# Effect of Selected _Trichoderma_ Strains and Metabolites on Olive Drupes
## 1 Introduction  
Since ancient times olive trees (_Olea europae_ L.) have been cultivated throughout the Mediterranean area for their fruits and oil production. Each country has its local cultivars because the human selection and pedoclimatic conditions have resulted in genetic variations [1; 2; 3; 4]. In Italy, many trees sprout spontaneously, and oil and table cultivars are grown mainly in Calabria, Apulia, Sicily, and Campania, where centuries-old trees and archaeological finds document their presence from old times [5]. Extravingin olive oil (EVOO) is obtained from crushing the olive drupe and separating olive oil by pressure, centrifugation, and percolation (selective filtration process) [6]. EVOO is present in all variants of the Mediterranean diet. The latter is a healthy diet adopted by the Italian and Greek population in the 1960s [7], reducing the risk of cardiovascular disease, cancer, type 2 diabetes, andcognitive disorders [8]. It is characterized by high consumption of vegetables, fruit, salads, bread, whole grains, legumes/beans, nuts, seeds, moderate use of wine, and EVOO as the primary source of fat [8]. The EVOO has protective effects on human health due to the high content of monounsaturated fatty acids (MUFAs) and secondary bioactive molecules, including phenolic compounds, tocopherols, phytosterols, and carotenoids [9]. The phenolic compounds in EVOO range from 50 to 800 mg/kg [10; 11]. They consist of phenolic alcohols (e.g., tyrosol and hydroxytyrosol), phenolic acids (e.g., vanillin, caffe, coumarin, protocathic, ferulic, and p-hydroxybenzoic), flavones (e.g., apigenin, apigenin-7-O-glucoside, luteolin, luteolin-7-O-glucoside), lignans (e.g., pinoresinol and acetoxypinoresinol), and secorioids (e.g., oleacein, oleuppein, oleocanthal, and p-HPEA-EA) [12] responsible for EVOO bitterness, pungency, fragrance, and antioxidative properties [13]. Fruit's maturation, cultivar varieties, pedoclimate condition [14], and the type of oil extraction processes affect the phenolic quality and concentration [15]. The oleuppein, tyrosol, and hydroxytyrosol (the main phenolic compounds in EVOO) [12] have antioxidant, anti-inflammatory, immunomododulatory, and neuroprotective activities [16]. The EVOO's polyphenols protect blood lipids against oxidative stress [17; 18]. Therefore, the EVOO's phenolics are used in supplements for the prevention of chronic degenerative diseases such as cardiovascular diseases and cancer [19], in antiaging cosme [20; 21], in the food industry as flavorings or preservers [22; 23; 24], and in functional foods preparations [25; 26]. Olive plants make the phenolics in response to abiotic stress and pathogen attack [27; 28; 29; 30; 31; 32]. [PERSON] et al. in 2020 and 2021 investigated the effects of some _Trichoderma_ strain applied to olive trees to evaluate a selective phenols production [33; 34]. Nowadays, fungi belonging to the genus _Trichoderma_ are commonly used in agriculture as biocontrol agents (they inhibit soils and air diseases) and plant growth promoters [35; 36]. They also enhance the abiotic stress tolerance (e.g., salinity, drought), yields production, nutritional uptake, leaf area, root system growth, and activate protective mechanisms against oxidative injury [37; 38]. Some _Trichoderma_ strains produce secondary metabolites such as 6-pentyl-a-pyrone (volatile antibiotics), heptelidic acid, and peptaibols to help in metal transport, symbiosis, differentiation, and competition with another organism [39; 40], and phenols against oxidative damage [41; 42; 43]. Phenols decrease cardiovascular pathologies, hypoglycemia, hypotension, and hypocholesterolem and prevent angiogenesis, inflammation [44], and cancer [45]. In the present work, we report the effect of selected _Trichoderma_ strains (e.g., _T. asperellum_ KV906, _T. harzianum_ strains TH1, M10, and T22; and _T.