Missouri researchers evaluated the genetic change and its effect on seed protein composition of soybean cultivars released during the past sixty years. They grew representative ancestral cultivars and soybean varieties derived from those germplasm lines in side-by-side plots. The results of this two-year study indicated that breeding for high yield during the past sixty years had no major influence on seed amino acid composition. The levels of amino acids in modern commercial soybean varieties were substantially similar to ancestral lines. It was interesting that the ancestral wild species, G. soja, was significantly higher in amino acids cysteine, glutamic acid, histidine and arginine and lower levels of alanine, phenylalanine, leucine and tryptophan compared to developed cultivars.
Soybean yields have been steadily improved due to plant breeding and agronomic practices, however, seed protein levels have not been increased due to the inverse relationship between yield and seed protein levels. The protein content of soybean seed appears to have been decreased over the past sixty years. The ancestral soybean cultivars contained between 38-43% seed protein compared to varieties derived from these ancestral cultivars in the 1950-1960s containing 36-41% seed protein and varieties developed in the 1980-2000s contained 36-39% seed protein.
The five ancestral lines used in this study accounts for 40% of the genetic base for all U.S. soybean cultivars and more than 56% of the Northern U.S. soybean varieties. The researchers found no variation in the genes controlling protein storage among these five ancestral lines. These results suggest that all of the ancestral lines involved in the development of modern cultivars have little or no variation in the DNA sequences of the seed storage protein genes. Even though major progress has been made in improving soybean yield, using this narrow genetic base, changes in seed protein composition has been minor.
Mahmoud, Ahmed and co-worker. 2006. Effect of six decades of selective breeding on soybean protein composition and quality: A biochemical and molecular analysis. J. Agric. Food Chem. 54(11): 3916-3922.