Night temperature and intercepted solar radiation additively contribute to oleic acid percentage in sunflower oil

Oil fatty acid composition of sunflower (Helianthus annuus L.) closely depends on the environmental conditions during grain filling. Temperature and solar radiation are main environmental factors driving oil chemical composition, as revealed by experiments in which the effects of these variables were investigated separately. The present work aims at investigating whether both temperature and irradiance act independently or they interact in exerting their effects on oleic acid percentage of sunflower oil. With this purpose, minimum night temperature (MNT) and intercepted solar radiation (ISR) per plant were together modified during the grain filling period of the traditional sunflower hybrid ACA 885. Two experimental approaches were performed: (a) radiation was modified in three locations at different latitudes (location × radiation experiments), (b) radiation and temperature were modified in a factorial design within one location by using field shelters (in situ temperature × radiation experiments). Regardless location or year effect, oleic acid percentage increased with ISR per plant up to a maximum value, which depended on MNT. In situ temperature × radiation experiments showed that plant heating increased oleic acid percentage under any radiation condition assayed, while plant shading produced a drop in oleic acid that was independent of MNT. Statistically significant interaction between MNT and ISR per plant was not detected. A mathematical relationship that considered that MNT and ISR per plant additively contribute to oleic acid percentage was established and verified using data from location × radiation experiments. This equation predicted well independent experimental data from in situ temperature × radiation experiments.