The phenolic compounds, oleuropein and hydroxytyrosol are considered the main active compounds of the olive leaf, which have been proven to have anti-cancer, anti-inflammatory and antimicrobial effects. Oleuropein and hydroxytyrosol, as well as other phenols, have a specific role in protecting plants and increasing resistance to phytopathogenic fungi, which can be of crucial importance for sustainable olive cultivation in general. Phenols and polyphenols are ubiquitous compounds in plants that play an important role in the host plants defence mechanism against filamentous fungi. The importance of phenol, in addition to increasing the plants resistance to pathogens, is also evident in the production of functional food and nutraceuticals, as well as natural-based medicines for treating oral diseases. The need to find new therapeutic procedures in the treatment of pathological conditions of the oral cavity has led to increased interest in the use of natural substrates. It has been proven that agricultural practices can increase the phenol content in olive leaves. So far, only a few studies have focused on studying the influence of mineral nutrition on the composition of phenols in olive leaves. In this project, a whole series of experiments are planned to determine the influence of certain mineral nutrients (N, Ca, Mg, Mn, Zn, Cu and B) and elicitors (phosphite and potassium silicate) on the composition of phenols in the olive leaf of different varieties. The impact of the previously selected mineral nutrient or elicitor, which proves to be the most effective in increasing the level of phenol, on the development of peacock eye disease caused by the phytopathogenic fungus Venturia oleaginea (syn. Spilocaea oleaginea) will also be evaluated. The development of the disease will be monitored on treated olives in the field or under controlled conditions in the greenhouse. The effect of the best treatment will be tested through the quality of olive oil on the Leccino variety grown on different terroirs. As part of this project, it is also planned to carry out preclinical and clinical research on the effect of olive leaf extract on oral candidiasis.