Water saving under drought stress is assured by stomatal closure driven by active (ABA-mediated) and/or passive (hydraulic-mediated) mechanisms. There is currently no comprehensive model nor any general consensus about the actual contribution and relative importance of each of the above factors in modulating stomatal closurein planta. In the present study, we assessed the contribution of passive (hydraulic) vs active (ABA mediated) mechanisms of stomatal closure inV. viniferaplants facing drought stress. Leaf gas exchange decreased progressively to zero during drought and embolism-induced loss of hydraulic conductance in petioles peaked to ~50% in correspondence with strong daily limitation of stomatal conductance. Foliar ABA significantly increased only after complete stomatal closure had already occurred. Rewatering plants after complete stomatal closure and after foliar ABA reached maximum values did not induced stomatal re-opening, despite embolism recovery and water potential rise. Our data suggest that in grapevine stomatal conductance is primarily regulated by passive hydraulic mechanisms. Foliar ABA apparently limits leaf gas exchange over long-term, also preventing recovery of stomatal aperture upon rewatering, suggesting the occurrence of a mechanism of long-term down-regulation of transpiration to favor embolism repair and preserve water under conditions of fluctuating water availability and repeated drought events.

One of the main objectives of wine grape growers in several viticultural areas throughout history has been the achievement of full ripening, i.e. maximum soluble solids concentration in the absence of apparent berry shrinkage. Recently, this target is somewhat losing its appeal since an increasing number of consumers from both domestic and foreign markets prefer lighter wines characterized by moderate alcohol content. The above scenario needs to be added of another actor, i.e. the global warming and its effects on vine growth and berry composition which can be summarized as it follows: (i) onset of flowering and veraison phenological stages occurs earlier; (ii) grape ripening is generally accelerated as per increment of sugar accumulation into the berries which, in turn, leads to higher alcohol content in the wine; (iii) faster depletion of organic acids in the juice and more rapid increase of pH values which, as a consequence, triggers high microbiological instability of the must during pre-fermentation; (iv) due to excessive heat summations and poor thermal excursion the overall aroma profile can result untypical shifting towards overripe; (v) uncoupling of technological (more accelerated) and phenolic (more delayed) ripening with negative effects on grape and wine aroma and flavor, especially in red grape varieties; (vi) higher frequency of berry withering up to sun burn damage. In the medium-to-long term these factors likely will affect the geographical distribution of viticulture and will require new breeding programs for selecting more adapted roostocks and scions, whereas in the short term, new management techniques able to mitigate these negative impacts are urgently needed. In this review, several tools including varietal and clonal choice, possible diversification of wines produced, suitable training system and rootstocks, traditional and innovative management techniques able to regulate a too much accelerated and/or unbalanced grape ripening process, will be presented and discussed. © 2014 Elsevier B.V

Previous studies indicate that the size-controlling capacity of peach rootstocks is associated with reductions of scion water potential during mid-day that are caused by the reduced hydraulic conductance of the rootstock. Thus, shoot growth appears to be reduced by decreases in stem water potential. The aim of this study was to investigate the mechanism of reduced hydraulic conductance in size-controlling peach rootstocks. Anatomical measurements (diameter and frequency) of xylem vessels were determined in shoots, trunks and roots of three contrasting peach rootstocks grown as trees, each with different size-controlling characteristics: ‘Nemaguard’ (vigorous), ‘P30-135’ (intermediate vigour) and ‘K146-43’ (substantially dwarfing). Based on anatomical measurements, the theoretical axial xylem conductance of each tissue type and rootstock genotype was calculated via the Poiseuille–Hagen law. Larger vessel dimensions were found in the vigorous rootstock (‘Nemaguard’) than in the most dwarfing one (‘K146-43’) whereas vessels of ‘P30-135’ had intermediate dimensions. The density of vessels per xylem area in ‘Nemaguard’ was also less than in ‘P30-135’and ‘K146-43’. These characteristics resulted in different estimated hydraulic conductance among rootstocks: ‘Nemaguard’ had higher theoretical values followed by ‘P30-135’ and ‘K146-43’. These data indicate that phenotypic differences in xylem anatomical characteristics of rootstock genotypes appear to influence hydraulic conductance capacity directly, and therefore may be the main determinant of dwarfing in these peach rootstocks.