## 1 Introduction  
Pistachio (_Pistacia vera_ L.) is a nut tree species native to Western Asia and Asia Minor that can be cultivated under drought and saline conditions [1]. Iran, USA, Turkey, China and Syria are the world's main pistachio producers [2]. In Italy, pistachios have been historically produced in Sicily, on lava rich soils in a niche area around Mount Etna [3]. More recently, cultivation also expanded to the center of the Island [4]. Even though the Italian production represents less than 1% of the worldwide production (3864 tons) [2], it is characterized by very high quality and sold at higher prices than pistachio nuts from other countries [2; 5; 6; 7]. In particular, it is globally appreciated for the its intense green color and high nutrients content as well as its organoleptic properties [5; 8]. Other factors that make Italian pistachios unique are the different processing methods and final use. In California, the second worldwide producer after Iran [2], pistachios are primarily sold as snack food, roasted with or without salt [9], while Sicilian pistachios, locally known as \"green gold\", are mostly sold as fresh product, usually dried, and used in the confectionary industries as ingredients for cakes, pastries, ham, mortadella and ice creams [8]. During the roasting process, several thermal and chemical reactions occur that change some aromatic characteristics of the nuts. Specifically, it has been reported that roasted pistachios have higher concentrations of volatiles compounds than the raw ones [10]; moreover, chlorophylls are susceptible to heat and during the roasting process are converted to pheophytins and pyropheeophytins, causing the color to alter [11]. Recently, the popularity of pistachio nuts increased due to its health benefits [2, 5, 8, 12, 13]. From the nutritive point of view, pistachio fat content is about 50-60% of total nut weight depending on the cultivars [14]. The fatty acid composition is dominated mostly by oleic acid, followed by linoleic and palmitic acids [14, 15, 16, 17]. Furthermore, the organoleptic quality plays an important role for pistachio industry from the commercial point of view. The organoleptic quality of the pistachio nut is essentially correlated to the volatile profile which determines its flavor [18], and to the chlorophyll content which affects the internal kernel color [8]. Regarding the volatile composition, the terpen class has already been identified as main group in the cultivar Kerman and in several other Iranian and Turkish varieties, with \(\alpha\)-Pinene, D-Limonene and \(\beta\)-Myrcene as main constituents of the terpenes class [10, 17, 18, 19, 20, 21]. [PERSON] and [PERSON] [22] were the first to study the metabolism of the chloroplast pigments in pistachio nuts and reported the presence of chlorophylls a and b, \(\beta\)-carotene and lutein. [PERSON] [15] analyzed the variability of chlorophylls levels in different pistachio cultivars from several countries and found the highest chlorophylls content in pistachio nuts from Italy. [PERSON] and [PERSON] [23] also reported similar results. These studies showed a clear effect of the genotype on pistachio nuts' quality and sensory profile, but they do not deepen the effect of management practices on nuts' quality. In the Mediterranean Basin, pistachios have been traditionally cultivated under rainfed conditions [1, 3, 24], but in recent years the number of irrigated pistachio orchards have increased because of the well-claimed positive influence of irrigation on orchard productivity [25, 26, 27]. Despite the large literature showing correlation between water status and productivity, no clear information is available on the influence of trees' water status on pistachio nuts' quality. The only two studies that are available show no effect of irrigation on chlorophylls content but a negative impact on volatile composition [17, 21]. However, the irrigation treatments applied in these studies were aiming to match full crop evapotranspiration.