Elucidation of genetic targets and high throughput phenotyping methods for improvements to crop sustainability

Twohey III, Robert J

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https://hdl.handle.net/2142/130135 Copy

Description

Title

Elucidation of genetic targets and high throughput phenotyping methods for improvements to crop sustainability

Author(s)

Twohey III, Robert J

Issue Date

2025-07-16

Director of Research (if dissertation) or Advisor (if thesis)

Studer, Anthony J

Doctoral Committee Chair(s)

Studer, Anthony J

Committee Member(s)

• Cousins, Asaph B
• Jamann, Tiffany M
• Leakey, Andrew DB

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Zea mays
• water use efficiency
• stable carbon isotopes
• Vapor Pressure Deficit
• stomata, transpiration, specific leaf area

Abstract

As climate change causes sporadic rainfall patterns and increased drought, there is a greater need to develop new Zea mays lines with improved water use efficiency. Identifying genetic targets and improving our understanding of the mechanisms driving variation within individual traits will provide the opportunity to breed crops for increased water use efficiency. This dissertation investigates a subset of component traits related to water use efficiency and aims to improve our understanding of the variation present within traits related to water use efficiency and use quantitative genetic approaches as an attempt to identify genetic targets that will allow for the future development of climate resilient crops. First, a Z. mays line with a highly negative carbon isotope signature was used to develop a biparental mapping population to identify a single large effect QTL. Further investigation revealed a large deletion in the carbonic anhydrase 1 gene. This mutation led to a decoupling of carbon isotope signature and intrinsic water use efficiency suggesting a better understanding of this relationship is necessary before carbon isotope signatures can be used as a proxy measurement of intrinsic water use efficiency in C4 species. Next, a slac1-2 mutant hybrid with stomata that were always open was grown across multiple field environments for physiological and agronomic characterization. The relationship between stomatal conductance, photosynthesis, and yield was dissected and provides evidence to support an opportunity to improve intrinsic water use efficiency with further reductions in stomatal conductance while maintaining photosynthetic productivity. Wild-type Z. mays hybrids did not show any photosynthetic or yield reduction due to decreased stomatal conductance when compared to the slac1-2 open stomata phenotype hybrid. Next, a new high throughput phenotyping protocol measuring limited transpiration response to increasing vapor pressure deficit was developed and tested. Significant variation was observed in stomatal response and vapor pressure deficit sensitivity traits when gas exchange was collected from the Nested Association Mapping Founders under high vapor pressure deficit. Chamber and field measurements of transpiration response under increased vapor pressure deficit were compared and while vapor pressure deficit breakpoints were seen in both environments, differences were observed in the rate of stomatal response and vapor pressure deficit sensitivity. Finally, a large QTL associated with specific leaf area was identified in two Nested Association Mapping Recombinant Inbred Line populations. Further investigation of the QTL interval was unsuccessful in identifying a refined interval or candidate genes; however, this work provides a new genomic target for future studies. These objectives describe the use of genetic variation within several water use efficiency component traits combined with leveraging new screening protocols and genetic tools to improve our understanding of the mechanisms controlling water use efficiency in Z. mays. The findings described in this dissertation can act as a foundation for future studies leading to lines with improved sustainability traits.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/130135

Copyright and License Information

© 2025 Robert J. Twohey III

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