Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Thomas Lübberstedt


Nitrogen (N) is a major macronutrient used in cereal production that stimulates plant growth and development. Demand for N fertilizer has been growing steadily at an annual growth rate of 1.8 percent due to the continuous increase in the cereal growing areas (mainly maize), and N is needed to maximize yield potential of agricultural crops. It has been estimated that N fertilizer used by cereals is only 33%. The rest of the applied N fertilizer is lost in the combination of surface runoff, gaseous release from soil, leaching and de-nitrification processes. In the future, for a sustainable crop production, a balance has to be maintained between maximizing yield in the available land, and using crop inputs such as N fertilizer and water in a more efficient manner.

Root growth and development is not only critical for N acquisition in plants but also to anchor the plant in the soil. Root characteristics are seldom considered as a selection criteria during breeding because of the difficulties involved in removing the entire intact root system from the soil, but they are no less important to the plant. Lines with better root architecture might help to improve N uptake and consequently plant growth particularly under N deficient conditions.

The overall goal of this project was to identify quantitative trait nucleotide, or insertion and deletion polymorphisms (SNPs / INDELs) in the candidate genes affecting root development as well as their paralogues, and test whether those polymorphisms affect genetic variation for root development and grain yield in maize under contrasting levels of N fertilization. The hypothesis of this study was, that polymorphisms in genes controlling root development in maize, or their paralogues affect variation in root morphology and consequently N uptake and NUE across a diverse set of maize inbreds. Thus, the first objective (Chapter 2) in this project was to characterize the phenotypic variation for morphological root traits at the seedling stage (6, 10, and 14 day old) in 74 maize inbred lines of an association study (AS) panel using a paper roll method. The second objective (Chapter 3) was, to evaluate the same 74 lines in the AS panel for response to contrasting levels of N by studying seedling root and shoot characteristics using a hydroponic system, and adult plant traits under field conditions. The third objective (Chapter 4) consisted of examination of nucleotide diversity at the candidate root genes, and evaluation of putative associations between SNPs within those root genes and seedling root traits measured in 6, 10 and 14 day old seedlings. The objective of chapter 5 was to use association analysis to identify SNPs associated with seedling root, and adult plant traits in maize grown under contrasting N conditions.

Copyright Owner

Bharath Kumar Thamasandra Narayana



File Format


File Size

173 pages