Changes in seed yield and oil fatty acid composition of high oleic sunflower (Helianthus annuus L.) hybrids in relation to the sowing date and the water regime
Introduction
Sunflower is one of the most widely cultivated oil crops in the world. In 1998, the seed world production was about 28.5 million tonnes and, as edible vegetable oil, only soybean (Glicine max L. Merr.) and rapeseed canola (Brassica napus L. and Brassica campestris L.) oil production exceeded that of sunflower (FAO, 1999). Although seed oil of standard cultivated sunflower is considered to be of good quality for edible purposes, the development of cultivars with oil high in oleic acid is an important breeding objective for this crop. One advantage of this oil is its higher degree of oxidative stability than oils low in oleic acid (Fuller et al., 1967), which is desirable for frying purposes, refining and storage. From the nutritional point of view, a diet rich in monounsaturated fatty acids has been suggested to reduce cholesterol in blood plasma, in that it lowers low density lipoprotein but not high density lipoprotein (Delpanque, 2000) and, thus, the risk of coronary heart disease (Grundy, 1986).
In recent years, sunflower planted area has increased because of moderate cultivation requirements and high oil yield. Due to the sunflower ability to tolerate short periods of water deficit (Hattendorf et al., 1988, Mérrien and Grandin, 1990) the potential exists for it to become an important crop also in sub-arid environments and wherever available irrigation water is limited. In such environments, early sowing allows the crop to benefit from late winter rainfall and water can be given only as supplementary irrigation to sustain yield.
The effect of sowing dates and irrigation has been extensively studied on seed yield of standard genotypes (D'Amato and Giordano, 1992, Lanza et al., 1992, Salera, 1992, Sarno et al., 1992, Quaglietta Chiarandà and d'Andria, 1994, Dimic et al., 1996), whereas the changes in oil quality due to these agronomic practices have been poorly investigated. However, the relative proportion of single fatty acid residues is an important attribute particularly for marketing and processing. Moreover in literature data are mainly referred to standard genotypes, while very little is known on high oleic genotypes.
In particular, the fatty acid composition is known to differ between cultivars and with environmental conditions (Connor and Sadras, 1992). Genotype and temperature during oil formation exert the major effect on the proportions of oleic and linoleic acids, whereas the effect of N supply is small and depends on timing of N application (Steer and Seiler, 1990).
With regard to the effect of irrigation, Talha and Osman (1974) reported an increase in the oleic/linoleic acid ratio under water stress. On the other hand, Unger (1982) found a positive correlation between oleic acid content and water use at the vegetative stage, while Salera and Baldini (1998) observed no effect of water management on oleic acid content. When water stress occurs during the grain filling period on standard and high oleic genotypes, an increase in the oleic/linoleic acid ratio is observed with respect to more favorable water regimes in southern (Flagella et al., 2000) and northern Italy (Baldini et al., 2000).
Also the sowing date may influence fatty acid oil composition probably by modifying ontogenesis. In particular, Jones, 1984, Unger, 1986 and Cilardi et al. (1990) observed a decrease in oleic acid concentration and, conversely, an increase in linoleic acid in standard genotypes as seeding dates became later. On the other hand, Robertson and Green (1981) found that oleic acid content was intermediate for the February plantings, highest for the April planting and lowest for the late plantings.
Different sowing times and water regimes might cause different environmental conditions during grain filling and oil synthesis and also a possible alteration of the genetically programmed activation or synthesis of oleate desaturase (Connor and Sadras, 1992).
The aim of this paper was to evaluate the influence of irrigation and two sowing dates on seed yield and fatty acid composition of high oleic sunflower hybrids grown in a sub-arid environment. That in order to get deeper insight into the effects of the main agronomic techniques adopted in a Mediterranean climate on seed yield and quality of sunflower.
Section snippets
Field set up and practices
The study was conducted in 1996 and 1997 at a farm located in southern Italy (Cerignola, 15°35′ E, 41°12′ N) on a flat sandy loam soil having 1.4‰ total nitrogen content (Kjeldhal method), 22 ppm assimilable phosphorus (Olsen Method, P2O5), 745 exchangeable potassium (ammonium acetate method, K2O), 2.2% organic matter (Walchey–Black method). Two high oleic oilseed sunflower hybrids (Platon and Vyp 70, developed by the seed Company AGRA, Ravenna, Italy) were sown at two dates (on March 26 and
Results
Both yield parameters and the oil fatty acid composition showed significant differences in relation to the year, the genotype, the sowing date and the water regime (Table 1, Table 2). The more favorable rainfall regime in 1996 resulted in a better yield performance (Table 1), due to a higher number of seeds per head and 1000 achene weight, and a lower oil yield percentage. No difference in seed yield was observed between the two cultivars under study. Vyp 70 had a smaller 1000 achene weight and
Influence of year and sowing date on seed yield and quality
In 1996 yield values were higher probably due to a higher soil water content at sowing. These data are in accordance with Jones (1984) who found that higher yield and water use efficiency resulted from higher water content at sowing, especially when water stress occurred during flowering and seed filling. As regards fatty acid composition, no significant difference in oleic acid content was observed between the two years. These results confirm previous reports about the great stability in oleic
Acknowledgements
This work was partially supported by a grant from the EU POM Otris project.
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