The climate has changed. Let’s change viticulture!

Apertura_portaleFor a long time the wine sector has been confronted with extreme climate events, which anticipate the ripening of the grapes and alter their characteristics, often bringing about the production of either little balanced wines or products with excessive content in alcohol. In order to better understand this phenomenon and face these distortions, a group of researchers coordinated by Alberto Palliotti of Dipartimento di Scienze Agrarie, Alimentari e Ambientali (Department of Agriculture, Food and Environment) of the University of Perugia (Umbria) tried to define some guidelines which can update the cultivation techniques in the vineyard.

The context of this research

Which need did your review begin from?
“The research line which was the object of this review was born to coincide with the onset of new and unexpected problems started in the warmest summer of the last few centuries, namely the one of the year 2003. Since that summer, the cultivation systems applied to the vine, although optimized and considered as effective, have begun to show some macroscopic abnormalities in many growing areas, both in phenology and ripening process of grapes. A strategy for the medium-long term will have certainly to provide an upgrade for the ampelographic platform, especially as regards vines, clones, and rootstocks which result to be resistant to abiotic stresses, scarcity of water, and excesses, first of all thermal and radiative ones. At the same time, it will be necessary to broaden the knowledge, especially as for vines of the territory, concerning the mechanisms with which they adapt themselves to variable conditions in terms of radiation, temperature, deficit of vapour pressure, and water availability, as well as the possibility of optimizing the use of water resource”.

What does the market ask for?

Do the current market requirements harmonize with cultivation systems which are by now well established?
“Currently the markets, both domestic and foreign ones, are more and more demanding wines characterized by moderate alcohol content without penalizing, in red wines, intensity and shades of colour, structure, and sensory properties, and at the same time guaranteeing, in white wines, the preservation of a sufficient acidic and aromatic outline. The success of today’s lighter style is witnessed by the increase in both demand and consumption of such wines of this category as: Mosel Riesling, Vinho Verde, Prosecco, Asti, rosé wines, and some Italian light red wines produced with such widely cultivated vines as Sangiovese, Montepulciano, Ciliegiolo, Lambrusco, Dolcetto, etc. On the other hand, as a matter of fact high alcohol contents, if they are not carefully balanced, weigh down the wine, making it little fresh and difficult to drink, with excessive and persistent effects in terms of heating and sweating. Therefore, it emerges how one of the traditionally pursued objectives in all the viticultural areas over the world, that is to say the production of grapes with high sugar content, has deeply changed”.

How is it possible to adapt?
“The production patterns of wines with moderate alcohol content can certainly harmonize with the present cultivation systems, with some technical devices. For example, in the warm and dry years it is necessary to limit the excessive dehydration of the grapes, because the reduction of water content in the must is followed by a concentration of sugars, and therefore the predisposition to excessive alcohol content is accentuated. In such cases, it is necessary to avoid topping, desuckering, and excessive defoliation, trying instead regrouping the foliage, guaranteeing adequate production for a single vine, that is to say not too scanty, and control the physiology of the foliage”.

And what about the training systems?
“Some problems have recently emerged as for systems in vertical wall, that is to say trellis, which have been the preferred solution for the Italian vineyards in recent years. Surveys conducted in wine-growing areas all over the world, where the problem of thermal and light stresses is emerging in all its importance, showed that the ideal microclimate for both black and white grapes is a system of prevailing diffuse light, interrupted by flashes of light which penetrate into the canopy from different directions. This structure is easily achieved by setting free foliage with erect posture of the vegetation, such as a revisited small tree, or, in a more modern version, the system with free cordon. On the other hand, the trellis involves the problem of over-exposure and overheating of grapes during the hottest hours of the day”.

Damages, remedies, and changes of direction

So, are problems of ripening systemic?
“In recent decades, the effects of climate change have occurred worldwide, especially in terms of progressive increase in air temperatures during the growing season. One of the most evident reactions of Vitis vinifera to rising temperatures is the shortening as for the duration of phenological stages which, however, occur with a considerable advance in comparison with past times. In particular, the last stages of ripening often coincide with very warm days. A direct consequence of this phenomenon is usually a too rapid and excessive accumulation of sugars, often associated with low levels of acidity caused by a rapid degradation of the organic acids in the must, high pH, and atypical aromas. Therefore, the resulting wine is too alcoholic, little fresh, characterized by unbalanced aromatic component and exposed to stability and preservation problems”.

And what about viticulture at high altitudes?
“In the wine sector, the search for excellence at high altitudes is one of the future bets. In mountain areas and in the foothills, the choices concerning both exposure of soils and their altimetric elevation might be reconsidered. 30-40 years ago it was preferable to choose southern and not too high exposures in order to guarantee the heating requirements of a variety and allow full maturation of grapes, but today it might be appropriate to choose exposures which bring about a lower interception of solar radiation and / or place the vineyards at slightly higher altitudes”.

 

(in box)

Possible actions concerning cultivation

The cultivation techniques, both traditional and innovative ones, which can be used now for limiting the effects induced by climate changes, are shown in the table. Alberto Palliotti underlines: “In my opinion, the techniques belonging to 3rd and 4th groups, in spite of their undeniable relevance for the contribution they provided for the widening of basic knowledge, are difficult to apply in practice, because they combine high cost to rather uncertain results in the vineyard. The cultivation techniques included in the 1st and 2nd groups are more reliable, because they are characterized by ease of execution, reasonable costs, and guarantee of success. The mechanisms which allow the success of these techniques are quite solid and are mainly based on containing in targeted way the available content in carbohydrates for the accumulation in the must through two main ways: 1) induction of mechanisms of nutritional competition among the different organs of the vine during the ripening of the grapes; 2) induction of photosynthetic stresses, measured in the post-veraison stage“.

 

1 Cultivation techniques based on the induction of mechanisms of nutritional competition among the different organs of the vine Calibrated increase in unitary yield obtained by increasing the number of buds; late topping of buds; late irrigations; late winter pruning
2 Cultivation techniques based on the induction of calibrated photosynthetic stresses Late defoliation in the post-veraison stage; shading of foliage with shielding sheets; use of substances with antiperspirant activity in the post-veraison stage
3 Cultivation techniques based on the use of products which act on the processes of grape ripening Synthetic auxins; brassinazole; salicylic acid; synthetic cytokinins; inhibitors of ethylene and compounds which release ethylene
4 Alternative cultivation techniques Early harvest of part of the pending production for the realization of specific oenological products

(article by Alessandro Battaglia Parodi)

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