Acta Hortic. 1199. ISHS 2018. DOI 10.17660/ActaHortic.2018.1199.11 Proc. VIII Int. Olive Symposium Eds.: S. Perica et al. 69 Impact of weather conditions and drought stress on primary and secondary metabolites of olives from Slovenian Istra A. Miklavčič Višnjevec 1 , V. Valenčič 2 , T. Hladnik 2 , M. Podgornik 2,a , D. Bandelj 1 , M. Hladnik 1 , A. Baruca Arbeiter 1 , M. Bučar-Miklavčič 2,3 , E. Bešter 2 , S. Volk 2 , M. Pintar 4 and B. Butinar 2 1 University of Primorska, Faculty of Mathematics, Natural Sciences and Information Technologies, Glagoljaška 8, 6000 Koper, Slovenia; 2 University of Primorska, Science and Research Centre, Garibaldijeva 1, 6000 Koper, Slovenia; 3 LABS, LLC – Institute for Ecology, Olive Oil and Control, Zelena ulica 8c, 6310 Izola, Slovenia; 4 University of Ljubljana, Biotechnical Faculty, Agronomy Department, Jamnikarjeva 101, 1000 Ljubljana, Slovenia. Abstract Sugars, the primary metabolites of plants, play an important role in the process of olive ripening, as they provide energy for metabolic changes and serve as a source for the biosynthesis of fatty acids. Phenolic compounds, which are secondary metabolites, can be synthesized in plants as a reflection of stressful situations such as tissue damage and UV irradiation. The objective of this study was to assess the impact of different irrigation treatments (0, 15, 33, 40, and 100% crop evapotranspiration (ETc)) on primary metabolites (sugars, sugar alcohols) and secondary metabolites (phenolic compounds). In different phenological periods, the levels of oleuropein, sugars and sugar alcohols were determined in olives and leaf samples in the crop years 2014, 2015, and 2016. The levels of oleuropein in olive fruits and leaves were highest under the irrigation treatment of 40% ETc and decreased noticeably under the irrigation treatment of 100% ETc. The median levels of glucose were higher compared with the mannitol and fructose levels in olive fruits. Total determined sugars in olive fruits during maturation decreased. While significant correlations were found in olive fruits between determined sugars and sugar alcohols and different irrigation treatments, we did not observe any correlation between determined sugars and sugar alcohols in olive leaves and irrigation treatments. Our research confirmed the complexity of the content of oleuropein and sugars or sugar alcohols in the leaves and fruits of olive trees from Slovenian Istra, which depend on various factors, not just drought stress. Weaker and less obvious correlations between the studied compounds and drought stress might be a consequence of unusual rainfall in the studied crop years. Keywords: irrigation treatments, oleuropein, sugar alcohols, sugars INTRODUCTION A series of metabolic transformations appear during the process of maturation of olive fruits. Sugars are the major soluble compounds in the tissues of olives, and they play an important role, as they provide energy for metabolic changes. While oil is accumulated in the fruit, precursors for the synthesis of triacylglycerols originate from the leaves. Carbohydrate levels in the pericarp of olives reflect the inflow of metabolites from the leaves and serve as a source for fatty acid biosynthesis (Donaire et al., 1975; Simcox et al., 1979; Marsilio et al., 2001). Sugar alcohols in olive fruits may be important for metabolic transformation and the synthesis of storage material in fruits (Trip et al., 1964; Lewis and Smith, 1967; Marsilio et al., 2001). Wodner et al. (1988), Marsilio et al. (2001) and Seyyednejad et al. (2001) confirmed the complexity of the dynamics of sugars and sugar alcohols in the process of maturation of olives, depending on the cultivar and climate and other environmental factors. a E-mail: Maja.Podgornik@zrs-kp.si