Despite the economic importance and the diffusion of grapevine cultivation worldwide, little is known about leaf chemical composition. We characterized the phenolic composition of Nebbiolo, Barbera, Pinot noir, Cabernet Sauvignon, Grenache, and Shiraz ( Vitis vinifera L.) healthy leaves (separating blades and veins) during the season. Quantitative and qualitative differences were found between leaf sectors and among genotypes. In healthy grapevine leaves, anthocyanins, dihydromyricetin-rhamnoside, hexosides of dihydroquercetin, and dihydrokaempferol exclusively accumulated in veins. Astilbin was the only flavanonol detected in blades and the prevalent flavanonol in veins. Barbera distinguished for the lowest proanthocyanidin and the highest hydroxycinnamate content, and Pinot noir for the absence of acylated-anthocyanins. Nebbiolo, and Cabernet Sauvignon displayed a high concentration of epigallocatechin gallate in veins. Nebbiolo leaves showed the highest concentrations of flavanonols and the widest profile differentiation. Knowledge derived from the present work is a contribution to find out leaf polyphenol potential as a part of grapevine defense mechanisms and to dissect genotype-related susceptibility to pathogens; moreover, it represents a starting point for future deepening about grapevine and vineyard byproducts as a source of bioactive phenolic compounds.

We identified and quantified the main constitutive polyphenolic compounds of the leaves of seven Vitis species and of one interspecific cross, analysing leaf blades and veins separately, to spread light on the strategic localization of polyphenols in leaf tissues. To the best to our knowledge, the main leaf constitutive polyphenols of V. candicans, V. coignetiae, V. vinifera sylvestris and Börner were never described. V. riparia and V. rupestris (belonging to the same botanical series of Ripariae) displayed similar flavan-3-ol and dimeric proanthocyanidin concentration and similar percentage incidence of caftaric acid over total phenolic acids. V. riparia distinguished respect to the other genotypes for its high flavonol content, the highest percentage incidence of myricetin derivatives and an important diversification in the type of accumulated flavonol. V. berlandieri (series Cinereae) and Börner (hybrid of V. riparia x V. cinerea) accumulated low amounts of flavonol-glucosides comparing to the other species, but they showed a wide profile diversification, as well. However, it was V. v. sylvestris, the wild ancestor of Vitis vinifera subsp. sativa that displayed the widest flavonol profile diversification. The differences in the flavonol profile could be related to the genus Vitis evolution: in fact, with domestication, the flavonoid biosynthetic pathway underwent a progressive simplification; for this, the highest flavonol diversity found in Vitis v. sylvestris is probably a demonstration of its reduced or nil level of domestication. V. amurensis, known for its cold tolerance and resistance to downy mildew, anthracnose and white rot, markedly differentiated respect to the other genotypes, for its high concentration of polyphenols, particularly of vein flavonols and flavanonols. Moreover, V. amurensis leaves generally presented a constantly high concentration of constitutive polyphenols throughout the season that probably contributes to protect against adverse environmental condition. The abundance of polyphenols in V. amurensis leaves emphasizes that this species is a source of natural bioactive compounds that could find application for nutraceutical and pharmacological uses. V. berlandieri and Börner markedly distinguished respect to the other studied species for their exclusive capability to accumulate flavones (mainly orientin, isoorientin, vitexin and isovitexin) in blades and in veins, in considerable amounts.Knowledge about these subjects could contribute to shed light on the identification of speciesrelated molecules involved in the plant-defense mechanisms, to the chemotaxonomy of the genus Vitis, to the possibility of identifying specific natural bioactive compounds to use in plant-based preparation for nutraceutical, cosmetic, feed/food-additive purposes.

The first serious outbreak of Flavescence dorée (FD) in Piedmont (North-West Italy) dates back to 1998 in the Tortona area (Alessandria province). FD is a serious quarantine-worthy disease transmitted by the leafhopper Scaphoideus titanus Ball. Different Vitis vinifera L. biotypes react differently to the phytoplasma, in particular as to the accumulation of polyphenols in leaves. In this experimentation, we observed and described concentration and accumulation of the main classes of polyphenols in entire leaves and in leaf blades and veins of two varieties, Nebbiolo and Barbera, displaying different levels of susceptibility to FD. Their well-known different reactions could be related, at least partially, to leaf polyphenols, both as to concentrations and profiles. Nebbiolo displayed some specific traits: i) the higher percentage of incidence over totals of individual molecules known to be powerful antioxidants (caftaric acid over coutaric acid; quercetin glycosides over other flavonols); ii) the higher concentration of flavanols in veins with respect to Barbera and their wider profile (astilbin and a taxifolin-glycoside, this last accumulating exclusively in Nebbiolo).