Submitted to: Maydica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2005
Publication Date: 7/24/2006
Citation: Darrigues, A., Buffard, C., Lamkey, K.R., Scott, M.P. 2006. Variability and genetic effects for tryptophan and methionine in commercial maize germplasm. Maydica. 50:147-156. Interpretive Summary: Most of the corn produced in the U.S. is used for animal feed, but it is limited nutritionally by low levels of the essential amino acids tryptophan and methionine. Breeders have used mutations to improve the levels of essential amino acids in maize germplasm, but this approach has not contributed significantly to commercial breeding programs because of the the problems associated with working with mutant germplasm. We surveyed commercial inbred lines and characterized the variation for these two compounds in these lines. We then examined the genetic control of these traits and found that it should be possible for commercial breeders to develop high tryptophan or metionine hybrids using existing commercial germplasm. This will benefit commerical corn breeders by making it easier for them to develop varieties with improved nutritional quality. Consumers and producers of meat will ultimately benefit because more nutritious corn will decrease the cost of animal feed, making meat less expensive to produce.
Technical Abstract: Maize (Zea Mays L.) is a major food and feed crop, however, maize proteins are nutritionally imbalanced due to low levels of certain essential amino acids, including tryptophan and methionine. The objectives of this study were (1)to determine the variability in methionine and tryptophan levels present in commercial maize inbred lines, (2)to characterize the genetic groups of commercial maize breeding germplasm for their methionine and tryptophan content, (3) to estimate general combining ability, specific combining ability, and reciprocal genetic effects for tryptophan and methionine content in this germplasm. Seventy-six inbred lines representing nine different genetic groups were evaluated. There was significant variability among the genetic groups and among the inbreds in some of the groups. Two six-parent diallel mating designs were completed with parents selected for low or high methionine or tryptophan levels. The analysis of the diallel crosses revealed significant general and specific combining ability effects, as well as reciprocal effects. These effects were of greater magnitude in the methionine diallel than in the tryptophan diallel. These studies suggest that methionine responds better to selection than tryptophan. Maize breeders will be able to exploit these genetic effects to develop hybrids with elevated levels of tryptophan or methionine.