## 4 Discussion  
### Traditional Monastrell Clones Show a High Variability in WUE  
Our results show that the choice of the clone had a significant impact on the vine water status, leaf photosynthesis, and vine water use, vigor, productivity, WUE, and berry and wine quality of cv. Monastrell, indicating the existence of a great phenotypic plasticity among traditional Monastrell clones in SE Spain and confirming the presence of significant levels of intracultivar genetic diversity (a high variability) in this variety [21; 22]. In the same way, a huge genetic variability between the clones with regards to their agronomic behavior and berry and wine composition has been found in other  
Figure 10: (**A**) Graphics representing changes in control of transpired water (_E_, leaf transpiration rate; TLA, total leaf area) for each clone under control and stress conditions (**A**), \(\text{WUE}_{\text{leaf}}\) (**B**) changes in yield, \(\text{WUE}_{\text{yield}}\), TLA (total leaf area) and \(\text{QI}_{\text{overall berry}}\) (**C**) and increments and decrements for each clone in yield, TLA, WUE and QI between control and stress treatments (irrigation treatments) (**D**) Data average from three years. (**B**). Diagram showing a classification of clones according to three criteria: tolerance to drought, productive water use efficiency, and quality of grapes and wines. Low-vigour clones (372, 276) and high-vigour clone 188 showed an equilibrium among moderate/high yield, drought tolerance, \(\text{WUE}_{\text{yield}}\), and high berry and wine quality. varieties (cvs. Tempranillo, Graciano, Sangiovese) [40; 41]. Similarly, other studies demonstrated that even the few genetic differences existing among clones of the same cultivar (i.e., cv. \"Nebbiolo\") can affect the physiological and agronomical aptitudes of the grapevine through fine transcriptional reprogramming events mainly linked to carbohydrate and secondary metabolic changes [17]. Our results indicate a specific clone-rootstock interaction when comparing abiotic stress tolerance (e.g., drought tolerance), water use efficiency, and oenological potential in different cultivars, as it has been previously described [9; 10]. It is important to note that large differences in \(A\), \(g_{s}\), and \(E\) (vine water use) were observed among Monastrell genotypes (Table 3), which demonstrates that some genotypes present large fluxes of CO\({}_{2}\) and water, and others, low gas exchange fluxes, as observed in clones from other varieties [12; 13]. Therefore, clones also play an essential role in the water stress response in grapevines. Although the rootstock plays a central role in the improvement of water use efficiency (WUE) [26], this study also shows a great variability in WUE among Monastrell clones at a leaf level (WUEleaf) (average \(A\)/\(g_{s}\) of 65-137 umol mol\({}^{-1}\), Table 3) and a plant level (average WUEyield between 10-30 kg m\({}^{-3}\), \(\xi^{13}\)Cberries, \(-\)24--27 %, Tables 3 and 5), indicating that intracultivar clones constitute a major source of variation in water use efficiency, as was also observed in different varieties [11; 12; 13; 14; 15]. The most productive water use-efficient clones (94 and 188, Table 5) showed very high WUEyield values (28-30 kg m\({}^{-3}\)), similar to the highest found in cv. Gaglioppo in Italy (9-29 kg m\({}^{-3}\)) [42]. The values of WUEyield reported in field-grown deficit irrigated grapevines vary widely depending on the rootstock and the edaphoclimatic and irrigation conditions [43]. In Monastrell vines grafted on different rootstocks in SE Spain, they ranged between 9-18 kg m\({}^{-3}\)[26].