Effects of Water Regime on Fatty Acid Accumulation and Final Fatty Acid Composition in the Oil of Standard and High Oleic Sunflower Hybrids M. BALDINI, R. GIOVANARDI, S. TAHMASEBI-ENFERADI, and G.P. VANNOZZI † Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Università di Udine, Udine, Italy Corresponding author: M. Baldini, Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Università di Udine, via delle Scienze 208, 33100 Udine, Italy. Tel.: +39 0432 558663; Fax: +39 0432 558603; E-mail: baldi- ni@dpvta.uniud.it Received: 4 June 2002. Accepted: 7 October 2002. Ital. J. Agron., 6, 2, 119-126 ABSTRACT BACKGROUND. Little has been done to study the ef- fects of agronomic factors on the fatty acid compo- sition in sunflower oil and in particular, the effect of water availability is more or less unknown. This re- search studied the effect of water availability on fat- ty acid accumulation and final fatty acid composition in the oil in high oleic and standard sunflower hy- brids. METHODS. Lysimeter trials were carried out during 1997 and 1998 to study the effects of different water regimes on fatty acid composition and accumulation in high oleic and standard sunflower hybrids. The wa- ter regimes adopted were: water table, replacement of the evapotranspiration (ET) and water stress. Two hybrids were cultivated: UD12, with a high oleic con- tent and UD87 as standard, both obtained by the Crop Production Department of Udine University. A ran- domised block design was used with four and two repli- cations, in the first and second year, respectively, and the main yield characteristics were evaluated at matu- rity. Achene samples were collected, every 6 days, from last anthesis until maturity in order to study achene dry weight, oil and fatty acids accumulation. RESULTS. In the standard and high oleic hybrids the fatty acid composition stabilised between the 17 th and 23 rd day after the end of flowering and in the stan- dard hybrid the ratio between oleic and linoleic fat- ty acids reached a value very close to one. Water stress significantly increased oleic acid content (of ap- prox. 5%) with respect to the other water regimes in the high oleic hybrids during both years, reducing the dry matter and oil accumulation phases, with all the enzyme activities involved, including ∆-12 desaturase, which is responsible for the desaturation from oleic to linoleic acid. CONCLUSION. Water stress, causing accelerated and earlier embryo development and lipid accumulation therefore determines a shorter duration of all enzy- matic activities, including those of ∆-12 desaturase and this could reflect on the final acid composition. This hypothesis could also explain some inconsistent qualitative results of the high oleic hybrids obtained in different years and environments. INTRODUCTION The nutritional quality of sunflower oil is due to the high percentage of C:18 fatty acids, in par- ticular linoleic (18:2) and oleic acid (18:1), which together represent about 90% of the fatty acid total, with the remainder being made up of palmitic (C16:0) and stearic acid (C18:0). From 1977 onwards, after the FAO published results on the possible negative effects of some fats and oils on human health, interest in polyunsaturat- ed fatty acids of plant origin grew and there have been many studies done to determine the effect on health of the different fatty acids in the diet. In general a diet rich in vegetable oils prevents heart disease (Krajcovicova- Kudlako- va et al., 1997). In particular, a diet rich in mono-unsaturated fatty acids reduces the cho- lesterol level associated with low-density lipoproteins (“harmful cholesterol”) and has no effect on the level of the triglycerides or on the cholesterol associated with high density lipopro- tein, if compared to a diet rich in saturated fat- ty acids (Grundy, 1986). Other more recent studies have reached the same conclusion: a di- et intended to prevent cardiovascular disease must include a reduction in saturated fatty acids intake (Jing et al., 1997) and these should not provide more than 30% of the energy supplied by fats (Woo et al., 1997). † The work can be attributed in equal parts to the authors M. Baldini, R. Giovanardi and G.P. Vannozzi. S. Tahmasebi- Enfradi was responsible for the section on chemical analyses.