| Summary: | High oleic acid sunflower hybrids have been available on the market for a few years, but
research on the stability of these genotypes for oil quality traits in South African
production areas is limited. General aims of this study were to compare oil quality traits of
high oleic sunflower against traditional sunflower genotypes in different environments,
over seasons and under heat stress conditions and to identify possible genetic markers
related to the oleic acid trait that would be useful in breeding programmes.
Combined ANOVAs of oil, linoleic, oleic, palmitic and stearic acid content of 16
genotypes tested in a total of nine trials over eight locations and three seasons showed
highly significant differences between genotype, environment and GXE. Significant GXE
suggested differential response of genotypes across testing locations and years and the
need for stability analyses. Stability analyses were performed for all oil traits using
AMMI. Stability analyses indicated that high oleic genotypes 6 and 8 could be considered
stable across environments and seasons for oil and oleic acid content and genotype 9 for
palmitic and stearic acid content.
Sunflower oil quality is affected by genotype and environmental conditions with
temperature as a major influence. The effect of heat stress on seed yield and oil quality
traits was investigated by applying a maximum temperature of 36ºC to plants during the
critical seed-filling stage. This information was needed to define a breeding strategy to
further improve seed oil quality in environments where heat stress may occur. All traits
measured were significantly influenced by heat stress. The low heritability estimates
observed for seed-related yield traits indicated that genetic improvement for these traits
would be difficult. Oil and linoleic acid contents were significantly reduced by heat, while
oleic acid content was significantly increased in traditional hybrids. The oleic acid content
of the high oleic acid hybrid was unaffected, but this hybrid showed the largest decrease
in oil content. High heritability estimates observed for oleic and linoleic acid content
indicated that it is possible to genetically improve these traits under different temperature
conditions.
Since oleic acid content is influenced by the environment, this trait showed instability
across environments. Genotypic selection for this trait using linked markers is independent from the environment. A segregating population comprising 78 F2
individuals was obtained from a cross between a high oleic acid and traditional sunflower
line. AFLP and SSR markers were used to identify and map QTL, associated with the
high oleic acid trait, putatively to LG 14 of the sunflower consensus map. A major QTL
controlling the level of oleic acid was identified that explained 35% of the phenotypic
variance for this trait. Markers linked to this trait were identified that could be useful in
MAB.
Physicochemical properties and oxidative stability of seed oil of high (82.6% oleic) and
mid oleic acid (53.8% oleic) sunflower hybrids were compared with those of traditional
sunflower (65.7% linoleic and 22.9% oleic). Oxidative stability was evaluated by
measuring PV, p-AV and OSI values. High oleic acid oil had the best oxidative stability.
Since oxidative stability was related to the unsaturation level of oil, the high oleic oil with
significantly reduced linoleic acid content had the highest resistance to oxidation. Keeping
quality of commercially available vegetable oils, including high oleic sunflower oil was
evaluated using the Schaal oven test. Oil samples, placed in a heat cabinet at 63ºC were
periodically examined for keeping quality by determining PV, p-AV and RI values. High
oleic sunflower oil was twice as stable as traditional sunflower and canola oils.
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