Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2007
Publication Date: 9/23/2008
Citation: 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. Interpretive Summary: One of the main nutritional limitations of corn is it's content of the essential amino acids lysine trypothpan and methionine. A consequence of this limitation to meat producers is that they have to supplement animal feed with expensive sources of these amino acids. Genetic improvements to maize can be made to increase the levels of these limiting nutrients. One approach to doing this is with the mutation opaque2 (o2). This mutation increases the nutritional value of corn, but decreases grain qulaity. In order to breed for improved corn containing the o2 mutation, it is necessary to understand the relationship between nutritional quality, grain quality and the environment. In this paper, we characterized these relationships using a collection of o2 maize lines and evaluating their amino acid content and grain quality traits in several environments. We observed negative correlations between amino acid content and most grain quality triats. This information will allow breeders to design more efficient selection protocols that will reduce the time required to develop lines with improved nutritional quality. The ultimate impact of this work will be to decrease the cost of meat production.
Technical Abstract: The protein quality of maize can be improved by replacing normal Opaque2 alleles with non-functional recessive alleles (o2). Homozygous o2 kernels have increased levels of lysine and tryptophan. Unfortunately, the associated soft texture of the o2 kernels causes poor yield and susceptibility to diseases and insects. Breeding programs have restored the desirable ratio of hard vs. soft endosperm in o2 genotypes developing modified endosperm versions called Quality Protein Maize (QPM). QPM germplasm, developed mostly by the International Maize and Wheat Improvement Center, is currently utilized in breeding programs worldwide and has been demonstrated to be competitive in yield trials when compared to local checks. To contribute to an increased understanding of the genetics of endosperm modification, a population of 146 recombinant inbred lines (S5 to S7) derived from a cross between the o2 inbred line B73o2 and the QPM inbred line CML161 was evaluated in two Texas locations from 2004 to 2006. Four traits related to endosperm texture showed significant effect of the inbred lines, high heritability estimates (h2 = 0.83- 0.94) and high genetic correlations (GC) among them (GC= 0.81-1.0). Relative content of the essential amino acids lysine, tryptophan and methionine also showed significant effects of the lines, genetic correlations GC = 0.63-0.68, and heritabilities h2 = 0.71-0.80. Negative correlation was observed between endosperm texture traits and amino acid content. Nevertheless, favorable responses to selection would be expected for both traits if selection strategies include monitoring of both endosperm texture modification and relative content of the essential amino acids.