## 1 Introduction  
The positive impact on human health [1; 2] and its sensory properties are among the main aspects that make virgin olive oil (VOO) attractive to consumers. With respect to the sensory properties, the volatile fraction of VOO determines its aroma, which is mainly characterized by a mixture of green and fruity odor notes that make it a unique edible oil. The aroma of VOO is synthesized during the oil extraction process when enzymes and substrates come together as a result of the olive fruit crushing. Six straight-chain carbons (C6), aldehydes, C6 alcohols, and their corresponding esters are the most important compounds in VOO aroma [3; 4; 5]. The synthesis of these compounds depends mainly on the level of lipoxygenase (LOX) activity and the availability of substrates to be catabolizedthrough the LOX pathway during the process of obtaining the oil [6; 7]. This synthesis starts from polyunsaturated fatty acids, such as linoleic (LA) and linoleic (LnA) acids, by the consecutive action of LOX, hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) enzymatic activities to produce, respectively, the 13-hydroperoxide derivatives of the polyunsaturated fatty acids, the C6 aldehydes, and the C6 alcohols [3; 8; 9; 10]. Finally, the C6 alcohols can be substrates for ester production catalyzed by alcohol acyltransferase (AAT) enzymatic activities [3; 11]. Five straight-chain carbon compounds (C5) are also important to VOO aroma [5] and seem to be synthesized through another branch of the LOX pathway involving the production of a 1,3-pentene allylic radical that can dimerize to pentene dimers (PD), or to form C5 alcohols by reaction with a hydroxyl radical. These C5 alcohols may be converted into C5 carbonyl compounds via enzymatic oxidation by ADH. VOO is the only food product that requires a sensory analysis to be classified in commercial categories. This classification is ruled by the European Official Regulations for olive oil [12] and is carried out by certified test panels, in which the evaluation of taste (pungency and bitterness) and aroma play a very important role. In this regard, [PERSON] and [PERSON] [13] developed the statistical sensory wheel (SSW) for VOO to understand the connection between volatile compounds and odor characteristics in the oil. The SSW clusters into different sectors the sensory attributes of VOO together with the volatile compounds labeled with a particular sensory note, those in the green or ripe fruit sectors being the most important to VOO aroma. This sensory perception of a volatile compound depends on its odor activity value (OAV), the ratio between the concentration of the volatile compound and its odor threshold, so that only volatile compounds with an OAV higher than one contribute to VOO aroma. However, it should be mentioned that OAV values are only indicative of the contribution of the volatiles to the VOO overall aroma, since they do not take into account enhancement or suppression effects of different odorants and other non-volatile components present in the oils. The wide genetic patrimony is one of the key features of the olive tree. Much emphasis has been laid on the collection and conservation of olive genetic resources leading to the establishment of ex-situ germplasm banks. In this sense, the World Olive Germplasm Collection (WOGC), located in Cordoba, Spain, is an international reference due to the high number of accessions included and their high degree of identification and evaluation. Molecular markers and agronomical traits were used to study the patterns of genetic diversity and underlying genetic structure among olive accessions in the WOGC [14] and, as a result, a core set of 36 olive cultivars (Core-36), representing 10% of the whole germplasm bank, was established, which holds most of this genetic diversity (Table 1).