Date of Award

Spring 2015

Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Mitchell R. Tuinstra

Committee Chair

Mitchell R. Tuinstra

Committee Member 1

Tobert R. Rocheford

Committee Member 2

Tony J. Vyn

Committee Member 3

David Rhodes

Committee Member 4

Patrick J. Brown


Genetic Analysis of Nitrogen Remobilization and Kernel Composition in Zea Mays L. and Sorghum Bicolor (L.) Moench. Major Professor: Mitchell Tuinstra. Modern maize (Zea mays L.) production relies heavily on nitrogen fertilization for high productivity. Over-application of nitrogen fertilizers in cropping systems can have detrimental economic and environmental effects. For this reason, improving Nitrogen Use Efficiency (NUE) is a major goal of breeders and producers. Nitrogen Utilization Efficiency (NUtE) is one component of NUE, and the most important component under N-limited conditions. In this study we examined the genetic controls of the timing and preferential canopy position of leaf N remobilization during reproductive growth stages. Utilizing a diversity panel of over 2,400 lines, genome wide association mapping was conducted in 2012 and 2013 to examine leaf chlorophyll content at different growth stages and kernel composition at maturity. Chlorophyll content meters were utilized for measurements of leaf chlorophyll content on two different leaves at VT, R2, and R4 sampling times. Near infrared reflectance spectroscopy (NIRS) was utilized for analysis of kernel composition on whole kernels. NIRS was also utilized for analysis of kernel composition on whole kernels of sorghum (Sorghum bicolor L. Moench) in a diverse panel of 840 accessions; with the goal of applying known genetic controls of maize kernel composition to gain a greater understanding of the controls of sorghum grain composition. Results from the maize leaf chlorophyll analysis and sorghum kernel composition analysis suggest a role for NADH - Glutamate Synthase as a sink control of N remobilization from the leaves. Genes identified in these analyses suggest that genetic controls at both the source and sink level affect the timing and rate of N remobilization from the leaves. Knowledge of these genetic controls may be utilized in breeding programs to select lines with improved NUE and NUtE characteristics.