Antioxidant status, biochemical and hormonal responses involved in the response of Olea europaea L. to water deficit induced by PRD irrigation

Changes in antioxidant 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. 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 for proline, total soluble sugars, phenols and flavonoids, and the lowest ones for MDA and H2O2. The increase in SOD, CAT and POD activity and the reduction and 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 ABA and the highest levels of JA, SA and IAA. PRD irrigation also induces a higher accumulation of ABA, JA and IAA in dried roots than in wetted ones. Taken together, 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