## 4 Discussion
### Clone Classification According to Drought Tolerance, Vine Performance, and  
_Oenological Potential_  
Drought tolerance is defined as the ability of plants to sustain a certain level of physiological activity through the regulation and fine tuning of thousands of genes and various metabolic pathways to minimize the resulting damage; it involves cell-to-cell to whole-plant level hydraulic or metabolic readjustment and hormone signalling able to control growth under water deficit [89]. However, when we look at crop plants, the features that confer drought tolerance are far from clear. Compared to the situation of plants growing in the wild, which can only rely on their repertoire of weapons and solutions to cope with stresses, crops in agriculture can be protected through human intervention (irrigation, fertilizer application, disease control, etc.). As a result, plants can take a competitive growth strategy, rather than a stress tolerant or ruderal strategy [90]. The main reason for this contrast is that the traits we associate with drought-tolerant species (xerophytes) typically concern survival during drought, whereas with crops we are concerned with production; insofar as the term \"drought tolerance\" has any useful meaning in an agricultural context, it must be defined in terms of yield in relation to a limiting water supply [91]. Thus, from the point of view of agriculture, drought tolerance must comprise not only the ability to cope with a stress factor, but also the capacity to maintain productivity (the achievement of a stable yield and good quality) within the current season and in the long-term, and equally the ability to avoid negative carry-over effects, and perhaps drought-induced mortality, across many seasons [54; 55]. In addition, a more drought-tolerant plant would be able to maintain its stability and homeostasis better and longer under soil water deficit, and this will probably be acquired through different mechanisms [46]. As in winegrapes the main concern is not to reach a high productivity and water saving, but rather to achieve the highest quality of grapes for premium red wine production, maintaining an optimum yield and ensuring economic returns to the grower [50], in this study, we have classified Monastrell clones in accordance to three relevant aspects: (1) drought tolerance, (2) productive water use efficiency, and (3) berry and wine-quality potential, looking for an optimum balance among these three traits (Figure 10B). In conclusion, taking into account the physiological and agronomical behavior of the clones under irrigated and water stress conditions, this study has revealed the following: (a) The most drought tolerant clone (i.e., clone 4) was not necessarily the most productive (8600 kg ha\({}^{-1}\)), the most water use efficient (average of 25 kg m\({}^{-3}\)), nor the one that presented a better grape and wine quality (Table 8, Figure 10). This clone had a different physiological behavior than the rest of the clones and did not show water conservation mechanisms under water stress conditions, being classified as a water spender (with an optimistic behavior); (b) The most productive and efficient clone (i.e., clone 94)(11,566 kg ha\({}^{-1}\), average WUE\({}_{\text{yield}}\) of 30 kg m\({}^{-3}\)) was also a drought-tolerant clone, but presented the highest yield and berry weight and the worst berry and wine quality, with the lowest polyphenolic concentration and aromatic/nutraceutical potential. Moreover, under lower irrigation volume (2021), both clones (94 and 4) enhanced WUE\({}_{\text{yield}}\) by 41% and 97%, respectively (compared to the average WUE\({}_{\text{yield}}\) for 2018-2020), but did not improve QIs.