Olive tree physiology and chemical composition of fruits are modulated by different deficit irrigation strategies

To overcome constrains affecting olive groves, cropping practices focusing on agronomic water use efficiency and their impact on quality parameters must be investigated. We evaluated the response of olive trees (Olea europaea, cv. Cobrançosa) to different water regimes, full irrigation (FI, 100% ETc) and three deficit irrigation strategies (DIS) (regulated (RDI, irrigated with 80% of crop evapotranspiration (ETc) in phases I and III of fruit growth and 10% of ETc in the pit hardening stage) and two continuous sustained strategies (SDI), a conventional SDI (27.5% of ETc), and a lowfrequency irrigation adopted by the farmer (SDIAF, 21.2% of ETc). RESULTS The effects of water regimes on the plant water status, photosynthetic performance, metabolites fluctuations and fruit quality parameters were evaluated. All DIS treatments enhanced leaf tissue density, RDI and SDI generally did not affect leaf water status and maintained photosynthetic machinery working properly, while SDIAF treatment impaired olive tree physiological indicators. DIS treatments maintained the levels of primary metabolites in leaves, but SDIAF plants showed signs of oxidative stress. Moreover, DIS treatments led to changes in the secondary metabolism, both in leaves and in fruits, with increased total phenolic compounds, ortho-diphenols, and flavonoids concentrations, and higher total antioxidant capacity, as well higher oil content. Phenolic profiles showed the relevance of an early harvest in order to obtain higher oleuropein levels with associated higher health benefits. CONCLUSION Adequate DIS are essential for sustainable olive growing, as they enhance the competitiveness of the sector in terms of olive production and associated quality parameters.