UC Riverside

ABSTRACT OF THE DISSERTATION

Discovery and Verification of Quantitative Trait Loci (QTL) for Seminal Root Traits and Insights into Root to Shoot Tradeoffs in Hexaploid Wheat (Triticum aestivum L.)

by

Christopher E. Hohn

Doctor of Philosophy, Graduate Program in Plant Biology

University of California, Riverside, June 2016

Dr. Adam J. Lukaszewski, Chairperson

Wheat is among the top three cereal crops with over ca. 600 million tons being harvested annually. In terms of its range of cultivation no other crop can rival wheat. It was first cultivated over 10,000 years ago as humans shifted from hunting and gathering to settled agriculture. Since then wheat has seen more than a threefold increase in grain yield and makes up ca. 20% of the human diet. Today climate change and increased incidence of drought in areas a wheat production negatively impact grain yield. This has prompted interest in studying root system traits and how those traits may improve drought tolerance. For these reasons, the research in this dissertation was aimed at identifying quantitative trait loci (QTLs) and allelic variation for root system traits while also gaining an understanding of root and shoot relationships. To accomplish this three integrated mapping populations of bread wheat were created and sets of unique experiments were conducted. Significant variation for root system traits was observed in all three populations and QTLs were identified and verified for some of these traits. One major QTL for seminal root angle on chromosome arm 2DS was verified in two of the three mapping populations. Additionally, we were able to draw some general conclusions about the relationship between root and shoot biomass within the materials we tested. Using over ca. 6,000 data points we observed that as root biomass continues to increase beyond a certain threshold it negatively impacts grain yields and shoot biomass. However, in individual cultivars this relationship may be entirely different, with root biomass increasing proportionately to increasing grain yields without any observable threshold. When testing for allelic variation at a locus thought to control root biomass on rye chromosome arm 1RS we were unable to identify any significant differences between sources of the 1RS translocation. In a similar study testing for allelic variation for a locus on wheat chromosome arm 1BS thought to control root system plasticity in response to drought we were also unable to identify any significant difference between 1B substitution lines in a common genetic background of cv. Pavon 76.