Effect of Δ9-stearoyl-ACP-desaturase-C mutants in a high oleic background on soybean seed oil composition.

KEY MESSAGE: Two new sources of elevated seed stearic acid were identified and the feasibility of an elevated stearic acid, high oleic acid germplasm was studied. Soybean [Glycine max (L.) Merr.] oil typically contains 2-4% stearic acid. Oil with at least 20% stearic acid is desirable because of its improved baking properties and health profile. This study identifies two new sources of high stearic acid and evaluates the interaction of high stearic and oleic acid alleles. TCHM08-1087 and TCHM08-755, high stearic acid 'Holladay' mutants, were crossed to FAM94-41-3, a line containing a point mutation in a seed-specific isoform of a Δ9-stearoyl-acyl carrier protein-desaturase (SACPD-C). F2-derived lines were evaluated for fatty acid content in four field environments. Sequencing of SACPDs in TCHM08-1087 and TCHM08-755 revealed distinct deletions of at least one megabase encompassing SACPD-C in both lines. After genotyping, the additive effect for stearic acid was estimated at +1.8% for the SACPD-C point mutation and +4.1% for the SACPD-C deletions. Average stearic acid in lines homozygous for the deletions was 12.2%. A FAM94-41-3-derived line and TCHM08-1087-11, a selection from TCHM08-1087, were crossed to S09-2902-145, a line containing missense mutations in two fatty acid desaturases (FAD2-1A and FAD2-1B). F1 plants were grown in a greenhouse and individual F2 seed were genotyped and phenotyped. No interaction was observed between either FAD2-1A or FAD2-1B and any of the SACPD-C mutant alleles. Seed homozygous mutant for SACPD-C/FAD2-1A/FAD2-1B contained 12.7% stearic acid and 65.5% oleic acid while seed homozygous for the SACPD-C deletion and mutant for FAD2-1A and FAD2-1B averaged 10.4% stearic acid and 75.9% oleic acid.