Reduced palmitate content in soybean [Glycine max (L.) Merr.] is controlled by two major alleles, fap1 and fap3. This study was conducted to determine the role that modifying genes may have on the reduced palmitate trait in lines homozygous for the major alleles. Two lines homozygous for fap1 and fap3, AX5152-34 and AX5152-105, were each crossed as donor parents to a high-yielding cultivar with normal palmitate, 'Kenwood' or 'Marcus'. The F1 plants were back-crossed to the high-yielding cultivar. Two experiments were grown in randomized complete-block designs at three locations in Iowa with two replications per location. The Kenwood experiment consisted of 14 F4:6 lines from the cross AX5152-105 x Kenwood, 83 BC1F3:5 lines from five BC1 families from the backcross Kenwood x (AX5152-105 x Kenwood), Kenwood and AX5152-105. The Marcus experiment contained 14 F4:6 lines from the cross AX5152-34 x Marcus, 69 BC1F3:5 lines from the backcross Marcus x (AX5152-34 x Marcus) among six backcross families, Marcus and AX5152-34. All lines, except Kenwood and Marcus, were homozygous for both fap1 and fap3. The influence of modifying genes on palmitate content was evident in both experiments. There were significant differences in palmitate content among single-cross lines, among backcross lines, and among lines within individual backcross families. The palmitate content of each donor parent was significantly different from the means of the corresponding single-cross and backcross populations. Lines with reduced palmitate were obtained that had higher yield than the recurrent parents, which indicated that reduced palmitate is not detrimental to yield. Lines with reduced palmitate generally had reduced oil content.
