In 2007, newspapers reported a decrease in oilseed rape Omega-3 fatty acid content, which was related to the breeding of modern varieties. The goal of the present paper was to evaluate this hypothesis and to document the role of temperature in the observed phenomenon. At Changins research Station, a significant decrease in alpha-linolenic acid content by a fourth of its initial value was registered over 8 years in a panel of varieties, while a 2.6 points oil content increase was observed in new-bred varieties. Moreover, a negative relationship between oil- and linolenic-acid content was established. Nonetheless, the breeding of modern varieties with improved oil content cannot be pointed out as major cause to explain the observed erosion in Omega-3 fatty acid contents. Similar decreases in alpha-linolenic acid content were also observed in two cultivars continuously grown over this period of time. Omega-3 fatty acid synthesis is negatively influenced by high night temperature during seed growth, a 20 days period usually taking place in June in the lowland conditions of Switzerland. Meteorological records for these regions show a 2.6 °C minimal temperature increase in June over the last 20 years. This trend could explain most of the observed erosion of Omega-3 fatty acid content in rapeseed oil.
Temperature and nutritional quality of rapsed oil