CONICET | Buscador de Institutos y Recursos Humanos

In intensive, high density olive orchards, the tree canopy is often managed without a sufficient understanding of how changes in the light environment as the tree grows or is pruned affect fruit growth and oil parameters. In the present study, we evaluated the role of shading on fruit development, oil accumulation, and oil composition by directly manipulating Photosynthetically Active Radiation (PAR). The level of PAR was reduced to 3%, 20%, 40% or 80% of inter-row full sunlight using shade cloth. These treatments were imposed on the north side (illuminated in the Southern hemisphere) of sixteen olive trees (n=4) for the variety `Arbequina´. Olive trees were shaded during periods of thirty days during October 2007 - January 2008 (i.e., spring summer). The fruit dry weight was reduced by 40% in the 3% PAR treatment compared to the control during the initial stage of fruit growth (first phase; October) and by 25% after pit hardening during the exponential growth stage (third phase, December). Shading (3% PAR) also caused a reduction in oil content (56% lower than the control) at the beginning of oil synthesis (third phase, December). During pit hardening, shading reduced the percentage of oleic acid in the fruits by 50%. However, the shading effect on fatty acid composition was less pronounced when treatments were applied during the more advanced stages of oil accumulation. Based on the four light levels used, fruit dry weight and oil content increased exponentially with increasing PAR until a threshold value of 40% was reached. In contrast, the percentage of oleic acid reached its threshold value at 20% PAR. In summary, the effects of shading on fruit growth, oil accumulation and oil composition depend strongly on the stage of fruit development and the threshold response value to PAR differs between parameters.

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