## 1 Introduction  
Olive (_Olea europaea_ L.) is an important crop in most Mediterranean countries [1, 2, 3] and olive oil is one of the crucial elements, as well as the main source of fats, in the Mediterranean diet [4]. The origin of olive cultivation is deeply connected to the Mediterranean civilizations, which cultivated olive trees 6000 years ago [5]. Although olive cultivation has spread across the globe to all continents, countries in the Mediterranean basin remain the largest olive producers. Olive oil is the main product derived from olives and is distinguishable from other oils by aroma, taste, color, nutritive properties, as well as health beneficial effects which are some of the reasons for its increasing popularity worldwide [6]. These beneficial effects have been attributed to several features of olive oil: high monounsaturated fatty acids content (MUFA), and compounds such as carotenoids, tocoperheols and polyphenols [7]. Unsaturated acids comprise up to 85% of the oil composition while, at this fraction, oleic acid (C18:1) can range from 55-83%. Other fatty acids are represented in smaller amounts, such as linoleic acid (2.5-21.0%) and palmitic acid (7.5-20.0%), which comprise the majority of the saturated fats fraction, palmitoleic acid (0.3-3.5%), and others, such as \(\alpha\)-linolenic and gadoleic acid, represented in amounts smaller than 1% [8]. Less represented compounds in virgin olive oil, besides the glyceride fraction, comprise less than 2% by weight, with the polyphenic compounds in this group forming a significant portion, among which simple phenol hydroxytrosol and secoiridoid oleuropein can be highlighted due to their beneficial effects on human health [9; 10]. These fractions of olive oil, specific fatty acids and polyphenols are the main factors in the remarkable antioxidant potential of extra virgin olive oil. Studies have shown that a MUFA rich diet improved oxidative status measured through oxidation and endothelial injury markers and decreased the risk of inflammatory and degenerative diseases, such as Alzheimer's disease [11; 12; 13]. Consumption of olive oil, in general, has been associated with a decreased risk of obesity [14]. In addition to health beneficial MUFA properties, polyphenic compounds are known for their bioactive properties, such as antioxidant, anti-inflammatory, antimicrobial, anti-cancer and antihypertensive properties [15; 16]. The composition of both of these types of compounds is, however, not constant and is dependent on internal and external factors. Factors such as genotype, climate conditions, and fertilization can greatly influence the abundance and ratios of these compounds in olive oil. The effect of temperature on oleic acid content has been extensively researched [17; 18; 19]. Fatty acid profiles are largely dependent on the cultivar, which has also been extensively researched [20; 21]. In a similar manner, polyphenic contents and ratios of certain polyphenic compounds tend to change based on the olive cultivar, environmental factors, time of harvest, extraction, storage conditions and fertilization [22; 23; 24]. Of these mentioned factors, the effect of genotype tends to have a stronger effect on polyphenic content than others, such as in the research of [PERSON] [25] in which, out of five genotypes and three environmental effects (harvest date, season and location), clear grouping based on genotype was observed due to its prominent influence over environmental factors and the interactions of main effects. Foliar treatments of olive, such as applying nano-silicon spray, foliar particle films or amino, humic and fulvic acids, have shown potential for alleviating stress during olive growth, as well as impacting olive oil quality in terms of fatty acids and polyphenic contents [26; 27; 28]. The use of silicon (Si) has been previously addressed regarding its plant nutritional potential [29].