Agronomic approaches in yield and quality stability of high oleic sunfl owers (<em>Helianthus annuus</em> L.)

Abstract

Sunflower (Helianthus annuus L.) is, together with soybean, rapeseed and peanut, one of the most important annual crops in the world grown for edible oil. Regular sunflower oil is characterized by its high content of the essential linoleic acid (C18:2). The high oleic (HO) sunflower oil is in appearance very similar to regular sunflower oil. However, the fatty acid profile differs quite dramatically from the regular type. The HO sunflower oil contains over 80 % oleic acid (C18:1), whereas the regular sunflower oils oleic acid content stays around 20 %. The high oleic sunflower has a high potential for industrial use such as oleo chemistry, bio lubricants or bio diesel. Oil from recent high oleic sunflower varieties contains up to 90 % oleic acid and more. Although the HO sunflower has a yield potential comparable to the conventional sunflowers, there are certain constraints that hinder its production in Germany. Cold and wet weather conditions affect sunflower’s potential during the period of seedling establishment as well as the harvest. Fungal diseases especially Sclerotinia sclerotiorum (white rot) and Botrytis cinerea (grey mould) are prevalent. Therefore it is essential to explore and test alternative agricultural approaches that ensure stable kernel and oil yield, desired oil composition, and promote healthy plant development in the predominantly wet autumn, since HO sunflowers mature late under central European climatic conditions. Three different HO sunflower varieties representing different ripening classes were examined for yield, quality and fungal disease rate at two different locations, Braunschweig and Eckartsweier, representing two different climatic regions in central
Europe. Following approaches were tested in this study: Since there is no registered fungicide for sunflowers in Germany, a broad spectrum fungicide Folicur, which is predominantly used on rape seeds, was examined for its potential in controlling fungal diseases in sunflowers. As an alternative disease control method, the
resistance inducing agent Benzo (1,2,3) thiadiazole-7-carbothioic (BTH) as the commercial available product BION (Syngenta) was tested under field conditions. Additionally, greenhouse experiments were conducted at Braunschweig in 2003 in order to observe the effect of BTH application on Sclerotinia infection at different growth stages under controlled conditions. Ammonium based liquid fertilizer injection, commonly called as CULTAN in Germany, was examined as an alternative plant nutrition method and for its potential to reduce fungal attacks. The bacterial mixture “Mikro-Vital” has been developed to supply the plants with nutrients and to suppress soil-borne fungal pathogens by soil application. Since fungal pathogens use sugar as the carbohydrate and energy source, sugar content of different plant parts was analyzed at different growth stages to find out possible correlation between the time fungal infection and the sugar content in these
plant parts. The three HO sunflower varieties showed good kernel and oil yield performance under both climatic conditions. However, the varieties showed low tolerance against fungal diseases and were severely infected in cold and wet years. Results indicate that the commercial fungicide does not reduce fungal infection rate and even showed in some cases yield suppression. Quality parameters were not affected by fungicide application. The resistance inducing product BION could suppress fungal disease severity only in
the first experimental year, but not in the following experimental years in 2003-2005. It slightly increased the oil content in the first year, whereas no significant change in oil content and composition was observed in a mean of all experimental years. Under greenhouse conditions, it could slow down the Sclerotinia infection but did not hinder it. Ammonium based liquid fertilization in general did not reduce fungal infection rate. Slight increases and decreases were observed in grain yield depending on the variety, location and year. It caused increase in oil content at Braunschweig and a decrease at Eckartsweier. Oil composition was not changed by the alternative fertilization method. Mikro-Vital application also could not proof as a method for control of fungal diseases. It resulted a slight increase in yield but only depended on the variety and this increase was not constant through the years. Only in warm and dry year, oil content was increased but in general neither oil content nor the composition was changed. Sugar analysis showed that there is still a high amount of sugar in the plant head at the end of the vegetation period which acts as attraction center for fungal  pathogens.