QTL mapping and optimum resource allocation for enhancing amino acid content in soybean
Warrington, Caleb Van
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Soybean [Glycine max (L.) Merr.] is the world’s leading oilseed crop and provider of high quality protein meal. The protein portion of the soybean seed represents an energy-efficient source of amino acids for use in animal diets. As a sole dietary source of protein for poultry and swine, soybean is deficient in the sulfur-containing amino acids methionine (Met), cysteine (Cys), and may also have sub-optimum levels of threonine (Thr), and lysine (Lys). Enhancing these essential amino acids would improve the nutritive value of soybean meal and provide additional value to the animal feed industry. In this study, a population of recombinant inbred lines (RILs) from the cross of ‘Benning’ × ‘Danbaekkong’ was used to investigate the inheritance of quantitative trait loci (QTL) associated with protein and amino acid concentrations and the presence and magnitude of genotype × environment interaction for these traits. The RILs were grown in five field environments. QTL were detected for crude protein (cp), Lys/cp, Thr/cp, Met/cp, Cys/cp, and Met+Cys/cp using DNA markers. The Danbaekkong allele at a major protein QTL was found to be associated with reduced levels of each of the amino acids. Selection for amino acid QTL on other chromosomes may increase protein quality and retain a high level of overall crude protein. The effect of genotype × environment was relatively minor for each trait based on an assessment of the variance components. The estimated the number of environments and replications necessary to detect certain differences between two genotype means was determined. Results indicated that five replications and two environments could detect a difference of 2.5% between two RIL means for Lys and Thr. An increased number of plots (environment/replication combinations) would be necessary to detect a 2.5% difference or less between two RIL means for crude protein, Met/cp, Cys/cp, and Met+Cys/cp. This information would be useful in developing the most cost-effective and efficient testing scheme for these traits in a breeding program for these traits. This research should increase the understanding of the genetic basis for protein and specific amino acids and provide for effective and efficient genetic improvements for these traits.