Effect of saline water on oil yield and quality of a high oleic sunflower (Helianthus annuus L.) hybrid

Sunflower is a species moderately tolerant to salt stress and is currently cultivated in dry areas where salinity can be a threat. The effect of salt stress on achene yield has been investigated, but no information exists about its effect on the oil fatty acid composition. The aim of this paper was to evaluate the changes in oil yield and fatty acid composition in a high oleic hybrid submitted to different salinity levels of irrigation water. Furthermore, since the addition of a leaching fraction to the irrigation volume may be relevant to prevent excessive soil salinization, a water regime equal to 1.5 maximum evapotranspiration (1.5 ETc) was compared with the restoration of evapotranspiration (1 ETc). A pot experiment was carried out in a greenhouse with a high oleic sunflower hybrid (Platon) grown on a loam soil under two irrigation regimes with five salinity levels of irrigation water (0.6, 3, 6, 9 and 12 dSm−1). At harvesting, seed production, oil yield and fatty acid composition were determined. The percent seed yield decrease per unit increase of irrigation water electrical conductivity (ECw) was higher for 1 ETc (7%) than for 1.5 ETc (5.8%). Oil yield showed a significant decrease from 38.3 to 3.4 g per head on increasing salt stress and a marked increase of about 50% with the higher irrigation volume. Under our experimental conditions with a medium textured soil, this result confirms the importance of leaching to limit salt accumulation along the soil profile, thus reducing seed and oil yield drop under salt stress. Concerning fatty acid oil composition, under all the adopted experimental conditions, both oleic and linoleic acid accounted together for 90% of total fatty acid concentration, while stearic and palmitic acid were about 4%. No great differences were observed in fatty acid composition between the two irrigation regimes. With the higher irrigation volume, only a slight decrease in linoleic and gadoleic acid and an increase in arachidic acid were observed. The only significant differences among saline treatments were observed for oleic and linoleic acid. Oleic acid showed an increase from 82.8% in the control to 86.8% at the highest salinity treatment. Inversely, for linoleic acid a progressive decrease from 6.9 to 2.8% with increasing salinity level was observed. These results will be discussed in the light of a possible inhibition of oleate desaturase occurring under salt stress