Planting date, density, and plant establishment
Previous studies on conventional and high-oleic sunflower hybrids have revealed that planting date, between-row distance, and plant density might affect the grain and oil yield and oil composition of high-stearic and high-stearic-high-oleic sunflower crops.
Tests were carried out in a 2-year experiment (2009 and 2010) on the HSHO commercial hybrid (HS03) in Advanta’s Biotechnology Center at Balcarce in Argentina. The HSHO sunflower hybrid used in the experiment was characterized as having short stature, medium yield potential, and early medium maturity. The evaluated factors were two planting dates (22nd and 25th October and 23rd and 25th November) in 2009 and 2010, two between-row-distance treatments (0.70, 0.52 m), and three plant density levels (40,000, 65,000 and 90,000 plants per hectare).
Weather conditions benefited the growth and development of Nutrisun HSHO sunflower hybrids in 2010 compared to 2009 for both planting dates at Balcarce in Argentina. Grain yields in 2010 were double of those in 2009 (2022.1 vs. 4035.9 kg/ha, Table 1) which agrees with previous studies (Flagella et al. 2002). Rainfall was greater throughout the growing season in 2010 compared to 2009 and may explain the increased yield in 2010 as the rainfall for early planting dates in October in 2009 was inadequate. Although in 2009 rains were more abundant early and late in the season, almost no difference was observed between years in the period −10/+20 days around flowering for November planting date. The planting year and the interaction between planting year and date and their effect on grain and oil yield were significant (Table 1). Sunflower plots sown in October always had better yield than those planted in November (Table 1). Also, oil yield was greater for October planting dates and the difference among planting dates varied across years (Table 1) which was similar to what was reported by other researchers (Zheljazkov et al. 2009). The oil content proportions were 41.4 and 36.2% for October and November. The effect of early planting date on oil content derives from the most favorable conditions for incident radiation and temperature during the growing season. Oil content was observed to significantly decrease when sunflower was planted in November as well as when plant density was reduced. Seed oil content was the only variable affected by plant density (41.4, 42.5, and 42.5% for the 40, 65, and 90,000 plants/ha). Previous studies (Aguirrezabal and Pereyra 1998) showed that seed oil content remains almost constant across different plant densities whereas the other components of the kernel (i.e., hull, proteins) vary leading to changes in seed oil percentage. Seed oil composition was also affected by year and planting date. The stearic acid content was higher for early planting dates in 2009 but lower in 2010; the opposite response was true for the oleic acid content. Neither row spacing nor plant density affected the proportions of stearic or oleic acids. Although stearic and oleic acid content was affected by planting date, which might have been a consequence of different weather conditions. Studies show that genotype and weather seem to have a direct impact on oil content and fatty acid composition, and since HSHO sunflower hybrids have improved yield and oil content potential, further research to understand these interactions is needed (Cánepa et al. 2012).
Recently, sunflower hybrids differing in oil composition have been developed to provide for different industrial and human needs. France is probably the leading country for the oleic type (>75%) sunflower cultivation covering 54 and 57% of the total acreage in 2010 and 2011. The 5-year ONIDOL/TERRES INOVIA survey from 2006 to 2010 showed that the mean oleic acid content in France ranged between 85.4 and 86.7% (Labalette et al. 2012). These oils are characterized by the relative amount of saturated, mono-, and polyunsaturated fatty acids. Fatty acid composition varied depending on year, location, genotype, cultural practices, and environmental conditions (primarily temperature).
Drought and high temperatures
In the high stearic acid containing CAS-14 mutant, the stearic acid content increased with increasing temperatures. The highest stearic acid seeds were obtained from the plants that produced the seeds during the period of maximum summer temperatures (35–40 °C during the day and 20–25 °C at night) (Fernandez-Moya et al. 2002) whereas in the medium stearic containing CAS-3 and CAS-4 mutants, and a high stearic acid containing line ADV-3512, the stearic acid proportions decreased at high temperatures (Izquierdo et al. 2013). The CAS-14 mutant line has more stearic acid (37.3%) than the previous high-stearic-acid sunflower mutants like CAS-3 which had 28.8% stearic acid (Fernandez-Moya et al. 2002; Osorio et al. 1995). Due to the sensitivity of desaturases to temperature, high temperatures increase the content of mono-unsaturated fatty acids (C18:1) (Merrien et al. 2005).
An effect of temperature on the high-stearic-acid sunflower mutants was observed. Temperatures higher than 30/20 °C (day/night temperatures) were required for the expression of the phenotype of the CAS-14 mutant. Seeds from CAS-14 plants were subjected to three different high temperature treatments and seeds were collected for fatty acid half-seed analysis. As expected, the stearic acid content increased with temperature, mainly from 30/20 to 35/22 °C (14.2 and 34.0%, respectively). The maximum stearic acid (37.3%) content was obtained at 39/24 °C (Fernandez-Moya et al. 2002). A similar effect was found in the contents of the other saturated fatty acids: palmitic, arachidic, and behenic acids. Thus, a new type of temperature regulation on the stearate desaturation must be occurring.
The relationship between the growth temperature and the stearic acid content found in CAS-14 was the opposite of what was previously observed in normal sunflower oils, in which more stearic acid was produced at low temperatures (Lajara et al. 1990). In a study covering 33 field locations in Spain, it was observed that the stearic acid content decreased progressively from 6 to 3.2% from Northern Spain (colder weather) to Southern Spain (warmer weather). Also, in the medium stearic acid mutants CAS-4 and CAS-8, an inverse relationship between growth temperature and stearic acid proportions was reported. At 30/20 °C day/night temperature, these mutants had 11–12% stearic acid, whereas at 20/10 °C, they contained 18–20% stearic acid (Martínez-Force et al. 1998). In another study by Izquierdo et al. (2013) with the CAS-3 mutant, the stearic acid content at 16/16 °C was higher than at 26/26 °C (26.2 vs. 18.4%) during the grain filling period. This study also found the highest variation in the fatty acid composition in the CAS-3 mutant. This pattern was also observed in another treatment (16/16, 26/16, 26/26, and 32/26 °C) where the stearic acid content was higher for two (CAS-3 and ADV-3512) of the three high-stearic inbred lines and two (ADV-3807 and ADV-2803) of the three HSHO inbred lines at lower temperatures. A reduction of approximately 10% in the concentration of stearic acid was observed between extreme treatments (Izquierdo et al. 2013).
Nutrisun medium-stearic-high-oleic (MSHO) hybrid MS06 and HSHO hybrid (HS03) developed by the Instituto de la Grasa of Sevilla, CSIC (Superior Council of Scientific Research) in Spain and Advanta Seeds were grown in France in 2011, 2012, and 2013 and HS03 was grown at Balcarce in Argentina in 2009 and 2010 and the yields are shown in Table 1. The first Nutrisun crop was harvested in Argentina in 2008, then in Spain in 2009, and the USA in 2010.
A field experiment was conducted in 2014 in the Atlantic border region (Surgères) in France (Fig. 5). The performance of the stearic Nutrisun hybrid was the same as the other sunflower types.