Effect of a regulated deficit irrigation strategy in a hedgerow 'Arbequina' olive orchard on the mesocarp fatty acid composition and desaturase gene expression with respect to olive oil quality

The effect of three irrigation strategies on the olive oil quality in a hedgerow 'Arbequina' olive orchard with 1667 trees ha(-1) was assessed. Olive trees were fully irrigated, with the crop water demand replaced through daily irrigation (FI), or irrigated according to two regulated deficit irrigation (RDI) treatments, in which the total irrigation supplies amounted to 60% and 30% of the water supplied to the FI treatment. Oil content, fatty acid composition and desaturase genes expression in fruits from the three treatments were analysed. Although the total oil content and the amounts of the diverse lipid classes were not affected by the different irrigation treatments, changes in the fatty acid composition during the mesocarp development and ripening in the three irrigation treatments were detected. The 3ORDI strategy caused a decrease in the linoleic acid content in olive mesocarp and, therefore, in the olive oil. The lack of correlation with the expression of known oleate desaturase genes (OeFAD2-1, OeFAD2-2 and OeFAD6) points out to an un-identified oleate desaturase gene that could be repressed by water stress. Linolenic acid content and expression levels of plastidial linoleate desaturase genes (OeFAD7-1 and OeFAD7-2) increased under 3ORDI conditions at the beginning of fruit development. However, this effect was not noticeable in the olive oil because it was not observed during fruit ripening. All these data enlighten the molecular mechanisms related to the fatty acid desaturation in the oil of olive trees under water stress and point out to the 3ORDI as suitable strategy when olive quality is the main production target.