral reflectance were used as high throughput tools to detect differences in WUEplant at the plant and leaf level. Hyperspectral reflectance was used for rapid estimates of maximum photosynthetic carboxylation capacity that drive WUEplant. We show that increases in screening accuracy can be achieved by limiting spectral data included for model development. Reducing reflectance data also allowed for the identification of specific reflectance wavelengths related to carboxylation capacity, a key component of building robust models. Water use traits that drive WUEplant were identified in two separate experiments, using spring wheat cultivars where greater WUEplant was associated with biomass accumulation. These differences in WUEplant were able to be identified with thermal imaging and carbon isotope discrimination. Increased biomass accumulation resulted from lower leaf temperatures that reduced evaporative demand on leaves allowing greater stomatal conductance and carbon fixation without increased water loss. Additionally, increased rates of water use and growth immediately following drought onset allowed for greater WUEplant. In summary, the research presented here quantified the effects of traits regulating water use and carbon gain on crop performance under water limited conditions and improved mechanistic understanding of how high throughput measurements of reflectance relate to photosynthetic capacity. This dissertation advances existing efforts to develop effective screening methods of crop genotypes for enhanced physiological performance and yield under water-limited conditions.

Identification and Screening of Traits Affecting Plant Water Use Efficiency

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