In the frame of this master thesis, we have searched and studied biotypes of 'Rebula' (Vitis vinifera L.) variety in seven older vineyards in Goriška brda winegrowing district in 2018 and 2019. We confirmed three biotypes of the 'Rebula' variety, namely a biotype with a cylindrical cluster (VG), a biotype with a conical cluster (SG) and a biotype with a millerandage cluster known as “crazy” 'Rebula' (NR). The evaluated OIV descriptors have shown several differences among biotypes, these are the colour of the upper part of the 4th leaf from the apex to the base of the shoot, shape of the teeth, shape of the petiole sinus, density of prostrate and erect hairs on main veins on lower side of blade, density of erect hairs on main veins on lower side of blade, in shape, length, width and density of the bunch, length and lignification of peduncle of primary bunch, number of wings of the primary bunch, and in length, width, uniformity of size and shape of berries. The phyllometry has reviled significant differences among biotypes in the length between the superior and basal teeth of the superior leaf carp (D1), internal angle between the third and fourth lateral veins to the first branching (), angle between the second and third lateral veins evaluated between the connections between the petiole sinus at L3 and L4 () and width of the teeth at the end of L4 (b2). Considering both vintages, biotype NR, in comparison to the other two biotypes, showed the significant lower weight of 100 berries (60.5-163.2 g), but the significantly highest soluble solids content (19.1-21.1 °Brix). In 2019, the significantly lowest soluble solids content (16,3 °Brix), while the highest titratable (6.09 g/l) and total (6.42 g/l) acidity were measured at SG biotype. The study confirmed that different biotypes of the 'Rebula' variety are still present in the Brda vineyards, which should be preserved through selection, otherwise the biotypes will be lost.
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