Water status, biochemical and hormonal changes involved in the response of Olea europaea L. to water deficit induced by partial root-zone drying irrigation (PRD)

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Changes in the plant water status, biochemical and hormonal responses, were investigated in three olive cultivars (Arbequina, Arbosana and Chetoui) grown in a super-high-density orchard under partial root-zone drying (PRD) irrigation. Four irrigation treatments were applied during two growing seasons (2015 and 2016); control treatment (100 % ETc) irrigated at 100 % of crop evapotranspiration on both parts of the root-zone and three PRD irrigation treatments (100 % PRD, 75 % PRD and 50 % PRD) irrigated at 100 %, 75 %, and 50 % of crop evapotranspiration only on one alternated part of the root-zone. The results indicated that the three studied olive cultivars showed a clear difference in their response to PRD irrigation. Arbequina cultivar has shown a conservative strategy for using water since relative water content (RWC) and stem water potential (Ψstem) were reduced more in Arbosana and Chetoui under PRD irrigation. In fact, PRD irrigation has led to a strong activation of secondary metabolites with antioxidant properties such as pigments, phenols and flavonoids. Other metabolic changes, including the accumulation of soluble sugars and proline have been also triggered by PRD irrigation. Among the studied cultivars, Arbequina displayed the highest levels of proline, total soluble sugars, phenols and flavonoids, and the lowest ones for Malondialdehyde (MDA) and hydrogen peroxide (H2O2).The increase in Superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POD) activity and the reduction in polyphenoloxidase (PPO) activity under PRD irrigation were more pronounced in 2016 season with highest activities obtained from cultivar Arbequina.For all the three cultivars, PRD irrigation increased phytohormones concentration in both, roots and leaves and the highest levels were recorded in 2016. In leaves, Arbequina showed the lowest levels of abscisic acid (ABA), and the highest levels of jasmonic acid (JA), salicylic acid (SA) and indole-3-acetic acid (IAA). PRD irrigation also induces a higher accumulation of ABA, JA and IAA in dried roots than in wetted ones.Taken together, physiological and biochemical mechanisms induced by PRD irrigation were more effective in Arbequina suggesting better protection of their foliar functions compared to other cultivars and its higher adaptability to PRD.