Oil Composition Variations - Genetics, Genomics and Breeding of Crop Plants - page 276

(C18:3) have been developed for different end uses through conventional
breeding. When the necessary genetic variation is not available within
Brassica species, gene transfer by genetic transformation has been applied,
as this approach is not restricted by the sexual incompatibility barrier across
species. The fatty acids targeted by the transgenic approach included fatty
acids with various carbon chain lengths ranging from C8 to C22, with
different numbers of double bonds, and with various functional groups
such as epoxy and hydroxy fatty acids. A commercial specialty oil with
high level of a novel fatty acid, lauric acid (C12:0) was produced as a result
of the transfer of a FatB thioesterase gene from a distantly related plant species
that produces seed oil with high level of this unusual fatty acid. Considerable
progress has been achieved in altering the relative levels of the fatty acids
found in Brassica oils for increased health and economic benefits and in
developing Brassica oils, which contain other unusual fatty acids, mainly
through genetic transformation. Although the use of natural or induced
mutations in the fatty acid biosynthesis within Brassica remains a valid
option for oil modification, the transgenic approach will play an increasingly
important role in the development of Brassica oils with altered novel fatty
acid composition.
8.2.4.2 Linoleic and Linolenic Acids in Sunflower
In sunflower, as in most Asteraceae seed oils ( Carthamus , Vernonia ,) linolenic
acid exists as a trace. Since it is a common feature to the whole taxon, this
suggests that this function has been lost when the Asteraceae merged. In
contrast, the whole plant tissues display common linolenic acid content in
membranes and leaf tissues. The FAD3 enzyme is, therefore, not expressed
in the seed whereas it is highly expressed in other tissue. Since some
programs would seek to enhance linolenic acid content in sunflower, the
underlying mechanism has to be unravelled to start these programs.
In high-oleic sunflower some RILs display a very low oleic level
(10-12%) but at this moment we do not know if the trait is heritable to breed
high-linoleic sunflower (Lacombe et al. 2002). Another interesting feature is
the mid-oleic level of RIL families that did not carry the Pervenets mutation.
Up to now, we have no explanation for such a high level of oleic acid content
in traditional sunflower.
8.2.5 Wild Annual Sunflowers for Improving Oil Content and
Quality in Cultivated Sunflower
We have shown through this review that sunflower oil has the potential to
be improved for nutritional and industrial purposes through selection and
breeding. The diversity in cultivated sunflower has been broadened by