Influenza dell’esposizione del vigneto sulla maturazione dell’uva

[English version below]

Lo studio è stato condotto in vigneti commerciali di Vitis vinifera cv Nebbiolo localizzati in Piemonte, Italia del Nord-Ovest, intorno alla sommità di una collina. L’obiettivo dello studio è stato di determinare come l’esposizione del vigneto possa influenzare il comportamento vegetativo della vite, il manifestarsi delle fasi fenologiche, e la cinetica di maturazione dell’uva con particolare riguardo all’accumulo di antociani e flavonoli. Le esposizioni più meridionali hanno indotto precocità di germogliamento e fioritura ma diminuzione della fertilità per gemma e, di conseguenza, della resa per pianta influenzando anche il peso dei grappoli, degli acini e delle bucce; hanno promosso una maggiore concentrazione dei solidi solubili nelle ultime fasi di maturazione ma la sintesi degli antociani e dei flavonoli ha subito un rallentamento durante le fasi tardive di maturazione. L’esposizione occidentale ha favorito il ritardo delle fasi fenologiche e un aumento della fertilità per gemma, del peso del grappolo e della resa produttiva, determinando un minore accumulo di solidi solubili nel mosto ma una maggiore sintesi di antociani. Si è evidenziata, in oltre, una probabile influenza della temperatura non solo sulla sintesi degli antociani ma anche dei flavonoli delle bucce.

The study was conducted in Sinio (Piedmont, Northwest Italy) in commercial vineyards of Vitis vinifera cv. Nebbiolo, situated on the top of a 30 % slope hillside, thus they were differently exposed: two of these (A) was exposed to South, another (B) to East-South-East, the fourth (C) to West-North-West. The clone CVT 141 grafted onto 420 A, was cultivated in every vineyard. Vines were VSP trained and pruned to the Guyot system (10 bud cane plus 2 bud spur). Vine theoretical density was 5200 vine/ha. The aim of this study was to determine how the vineyard exposition influences vine vegetative behaviour, phenological phase timing, grape ripening kinetic and grape properties including colour and flavonols. The results were used to characterize the vineyards in a sort of farm zoning, helping to choose the best technical management.
The 2009 vintage was characterized by a very rainy winter and spring, and a very hot summer (from mid July until the beginning of September the maximum temperature, as average, exceeded 32 °C). Bud burst and flowering resulted delayed in C, respect to A and B vineyards, whereas bud fertility was higher in C. That fact induced a higher bunch weight (313 g) in vineyard facing West (C), respect to those Southward (A and D) where bunch weight was similar (224 g) also thanks to a higher berry mass (1.87 g in A and D, 2.09 g in B, and 2.07 g in C). Furthermore, vineyard exposition influenced the vine vigour and yield that in C and D were twice that in A and B vineyards. Soluble solid content at harvest appeared higher in A, B and D (24.3 Brix as average) than in C vineyard (23.7 Brix). Southern expositions (A and D) delayed the beginning of veraison and reduced the anthocyanin concentration at harvest (600 mg/kg) respect to B (670 mg/kg) and C (770 mg/k); further differences among vineyards were observed both in the pattern of flavonol accumulation and in their concentration at harvest. In synthesis the Southern expositions advanced the phenological phases and decreased bud fertility, yield per vine and weight of bunches, berries and berry skins. In addition, it promoted a high concentration of soluble solids at harvest but not of anthocyanins whose concentration slowed down during the late phases of ripening. Western exposition (C) promoted a delay of phenological phases, and an increase of bud fertility, bunch weight and yield per vine; it induced a medium accumulation of soluble solids but the highest synthesis of anthocyanins. Due to the global warming we can expect a high variability between vintages from a weather point of view. We think that a sort of farm zoning matched with data obtained from observations executed in successive vintages could be a useful help to choose the best technical management for a specific year and to foresee in advance the vintage results.