Abstract
The effects of water deficit conditions on the qualitative and quantitative characteristics of sunflower seed and seed oils were assessed. Two sunflower cultivars (Gulshan-98 and Suncross) were sown in the field. The water stress treatment was applied at the vegetative or the reproductive stage. Analysis of the sunflower seed showed that the oil content decreased (a decline of 10.52% relative to the control) significantly (p ≤ 0.05) due to water stress when imposed at either of the growth stages. Both of the sunflower cultivars studied showed differential responses to water stress with respect to oil oleic and linoleic acid contents. A significant negative correlation in oil oleic and linoleic acid was observed in cv. Gulshan-98 under water deficit conditions as compared to Suncross in which no such effect of water stress on oleic and linoleic acid was observed. Water deficit conditions caused a reduction in linolenic acid in Gulshan-98, whereas it remained unaffected in Suncross. The stearic acid content increased in cv. Gulshan-98 due to drought, whereas no effect due to water stress was observed on oil palmitic acid content in either sunflower cultivar. Overall, oil unsaturated fatty acids remained unchanged in the drought stressed or normally irrigated plants of both cultivars but saturated fatty acid increased in Gulshan-98. Individual (α, γ, and δ) and total tocopherol contents in the seed oil increased significantly with the application of water stress in both cultivars. An assessment of the physical and chemical characteristics of the oils of both sunflower cultivars revealed that drought stress caused a marked increase in the content of un-saponifiable matter (18.75% with respect to the control) and a decrease in iodine value (5.87% with respect to the control), but saponifcation value, density, specific gravity and refractive index remained unchanged.
Highlights
The vital role of the sunflower crop depends mainly on the characteristics of the oil produced, which can be used directly or after processing in food and non-food industries (Vermeercsh, 1996)
An analysis of variance showed that drought stress imposed at different growth stages had no significant effect on oil palmitic acid content; oil stearic acid content increased significantly due to the imposition of water stress at different growth stages and this effect was observed only in cv
This maximum increase in oil stearic acid content was observed when water stress was applied at the reproductive stage
Summary
The vital role of the sunflower crop depends mainly on the characteristics of the oil produced, which can be used directly or after processing in food and non-food industries (Vermeercsh, 1996). Sunflower oil contains four important fatty acids, namely palmitic (16:0), stearic (18:0), oleic (18:1), and linoleic (18:2) acids (Baydar and Erbas, 2005). One potential reason for variability in oleic acid content may be water stress soon after the initiation of flowering (Monotti, 2003). It is known that genetic and environmental factors play an important role in the economic outcome of an oilseed crop and can affect the oil QASIM ALI, MUHAMMAD ASHRAF AND FAROOQ ANWAR yield and quality of its grain/seed production. Lack of water during all stages of growth and development is one of the limiting factors for seed growth and can influence the composition of its oil (Flagella et al, 2002). According to a number of reports, it is evident that the stress tolerance of most plant species varies at different growth stages (Kefale and Ranamukhaarachchi, 2006; Li-Ping et al, 2006; Nam et al, 2001)
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