Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: GENETIC ANALYSIS OF SELECTION RESPONSE IN MAIZE POPULATIONS
2009 Annual Report


1a.Objectives (from AD-416)
Our overall goal is to determine the genetic foundation for morphological and compositional characteristics that enhance agronomic performance and quality of maize grain and stover. We will also develop new tools for measuring economically important traits in maize. For the next five-year research cycle we will:

Objective 1: Identify key morphological phenotypes and the underlying genes and/or genetic systems that have contributed to improvement in grain yield and other important agronomic phenotypes in maize. Objective 2: Develop new tools for evaluating and identifying maize varieties with superior properties for bioenergy production. Objective 3: Identify key physiological and biochemical phenotypes and the underlying genetic systems that have contributed to improvement in methionine content and bioenergy potential.


1b.Approach (from AD-416)
Objective 1: We will map genomic regions and attempt to identify candidate genes for morphological phenotypes that may have changed in response to selection for agronomic performance in the Iowa Stiff Stalk Synthetic population. We will focus on three morphological phenotypes, silking-anthesis interval, leaf angle, and number of ears per plant. We will determine the magnitude of selection response for these traits in Iowa Stiff Stalk Synthetic population and determine if any of these are correlated to agronomic traits in the base population. We will then use advanced cycles of selection and the base population to generate a genetic mapping experiment to determine how many regions and what magnitude of effects those regions have for the morphological traits. We will use all of the information collected to determine if response to selection for agronomic traits can be explained by indirect response for morphological characters. Objective 2: One method of production of biofuel from plant material involves fermentation, which is dependant on the production of sugars from the plant material. We will develop methods for screening varieties for their ability to produce sugars in small scale processes that mimic current methods being used for production of ethanol. Sugars will be quantified using bacterial biosensor strains we will develop using bacterial genes known to respond to sugar levels. Objective 3: We will characterize the genetic mechanism controlling production of methionine by biochemical analysis of populations selected for high and low methionine. In addition, we will determine if different genetic mechanisms controlling methionine levels are complimentary by combining them genetically and determining the methionine levels in the different genetic combinations.


3.Progress Report
We evaluated the content of the essential nutrients methionine, tryptophan, and lysine in maize germplasm in order to identify varieties with high nutritional value that can be used in breeding programs aimed at improving nutritional quality. Germplasm was also evaluated for its suitability for production of ethanol. Breeding populations were advanced and analyzed genetically and biochemically to characterize the genetic mechanisms controlling nutritional quality. In order to better understand the genetic control of grain yield, populations were developed that will allow identification of morphological traits that have changed in the course of selection for agronomic performance. These traits are likely to be yield determinants and understanding their genetic control will allow breeders to improve grain yield more rapidly.


4.Accomplishments
1. Developed maize varieties with improved amino acid balance. Animal feed is the greatest expense for meat producers in the US. While grain crops such as corn provide an inexpensive base for animal feed, their nutritional value is limited by their amino acid content. Expensive amino acid supplements are required to create diets with optimal nutritional value for animals. These supplements increase the cost of animal feed. We characterized transgenic corn and determined that the content of the limiting amino acid lysine in grain was increased by 40%. In addition, we used traditional breeding approaches to alter the level of the limiting amino acid methionine. High and low methionine populations differed in methionine content by 19% after three cycles of selection and high methionine grain performed better in an animal feeding trial. These successes establish the feasibility of the approaches we used, and facilitate the development of commercial corn with improved nutritional value. Application of this technology will result in a reduction in the cost of food production.

2. Genetic analysis and mapping of grain quality traits. Low levels of the essential amino acids lysine, methionine and tryptophan limit the value of corn grain for animal feed and as a staple in human diets. Increasing the levels of these compounds through breeding is an attractive approach that would be facilitated by a better understanding of genes controlling the levels of these traits. Using an approach called Qualitative Trait Loci (QTL) mapping, we identified several genetic loci that control the levels of these amino acids and other grain quality traits. Knowing the genetic location of these genes will facilitate breeding efforts to improve these traits, leading to maize with improved nutritional value.


5.Significant Activities that Support Special Target Populations
Organic poultry producers require maize grain with elevated levels of methionine because methionine supplements may be banned from organic poultry diets soon. We provided high methionine germplasm to the Michael Fields Agricultural Institute to facilitate their efforts to develop high methionine grain.


Review Publications
Bicar, E.H., Woodman-Clikeman, W., Sangtong, V., Peterson, J., Lee, M., Scott, M.P. 2007. Production of Transgenic Maize with Improved Amino Acid Balance Containing a Milk Protein in Grain. Transgenic Research. 11:11-20.

Gutierrez-Rojas, A., Scott, M.P., Leyva, O.R., Menz, M., Betran, J. 2008. Phenotypic Characterization of Quality Protein Maize (QPM) Endosperm Modification and Amino Acid Contents in a Segregating Recombinant Inbred Population. Crop Science. 48:1714-1722.

Haney, L.J., Lamkey, K.R., Kirkpatrick, K., Coors, J.G., Lorenz, A.J., Raman, D.R., Anex, R.P., Scott, M.P. 2008. Development of a Fluorescence-based Method for Monitoring Glucose Catabolism and its Potential use in a Biomass Hydrolysis Assay. Biotechnology for Biofuels. 1:17.

Scott, M.P., Darrigues, A., Stahly, T., Lamkey, K. 2008. Recurrent Selection to Control Grain Methionine Content and Improve Nutritional Value of Maize. Crop Science. 48:1705-1713.

Edwards, J.W. 2008. Predicted Genetic Gain and Inbreeding Depression with General Inbreeding Levels in Selection Candidates and Offspring. Crop Science. 48:2086-2096.

Wardyn, B.M., Edwards, J.W., Lamkey, K.R. 2009. Predicted Gains from Inbred-Progeny Selection Is Inferior to Half-sib Selection for Two Maize Populations. Crop Science. 49:443-450.

Sheperd, C.T., Scott, M.P. 2009. Construction and Evaluation of a Maize Chimeric Promoter with Activity in Kernel Endosperm and Embryo. Biotech and Applied Biochemistry. 52:233-243.

Last Modified: 12/19/2014
Footer Content Back to Top of Page