Classic Genetics and Breeding - Genetics, Genomics and Breeding of Crop Plants - page 64

2.4.2 Oil Content and Oil Quality
The highest oil content known (60 to 65%) in cultivated sunflowers is
probably close to biological limits. Oil content is determined by the plant on
which the seeds are borne. The pollen has little effect. Oil content is a highly
heritable character (Fick 1975), which can be selected on individual plants
from the early generations of a breeding program. Oil content is now
measured by nuclear magnetic resonance (NMR), a rapid, non-destructive
method, which only requires 2 or 3 g of seed. It is therefore one of the easiest
characters to select, but there is a tendency for the genotypes with the highest
oil content not to have the highest yield. This could be due to the fact that
more energy is required to produce 1 g oil than 1 g cellulose. Generally
hybrids have higher oil content than that of their parents, but this is not true
when inbred lines have 50% or more oil.
Importance of oil content depends on the economic question of whether
the seed meal has any value. In France, the character “oil yield per hectare”
is used in official trails, but farmers are not often paid for this. The genetic
gain study in 2000-2001 showed that the first hybrids had lower oil content
than the last open-pollinated variety, Peredovik, but then, in the 1980s,
there was a return to the level of Peredovik. On average, there has been no
further increase since then. There has been specialization with some varieties
showing progress for oil content, but balanced by others with improved
yield but lower oil content. The gain for oil yield per ha was 148% from 1970
to 2000 ( Table 2-1 ) .
The composition of “conventional” sunflower oil varies according to
climate: in temperate conditions, it contains up to 75% linoleic acid and
20% oleic acid, whereas in hotter climates, up to 60% oleic acid and 30%
linoleic acid is common. With no modification, this oil is valuable for direct
use and in margarine production.
A mutant which blocked the activity of the enzyme desaturating oleic
acid to linoleic acid in sunflower seed was discovered by Soldatov (1976),
with the result that proportions of fatty acids are reversed giving up to 90%
oleic acid. This character appears to be “semi-dominant” (Miller et al. 1987),
a hybrid with one oleic parent having 45-65% oleic acid and both parents
must be “high-oleic” to give a hybrid with at least 75%, the minimum level
for international designation as a “high oleic variety”. Varieties with up to
92% oleic acid have now been bred. Inheritance appears to follow the pattern
of a major gene, but some genotypes with “suppresser genes” have been
identified (Lacombe et al. 2002). Unlike oil content, which depends on mother
plant genotype, oleic acid content is determined by the genotype of the
developing seed. Therefore, high oleic crops must be grown isolated from
conventional crops and, in first generations of breeding (F 2 or backcross
populations), it is necessary to make analyses on single plants or seeds. In