Genetic Control of Protein and Amino Acid Content in Soybean Determined in Two Genetically Connected Populations

Soybean (Glycine max (L.) Merr.) seed protein is an important component of soybean meal for both human and animal consumption as it accounts for nearly 70% of the world vegetable protein market and is a primary source of essential amino acids for animal feed. Insufficient levels of sulfur-containing amino acids cysteine and methionine create a limiting factor for animal feed quality. An objective of soybean breeders is to find methods to increase the supply and quality of soybean seed protein. The study reported herein was conducted on two F4-derived soybean populations ('NC-Roy' x 'Prolina' and 'NC-Roy' x NC-106) segregating for total protein concentration. Phenotypic data were collected from each population in four environments for agronomic traits flowering date, maturity date, plant height, and seed yield, as well as the seed quality traits concentration of protein, oil, and eighteen amino acids. Genotypic data were collected for both populations using simple sequence repeat and single nucleotide polymorphism markers. Objectives of this study were to estimate heritability of and genetic correlations among the twenty-four traits as well as detect trait associated quantitative trait loci (QTL) via three methods: individual populations, combined population assuming four unique alleles, and combined population considering the genetically connected maternal line in both populations.;Heritability estimates obtained from these populations suggested selection for protein, oil, and certain amino acids concentration may proceed without difficulty in F4-derived lines. Significant, positive genetic correlations greater than 70% were estimated between protein concentration and all amino acids, apart from cysteine, histidine, and tryptophan. These results implied the ability to indirectly select for particular amino acids while selecting for protein concentration. Genetic correlations between protein concentration and amino acids suggested these traits are controlled by shared alleles at common quantitative trait loci; therefore, selecting alleles that confer an increase in protein concentration would likely lead to an increase in cysteine and methionine as well as the majority of the remaining amino acids.;Individual population analysis revealed regions in common across the two populations on linkage group K/9 for protein concentration. A previously reported protein concentration QTL on G/18 was also verified. Results of the combined analysis implied two protein concentration QTL, mapped to C2/6 and Z/9, were not considerably influenced by maturity date or seed yield in these populations. Given the reported information, an approach to increasing protein concentration is to backcross the regions near BARC-044639-08743 (C2/6, 36.77 cM) and Satt260 (K/9, 60.9 cM) from NC-106 into a superior inbred line.;Genomic regions on N/3, C2/6, K/9, and G/18 were significant for a majority of the amino acids. A cysteine content QTL on O/10 (88.1 -- 93.2 cM) provided and opportunity to increase cysteine content alone. However, the efficacy of this is questionable as this region was common to previously reported maturity and seed yield QTL. Cysteine and methionine QTL on K/9 and C2/6 were also associated with multiple amino acids; these regions were not specific enough for a backcrossing scheme to significantly improve the soybean seed protein quality.;Connected population QTL analysis revealed more precise regions significantly associated with protein and amino acid concentration, providing an avenue for breeders to be more effective in their attempts to increase soybean protein concentration and quality. However, results of this study suggested it may not be possible to alter the amino acid composition of protein concentration when making selections in these two populations.