G. BARBEAU, R. MORLAT, C. ASSELIN, A. JACQUET et C. PINARD
Unité de Recherches sur la Vigne et le Vin (URVV), Centre INRA,
42 Georges Morel, 49071 Beaucouzé Cedex (France)
Abstract : In the framework of a research programme on the terroirs in viticulture, a red of experimental plots was established in the Loire Valley area in 1978 with the Cabernet Franc variety. In 1988, eleven of those plots were given an intensive follow-up, with special emphasis on the phenological stages, the growth and development of the vegetative apparatus and the composition of the grapes at harvest time. After a few years, we can consider that 1988 was an average year for the last fifteen vintages, both on the climatic side and on the wine quality side. Therefore it seems to be justified to use the data of that particular year to study the terroir effect on the composition of the grapes. The results show important differences between terroirs in terms of precocity of the phenological stages, stems growth, setting of the leaf area, vigour and productivity of the plants. These differences are found also during the maturity process and at harvest time ; sugars, organic acids, anthocyanins and polyphenols are concerned. An index for measuring the precocity of the grapevine cycle on each terroir is used to compare the terroirs and to establish relationships with the composition of the grapes at harvest time. Through the analysis of the data, it is possible to distinguish two groups of factors which determine the behaviour of grapevine in a given terroir. The first one is related to the precocity of the cycle of the plant ; it influences the quality of the grapes at harvest time. The second is related to the vigour ; it is linked to the productivity of the plants.and the acidity of the must. The level of development of the primary leaf area at flowering time seems to play an important role in relation with the composition of the grapes in sugars, organic acids and anthocyanins ; the earlier the flowering, the better the relationship.
Key words : grapevine, terroir , Loire Valley, precocity, quality of harvested grapes