Resource allocation for selection of seed protein and amino acids in soybean

Soybean [Glycine max (L.) Merr.] is the one of the world's leading sources of oil and high-quality protein meal. An understanding of genotype × environment (G × E) interactions associated with crude protein (cp), and amino acids lysine (Lys), threonine (Thr), methionine (Met), and cysteine (Cys) would aid breeders in their selection efforts. The objectives of this study were to determine the impact of G × E interactions on protein and amino acid contents, to assess the optimum number of replications and environments necessary to provide a given level of discrimination among genotypes for crude protein and amino acids, and to evaluate the association of seed yield, maturity, and other agronomic traits with amino acid content. To meet these objectives, 140 F5-derived recombinant inbred lines (RILs) were developed from a cross of 'Benning' × 'Danbaekkong' and were grown in five field environments across the southern United States. The effects of genotype and G × E interaction were significant for crude protein, Lys/cp, Thr/cp, Met/cp, Cys/cp, and Met + Cys/cp (P ≤ 0.001). The genotypic variance component for crude protein was seven times larger than the G × E variance component. These two components of variance were found to be of similar magnitude for Lys/cp and Cys/cp. The G × E component of variance was slightly higher than the genotypic component for Thr/cp, Met/cp, and Met + Cys/cp. It was determined that the combination of five replications and two environments used in the present study could detect a difference of 2.5% between two genotype means for Lys/cp and Thr/cp. An increased number of plots (environment and replication combinations) would be necessary to detect a 2.5% difference or less between two genotype means for crude protein, Met/cp, Cys/cp, and Met + Cys/cp. Significant correlations were detected between yield and crude protein (r = -0.50), Lys/cp (r = 0.49), and Thr/cp (r = 0.49). Associations of crude protein and amino acids with maturity, seed weight, plant height, and lodging were negligible.