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The seed oils of wild‐type sunflower (Helianthus annuus L.) germplasm typically contain 140 to 350 g kg−1 oleic acid (18:1). Sunflower germplasm with 800 to 950 g kg−1 18:1 (high oleic germplasm) has been developed with a dominant mutation (Ol) originating from the cultivar ‘Pervenets’. We speculated that this mutation reduced the activity or expression of a Δ‐12 oleate desaturase (OLD) gene. This was tested by cloning OLD genes expressed in developing seeds and comparing nucleotide sequences, OLD transcript concentrations, and OLD restriction fragment lengths among wild‐type (low oleic) and backcross‐derived mutant (high oleic) lines fixed for ol or Ol alleles, respectively. An Arabidopsis thaliana L. OLD (At OLD) cDNA probe was used to isolate a full‐length cDNA clone (OLD‐7) from a developing seed cDNA library of sunflower. OLD‐7 was strongly expressed in developing seeds, but was not expressed in the other tissues sampled. The nucleotide sequences for OLD‐7 0RFs from partially isogenic low and high oleic acid lines (HA89 and HA341) were 100% identical. High oleic lines had substantially lower OLD‐7 transcript concentrations than low oleic lines. Restriction fragment analyses showed that OLD‐7 is duplicated and rearranged in mutant lines and linked to the Ol locus; thus, increased oleic acid content seems to be caused by DNA changes affecting OLD‐7 cis regulatory sequences. OLD‐7 RFLPs distinguish between Ol locus genotypes and can be used to accelerate the development of high oleic lines in sunflower.

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