Evaluation of agronomic, seed quality traits, and transcript abundance in conventional high oleic soybeans with mutant FAD2-1A and FAD2-1B genes

Two soybean omega-6 fatty acid desaturase genes [FAD2-1A and FAD2- 1B] are responsible for converting oleic acid into linoleic acid (Okuley et al., 1994). Plant introductions [PI] 603452 and 283327 have naturally occurring mutations in FAD2-1A and FAD2-1B, respectively, which hinder the conversion of oleic acid to polyunsaturated fatty acids. The end result is more functional soybean oil with exceptionally high levels of oleic acid. The homozygous alleles of FAD2-1A and FAD2-1B were combined in a BC₃F_2:4 [backcross three, second filial generation selected, advanced to the fourth filial generation] population of forty-eight lines and were evaluated in Tennessee. Each line belonged to a double homozygous genotypic class: i) double wild-type [WT] (AABB), ii) mutant FAD2-1A with WT FAD2-1B (aaBB), iii) the converse (AAbb), and iv) double mutant (aabb). All genotypic groups yielded similarly to each other and to three high yielding checks (p<0.05). When one mutant allele was present the high oleic content was increased significantly (aaBB-34.4% and AAbb-26.2%) compared to AABB-21.3%. When both mutations were combined, aabb, the mean oleic content was significantly greater (p<0.05) than all other genotypic groups (80.4%). The range of oleic acid content across all twelve double mutant groups was 77.1% - 81.8%. It appears that the high oleic genotype has a significant effect on total oil, crude protein, and the concentration of five amino acids. The aabb group had significantly more oil (240 ± 1 g kg^-1) and crude protein (400 ± 7 g kg^-1) than all other groups. This increase in crude protein is consistent with the significantly lowered amino acid concentration (p<0.05) of lysine, methionine, tryptophan, and threonine in the aabb group. Conversely, the high oleic group had the greatest concentration of cysteine (p<0.05). It appears that mutant FAD2-1 genes from PI 603452 and PI 283327 are a useful source for developing high oleic soybean lines in Tennessee with no yield drag. It will be beneficial to explore the effect of these mutant alleles on total oil and protein in the future.