## 4 Discussion  
The lowest yield per vine and cluster weight was found in BS vines, and not those cluster-thinned at an intensity of 35%, as expected. It is probable that early source removal of six basal leaves immediately after berry set reduced assimilate supply and pressured the vine to select a certain number of berries that would ripen properly [5]. The lack of a significant decrease in yield, despite the low number of clusters left on the vine after  
Figure 2: PCA performed using the concentrations of 16 volatile compounds with OAV > 1 discriminated among wine samples produced from five canopy-management treatments. (**A**) Projections of 16 volatile characteristics based on latent PC factors 1 and 2, which together explained 73.68% of total variability. (**B**) Principal component analysis (PCA) of 15 wines (C1, C2, C3: control; VI, V2, V3: defoliation at veraison; CT1, CT2, CT3: cluster thinning; PF1, PF2, PF3: defoliation at preflowering; and BS1, BS2, BS3: defoliation at berry set) on the plane defined by the first two principal components. cluster thinning, was due to self-compensation increasing the grape cluster and berry weight [18; 19]. Those larger berries could decrease the skin-to-pulp ratio and aroma compound concentrations [18]. Regulation of yield with cluster-thinning or defoliation practices depends on vintage [5; 19; 20], agroecological conditions of location, and variety [19; 21; 22]. Despite studies describing the impact of defoliation or cluster thinning on aromatic compounds in berries, there are little data concerning their effect on the physiochemical and aroma composition of wine. Defoliation reduced berry TSS, final alcohol content, and pH, and increased the total acidity of Marastina wines, with the greatest effect with early defoliation treatments (BS and PF). Terpene and C\({}_{13}\) norisoprenoid compounds are important carriers of varietal aroma. In this study, defoliation at intensity of six basal leaves, regardless of the timing, reduced the total concentration of terpen in Marastina wines compared to the untreated C. Despite use of the same training system (Guyot) in this and in an experiment conducted on Malvazija Istarska [23], the reported beneficial impact of early defoliation on linalool, citronello, nerol, and geraniol was missing. Among the three defoliation treatments, the most individual and total sum of terpene compounds was in V wines, as reported previously for Sauvignon Blanc with 50% or 100% (six leaves) intensity of basal defoliation [6]. Defoliation early in the season had a strong impact on temperature and increase in evaporative and respiration rate of berries [24]. It could be that heat stress during herbaceous stage of berries led to a delay in the onset of accumulation of those compounds and an increase in the degradation and volatilization of already-synthesized compounds [25; 26]. Previous research placed the peak of terpene synthesis at two weeks after veraison, and the hypothesis that defoliation at veraison would increase certain terpenes was partly confirmed [27]. The CT wines had the highest total sum of terpenes, with the most abundant being linalool, terpinen-4-ol, _trans-_\(\beta\)-fernesene, and geraniol. Significantly, the increases in linalool and geraniol in CT wines while others remained constant may have been an indicator of a fully mature grape [28]. One of the most important norisoprenoids is \(\beta\)-damascenone, a carrier of sweet, fruity, floral, and honey aromatic notes. In white wines, the perception threshold of \(\beta\)-damascenone was 0.05 ug L\({}^{-1}\), as in hydroalcoholic solution (10-12%, \(v/v\), water/ethanol mixture) [29]. In our study, wines of all treatments had high concentrations of this compound. The esters that carry floral and fruity aromas in wine are yeast-derived compounds. CT wines had the highest concentrations of isoamyl acetate, isobutyl acetate, ethyl lactate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, ethyl furoate, diethyl succinate, and total sum of esters.