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

Based on earlier findings showing the effectiveness of preflowering leaf removal at reducing yield in several Vitis vinifera L. genotypes, a 3-year study was carried out on Sangiovese vines to evaluate how the technique also affects vegetative growth, wood carbohydrates reserves, and specific physiological traits such as intrinsic water use efficiency (WUEi) and leaf chlorophyll fluorescence. Early defoliation (D) applied before flowering with elimination of ~80% of the leaf area as compared with a non-defoliated control (C) was confirmed as quite effective in limiting yield per vine, cluster weight, cluster compactness and rot incidence, and berry set and mass in two of three seasons. Defoliation also markedly improved relative berry skin mass regardless of season. Vine vigor (pruning weight, cane diameter, and main leaf area) was significantly reduced in D vines (2008–2009 data), whereas vine capacity as total leaf area per vine was not. The leaf-to-fruit ratio dropped dramatically after defoliation to 1 m²/kg in D vines, which recovered thereafter and had a higher ratio from veraison onward. Intrinsic WUE and tolerance to photoinhibition increased in D vines for both main and lateral leaves, which were formed after leaf stripping and which had reached full maturity by the time measurements were made. Berry sugaring was accelerated in D vines, which also showed, at harvest, higher must Brix and phenolic and anthocyanin concentrations than C vines as well as more stable anthocyanins in the wine.

Several remote sensing technologies have been tested in precision viticulture to characterize vineyard spatial variability, from traditional aircraft and satellite platforms to recent unmanned aerial vehicles (UAVs). Imagery processing is still a challenge due to the traditional row-based architecture, where the inter-row soil provides a high to full presence of mixed pixels. In this case, UAV images combined with filtering techniques represent the solution to analyze pure canopy pixels and were used to benchmark the effectiveness of Sentinel-2 (S2) performance in overhead training systems. At harvest time, UAV filtered and unfiltered images and ground sampling data were used to validate the correlation between the S2 normalized difference vegetation indices (NDVIs) with vegetative and productive parameters in two vineyards (V1 and V2). Regarding the UAV vs. S2 NDVI comparison, in both vineyards, satellite data showed a high correlation both with UAV unfiltered and filtered images (V1 R² = 0.80 and V2 R² = 0.60 mean values). Ground data and remote sensing platform NDVIs correlation were strong for yield and biomass in both vineyards (R² from 0.60 to 0.95). These results demonstrate the effectiveness of spatial resolution provided by S2 on overhead trellis system viticulture, promoting precision viticulture also within areas that are currently managed without the support of innovative technologies.