Soybean [Glycine max (L.) Merr.] genotypes with increased beta-conglycinin (BC) and reduced glycinin (Gly) may be beneficial to food product quality and to human health. A soybean line, B2G2, developed in Japan, has the recessive alleles gy1, gy2, gy3, gy4, and gy5 that control Gly content. Its seed protein has about 50 g kg-1 BC and 0 g kg-1 Gly. Monsanto Co. has used B2G2 to develop lines with different combinations of recessive and wild-type alleles at the five Gy loci. The first objective of this research was to determine the influence of different combinations of the gy and Gy alleles on the content of Gly and BC and their impact on agronomic traits. The protein content, oil content, protein composition, yield, and maturity of 19 lines in each of eight genotypic classes representing different gy allele combinations were compared in five populations. The BC content was greatest for lines with gy1,2, gy4, and gy5 and for lines with the five gy alleles. Mean grain yield was significantly different among the eight genotypic classes; however, the differences were not consistent among populations. It should be possible to develop lines with gy alleles that have increased BC, reduced Gly, and similar protein content, oil content, yield, and maturity compared to lines with Gy alleles.

The second objective of this research was to determine the effect of locations and planting dates on protein composition in lines with different combinations of gy and Gy alleles. Planting dates did not significantly affect protein composition, but the means of locations were significantly different for all of the protein components, except for the A124 subunit of Gly. Grain produced at different locations would be expected to differ in BC content, but planting dates would not be expected to significantly affect that protein component.

The third objective of this research was to determine if DNA markers located on the same linkage group as the genes controlling the  subunit of BC were associated with a reduction in the  subunit and an increase in the ′ subunit content. The protein composition of seven genotypes with cytosine (C) nucleotides at two closely linked marker loci (CC-CC) and seven genotypes with thymine (T) and adenine (A) nucleotides at the same marker loci (TT-AA) were compared. The  subunit content of the CC-CC genotypes was significantly lower by 3.1 g kg-1, and all CC-CC genotypes had an ′ ratio of < 1.0. In two populations developed by crossing a CC-CC parent with a TT-AA parent, the marker genotype was associated with the ′ ratio. There were 7 % of the TT-AA plants and 33 % of the CC-CC plants that had an ′ ratio of < 1.0. These two markers should be useful in selecting for the desired ′ ratio, but it may be possible to develop markers that are more predictive.