Crop-regulation techniques applied as preflowering defoliation (D), early cluster thinning at preflowering (ECT), and cluster thinning at lag-phase of berry growth (LCT) were tested over three seasons on high-yielding Vitis vinifera L. Sangiovese and compared to non-defoliated, unthinned control vines. Treatment severity consisted of removing primary leaves and any laterals developed from nodes 1 to 6 in D and of thinning 50% of clusters chosen from among distal clusters or those inserted on weak shoots in ECT and LCT plots. Although yield per vine was not as reduced in D (−32%) as in ECT and LCT treatments (−45%) as compared to the control, D vines also had largely improved sugar and total anthocyanin concentrations and the highest total phenolics. Yield components were also markedly affected by treatments: D vines had smaller clusters and berries, leading to improved cluster looseness and to higher relative skin and seed growth. While all crop-regulating treatments led to an increase in the final leaf-to-fruit ratio, parameters of technological maturity were essentially uncoupled, as equally high Brix levels corresponded to the highest titratable acidity in D and, conversely, to lowest titratable acidity and highest pH in ECT and LCT. Overall results showed that different final yield-grape composition patterns can be reached depending on the technique used for crop regulation as a primary consequence of a diversified degree of compensation triggered on single-yield components.

Background and Aims: Little work has been conducted on the effects that summer pruning operations have on the relative growth of grapevine berry parts. Our paper studies whether pre-bloom leaf removal is able to modify the proportions of seed, skin and flesh in ripe grapevines berries and the related effects on must composition.\ud \ud Methods and Results: Pre-bloom defoliation (D) of the first six basal leaves on main shoots was applied to the field-grown cvs Barbera and Lambrusco salamino (Vitis vinifera L.) in Italy's Po Valley and compared with non-defoliated controls. D showed reduced fruitset, hence yield per shoot, and concurrently improved must soluble solids and total anthocyanins in both cultivars as a likely result of increased leaf-to-fruit ratio (+3.4 cm2/g and +5.2 cm2/g for Barbera and Lambrusco, respectively) and improved relative skin mass (from 6.0 to 9.0% in Barbera and from 8.1 to 10.4% in Lambrusco). In both cultivars, skin and seed mass were highly correlated with total berry mass and changes in relative skin mass were generally not related to berry size.\ud \ud Conclusions: These results indicate that berry size per se is not the primary factor in determining final grape composition, which instead seems to depend upon factors differentially affecting the growth of the various berry components.\ud \ud Significance of the Study: Pre-bloom D induced a consistent, site and cultivar-independent increase in relative skin mass suggesting this effect being strongly physiologically regulated

Grape berry composition mainly consists of primary and secondary metabolites. Both are sensitive to environment and viticultural management. As a consequence, climate change can affect berry composition and modify wine quality and typicity. Leaf removal techniques can impact berry composition by modulating the source-to-sink balance and, in turn, may mitigate some undesired effects due to climate change. The present study investigated the balance between technological maturity parameters such as sugars and organic acids, and phenolic maturity parameters such as anthocyanins in response to source-sink modulation. Sugar, organic acid, and anthocyanin profiles were compared under two contrasting carbon supply levels in berries of cv. Cabernet Sauvignon and Sangiovese collected at 9 and 14 developmental stages respectively. In addition, whole-canopy net carbon exchange rate was monitored for Sangiovese vines and a mathematic model was used to calculate the balance between carbon fixation and berry sugar accumulation. Carbon limitation affected neither berry size nor the concentration of organic acids at harvest. However, it significantly reduced the accumulation of sugars and total anthocyanins in both cultivars. Most interestingly, carbon limitation decreased total anthocyanin concentration by 84.3 % as compared to the non source-limited control, whereas it decreased sugar concentration only by 27.1 %. This suggests that carbon limitation led to a strong imbalance between sugars and anthocyanins. Moreover, carbon limitation affected anthocyanin profiles in a cultivar dependent manner. Mathematical analysis of carbon-balance indicated that berries used a higher proportion of fixed carbon for sugar accumulation under carbon limitation (76.9%) than under carbon sufficiency (48%). Thus, under carbon limitation, the grape berry can manage the metabolic fate of carbon in such a way that sugar accumulation is maintained at the expense of secondary metabolites.

Analysis of the spectral response of vegetation using optical sensors for non-destructive remote monitoring represents a key element for crop monitoring. Considering the wide presence on the market of unmanned aerial vehicle (UAVs) based commercial solutions, the need emerges for clear information on the performance of these products to guide the end-user in their choice and utilization for precision agriculture applications. This work aims to compare two UAV based commercial products, represented by DJI P4M and SENOP HSC-2 for the acquisition of multispectral and hyperspectral images, respectively, in vineyards. The accuracy of both cameras was evaluated on 6 different targets commonly found in vineyards, represented by bare soil, bare-stony soil, stony soil, soil with dry grass, partially grass covered soil and canopy. Given the importance of the radiometric calibration, four methods for multispectral images correction were evaluated, taking in account the irradiance sensor equipped on the camera (M1–M2) and the use of an empirical line model (ELM) based on reference reflectance panels (M3–M4). In addition, different DJI P4M exposure setups were evaluated. The performance of the cameras was evaluated by means of the calculation of three widely used vegetation indices (VIs), as percentage error (PE) with respect to ground truth spectroradiometer measurements. The results highlighted the importance of reference panels for the radiometric calibration of multispectral images (M1–M2 average PE = 21.8–100.0%; M3–M4 average PE = 11.9–29.5%). Generally, the hyperspectral camera provided the best accuracy with a PE ranging between 1.0% and 13.6%. Both cameras showed higher performance on the pure canopy pixel target, compared to mixed targets. However, this issue can be easily solved by applying widespread segmentation techniques for the row extraction. This work provides insights to assist end-users in the UAV spectral monitoring to obtain reliable information for the analysis of spatio-temporal variability within vineyards.

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.