## 2 Materials and Methods  
### Plant Material and Experimental Conditions  
The study was conducted in a 2.79 ha experimental field located in southwest Sicily (37\({}^{\circ}\)31\({}^{\prime}\) N, 13\({}^{\circ}\)03\({}^{\prime}\) E, about 120 m a.s.l.) from 2015 to 2021. The climate conditions of the area are very common in many of the olive-growing districts of the Mediterranean countries, with an average annual rainfall of 680 mm for the seven years of trial (min 450 mm in 2020, max 940 mm in 2021). The orchard was planted in 2014 using 1-year-old self-rooted olive trees of the Sicilian cultivars Abunara, Calatina, and Nocellara del Belice. The first two are minor (neglected) cultivars of the autochthonous Sicilian germplasm. Nocellara del Belice is one of the widely grown cultivars (almost 20,000 ha) in the Southwest of Sicily, and its fruits are used both for table purpose (green ripe) or olive oil extraction. All three cultivars produce large fruits (5 g on average), easy to detach from the tree at veraison. Depending on the cultivar, tree height at planting varied from 60 (Calatina) to 100 cm (Nocellara del Belice). Two-hundred-sixteen trees of each of the three cultivars were planted in north-south-oriented rows at four planting densities: 2 \(\times\) 5 m (1000 trees/ha), 3 \(\times\) 5 m (666 trees/ha), 4 \(\times\) 5 m (500 trees/ha), and 5 \(\times\) 5 m (400 trees/ha). Trees at 2 \(\times\) 5 m were trained to central leader (CLx2), while those at 3 \(\times\) 5 m were trained to free palmette (FPx3). Both these tree shapes formed continuous walls about 3 m in height depending on the growth habit, the vigor of the cultivar, and the type of machinery to be used for harvesting: straddle for relatively thin canopies (no more 1.5 m wide) or shaker equipped with side-by-side interceptor frame for thicker canopies (no larger than 3 m). Trees at 4 \(\times\) 5 m were trained to small globe vase (GVx4) and kept at 3 m in height. Trees at 5 \(\times\) 5 m were trained to poly-conic vase (PVx5) and kept at 3.5 m in height.  
In all four planting systems, trees were lightly pruned starting at the end of the first growing season to obtain the desired training form. In trees trained to CL, the first primary branch was selected at about 60 cm from the ground and the following branches at 30 cm upward and rotating along the main stem to avoid reciprocal shading (Figure 1). In trees trained to FP, branches directed to the inter-row were removed, whereas growth of branches on the row was favored. Each tree included three main scaffolds, the first at 60 cm from the ground and the second and third at 160 and 260 cm, respectively (Figure 1). In each scaffold, fruiting branches were growing toward the inter-row. In GV, trees were initially trained as CL, but at the end of the second year, the main stem was topped at 180 cm, and five branches with a 45\({}^{\circ}\) angle from the vertical were selected (Figure 1). The PV form is one of the several variants of the classic vase and was developed half a century ago in Italy to favor olive canopy management from the ground, and it may be considered the reference training form in this study. This training form was obtained according to the information reported in the literature [31].  
Two self-compensating in-line drippers per plant, delivering 16 L/h, were used for weekly irrigation from July through mid-September. Trees were deficit irrigated using a water potential threshold of \(-\)2.0 MPa [32]. The total seasonal (4 th week of June to 1 st week of October) application rate ranged from 500 to 1300 m\({}^{3}\) ha\({}^{-1}\) year\({}^{-1}\), depending on planting density and season. All other conventional cultural cares were the same for all trees in trial. Trees were fertilized with 200 kg/ha\({}^{-1}\) of 20-5-10 NPK complex to the soil and with 60 kg of 20-0-20 in the irrigation water, for a total of 130, 25, and 80 g/tree of N, P, and K, respectively. Soil was cultivated at a 10-20 cm depth three times per year in mid-March, at the end of May, and at the end of August.