No abstract

M4 is a relatively new rootstock that was selected for increased resilience of vineyards across hot regions where meteorological drought is often coupled to water scarcity. However, M4 has thus far been tested only against water-stress sensitive rootstocks. Against this backdrop, the aim of the present work is to examine the water status and gas exchange performances of vines grafted to M4 in comparison to those of vines grafted to a commercial stock that is drought-tolerant, 1103 Paulsen (1103P), under a progressive water deficit followed by re-watering. This study was undertaken on Grechetto Gentile, a cultivar that is renowned for its rather conservative water use (near-isohydric behavior). While fifty percent of both grafts were fully irrigated (WW), the remaining underwent progressive water stress by means of suspending irrigation (WS). Soil and leaf water status, as well as leaf gas exchanges, along with chlorophyll fluorescence, were followed daily from 1 day pre-stress (DOY 176) until re-watering (DOY 184). Final leaf area per vine, divided in main and lateral contribution, was also assessed. While 1103P grafted vines manifested higher water use under WW conditions, progressive stress evidenced a faster water depletion by 1103P, which also maintained slightly more negative midday leaf water potential (Ψleaf) as compared to M4 grafted plants. Daily gas exchange readings, as well as diurnal assessment performed at the peak of stress (DOY 183), also showed increased leaf assimilation rates (A) and water use efficiency (WUE) in vines grafted on M4, which were also less susceptible to photosynthetic downregulation. Dynamic of stomatal closure targeted at 90% reduction of leaf stomatal conductance showed a similar behavior among rootstocks since the above threshold was reached by both at Ψleaf of about −1.11 MPa. The same fractional reduction in leaf A was reached by vines grafted on M4 at a Ψleaf of −1.28 MPa vs. −1.10 MPa measured in 1103P, meaning that using M4 as a rootstock will postpone full stomatal closure. While mechanisms involved in improved CO2 uptake in M4-grafted vines under moderate-to-severe stress are still unclear, our data support the hypothesis that M4 might outscore the performance of a commercial drought-tolerant genotype (1103P) and can be profitably used as a tool to improve the resilience of vines to summer drought.

In many viticulture regions, multiple summer stresses are occurring with increased frequency and severity because of warming trends. Kaolin-based particle film technology is a technique that can mitigate the negative effects of intense and/or prolonged drought on grapevine physiology. Although a primary mechanism of action of kaolin is the increase of radiation reflection, some indirect effects are the protection of canopy functionality and faster stress recovery by abscisic acid (ABA) regulation. The physiological mechanism underlying the kaolin regulation of canopy functionality under water deficit is still poorly understood. In a dry-down experiment carried out on grapevines, at the peak of stress and when control vines zeroed whole-canopy net CO2 exchange rates/leaf area (NCER/LA), kaolin-treated vines maintained positive NCER/LA (~2 µmol m−2 s−1) and canopy transpiration (E) (0.57 µmol m−2 s−1). Kaolin-coated leaves had a higher violaxanthin (Vx) + antheraxanthin (Ax) + zeaxanthin (Zx) pool and a significantly lower neoxanthin (Nx) content (VAZ) when water deficit became severe. At the peak of water shortage, leaf ABA suddenly increased by 4-fold in control vines, whereas in kaolin-coated leaves the variation of ABA content was limited. Overall, kaolin prevented the biosynthesis of ABA by avoiding the deviation of the VAZ epoxidation/de-epoxidation cycle into the ABA precursor (i.e., Nx) biosynthetic direction. The preservation of the active VAZ cycle and transpiration led to an improved dissipation of exceeding electrons, explaining the higher resilience of canopy functionality expressed by canopies sprayed by kaolin. These results point out the interaction of kaolin with the regulation of the VAZ cycle and the active mechanism of stomatal conductance regulation.

No abstract

Background and Aims: The postponement of spur pruning after budburst has recently been proposed as a simple and inexpensive way to delay sugaring, maintain acidity and contain yield in spur-pruned trellised grapes. Yet, no long-term data are available for the widely adopted cane pruning system. Methods and Results: Mature field grown Vitis vinifera L. cv. Pinot Noir vines were subjected for three consecutive years to the following treatments: standard winter pruning (WP), double pruning (DP), where shortening and positioning of the selected cane is postponed, and late pruning (LP), where all pruning operations are postponed. Postponed pruning was performed when shoot growth from node 10 of the unpruned canes had reached an average stage of more than three unfolded leaves. Phenological and ripening dynamics, yield components and must composition were determined. Double pruning did not affect phenology and overall vine performance compared to that of WP. Conversely, LP significantly delayed ripening over 2 trial years; LP also slightly increased whole-vine and single-cane phenological variability, whereas yield per vine was reduced by 35% as compared to that of WP because of lower shoot fruitfulness. Conclusions: If repeated over several seasons, late WP applied to a cane-pruned system when the distal part of the cane has already burst an average of three leaves can become effective at delaying phenology and extending maturity into a cooler season. Significance of the Study: We have validated a simple technique suitable for preserving balanced must composition required for a range of sparkling wine styles.