Biosynthesis of the sesquiterpene rotundone in Vespolina grapes during berry ripening was investigated over two consecutive seasons, revealing that the compound accumulates from veraison to harvest and reaches relatively high concentrations (up to 5.44 μg/kg). Rotundone levels up to 1.91 μg/kg were also found in clones of Gruener Veltliner, a white grape variety known to give 'peppery' wines. These concentrations are higher than those reported for Syrah grapes and are similar to the levels found in some plants. Rotundone was shown to accumulate almost exclusively in berry exocarp, suggesting that skin contact during winemaking could be used to modulate the peppery character of red wine. However, rotundone yield after the winemaking process was relatively low. Indeed, only 10% of the rotundone present in grapes was extracted during fermentation, and only 6% was recovered in bottled wine. The results presented in this work provide key knowledge for manipulation of the peppery character of wine in order to optimize the intensity of this characteristic wine aroma.

Two chemical classes of flavonoids, the flavan-3-ols (catechins and proanthocyanidins) and the anthocyanins, are the natural antioxidants present at the highest concentration in red grape and wine. In the berry, the anthocyanins are localized in the skins, similarly to other highly bioactive phenolics of grape such as the resveratrols and the flavonols, while the flavan-3-ols are contained both in the skins and seeds. During winemaking, only a fraction of the grape flavonoids are selectively extracted into the wine, with a time course and a final yield strongly depending on the grape variety. The knowledge of the diverse and cultivar-specific characteristics of the grape is therefore critical to the appropriate design of the winemaking process. By means of a selective extraction method specifically designed to mimic the winemaking process, it was possible to analyze the "phenolic potential of red grape," thus obtaining quantitative information about amount and localization of the extractable flavonoids in the grape. Twenty-five high-quality red grape cultivars (V. vinifera) were studied, including 4 of the worldwide leading cultivars and 21 Italian cultivars with the highest reputation for the production of both young and aged premium red wines. The results clearly indicate that the grape variety plays a central role in determining both the absolute amount of the flavonoids, and the distribution between the berry skin and seeds of the flavan-3-ols. The very high biodiversity of the red grape cultivars in terms of flavonoids indicate a largely under-exploited opportunity to produce a range of diverse premium wines with optimized levels of natural antioxidants.

Summary To alleviate biotic and abiotic stresses and enhance fruit yield, many crops are cultivated in the form of grafted plants, in which the shoot (scion) and root (rootstock) systems of different species are joined together. Because (i) the plant species determines the microbial recruitment from the soil to the root and (ii) both scion and rootstock impact the physiology, morphology and biochemistry of the grafted plant, it can be expected that their different combinations should affect the recruitment and assembly of plant microbiome. To test our hypothesis, we investigated at a field scale the bacterial and fungal communities associated with the root system of seven grapevine rootstock–scion combinations cultivated across 10 different vineyards. Following the soil type, which resulted in the main determinant of the grapevine root microbial community diversity, the rootstock–scion combination resulted more important than the two components taken alone. Notably, the microbiome differences among the rootstock–scion combinations were mainly dictated by the changes in the relative abundance of microbiome members rather than by their presence/absence. These results reveal that the microbiome of grafted grapevine root systems is largely influenced by the combination of rootstock and scion, which affects the microbial diversity uptaken from soil.

Background and Aims Laboratory and greenhouse experiments have shown that root-associated bacteria have beneficial effects on grapevine growth; however, these effects have not been tested in the field. Here, we aimed to demonstrate whether bacteria of different geographical origins derived from different crop plants can colonize grapevine to gain a beneficial outcome for the plant leading to promote growth at the field scale. Methods To link the ecological functions of bacteria to the promotion of plant growth, we sorted fifteen bacterial strains from a larger isolate collection to study in vitro Plant Growth Promoting (PGP) traits. We analysed the ability of these strains to colonise the root tissues of grapevine and Arabidopsis using greenfluorescent-protein-labelled strain derivatives and a cultivation independent approach. We assessed the ability of two subsets randomly chosen from the 15 selected strains to promote grapevine growth in two field-scale experiments in north and central Italy over two years. Parameters of plant vigour were measured during the vegetative season in de novo grafted vine cuttings and adult productive plants inoculated with the bacterial strains. Results Beneficial bacteria rapidly and intimately colonized the rhizoplane and the root system of grapevine. In the field, plants inoculated with bacteria isolated from grapevine roots out-performed untreated plants. In both the tested vineyards, bacteria-promotion effects largely rely in the formation of an extended epigeal system endowed of longer shoots with larger diameters and more nodes than non-inoculated plants.Conclusions PGP bacteria isolated in the laboratory can be successfully used to promote growth of grapevines in the field. The resulting larger canopy potentially increased the photosynthetic surface of the grapevine, promoting growth.

Rotundone is an oxygenated sesquiterpene belonging to the family of guaianes, giving the 'peppery' aroma to white and black pepper and to red wines. Here we describe a novel, convenient protocol for the synthesis of rotundone, starting from a commercially available compound and requiring only two reaction steps, and an improved, faster method of GC separation (30 min) with selective quantisation of rotundone using tandem mass spectrometry in multiple reaction monitoring (MRM) mode with d(5)-rotundone as internal standard. With limits of detection (LODs) of 1.5 ng/L in white wine and 2.0 ng/L in red wine, intraday repeatability CV values of 6% and 5% at 50 ng/L and 500 ng/L and interday repeatability CV values of 13% and 6% at 50 ng/L and 500 ng/L, respectively, the improved protocol provides the desired sensitivity and selectivity for routine analysis of rotundone in both white and red wines. Initial application of this method highlighted the presence of unexpectedly high concentrations of rotundone, thus explaining the origin of the distinctive peppery aroma in Schioppettino and Vespolina red wines and in Gruener Veltliner white wines.