Deficit irrigation in grapevine improves water-use efficiency while controlling vigour and production quality Chaves M.M.1,2 (firstname.lastname@example.org), Souza C.R.2,4, Santos T.P.1,2, Rodrigues M.L.1, Lopes C.M.1, Maroco J.P.2,3, Pereira J.S.1 1 Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, Portugal 2 Laboratório de Ecofisiologia Molecular, Instituto de Tecnologia Química e Biológica, Avenida da República, Apartado 127, 2780-901 Oeiras, Portugal 3 Instituto Superior de Psicologia Aplicada. Rua Jardim do Tabaco, 34. 1149-047 Lisboa, Portugal 4 Laboratório de Sementes e Fisiologia Vegetal. EMBRAPA SEMI-ÁRIDO Drought is one of the most important factors limiting crop yield and quality, worldwide, especially in regions with climate of the Mediterranean–type. In these regions, viticulturists rely on irrigation water during drought periods. However, there is considerable controversy concerning the positive and negative effects of grapevine irrigation regarding growth as well as must and wine quality. On the other hand, with enhanced pressure on water resources, the increasing demand for vineyard irrigation will only be met if there is an improvement in the efficiency of water use. This goal can be obtained by several ways, deficit drip-irrigation practices being the most widely used to save water and simultaneously improve wine quality. We studied different irrigation regimes in two grapevine varieties (Moscatel and Castelão), during three years. The treatments were full irrigation or minimum water deficit (FI, 100% of the Etc), deficit irrigated (DI, 50% of the Etc, half of water supplied to each side of the row), partial root drying (PRD, 50% of ETc periodically supplied in alternation, to only one side of the root system whereas the other one wa s allowed to dry) and rainfed, non-irrigated grapevines (NI). The results showed that deficit irrigation treatments (50% Etc) promoted an increase in water use efficiency (WUE) as compared to full irrigation, either in the short-term, as expressed by the A/gs ratio or in the long-term shown by the increase in 13C in the plant tissues, especially the berries. For most of the season, deficit irrigation treatments (PRD and DI) had no negative impact on CO 2 assimilation, despite less water application than in full-irrigation, although they generally showed a larger relative stomatal limitation (RSL). This is in accordance with the observed higher WUE. Our results also showed a stability of the photosynthetic machinery in grapevines under low-to-moderate water availabilities, as demonstrated by the maintenance of the activity of three Calvin Cycle enzymes and of the V cmax values. However, a decline in Jmax was observed in NI vines, that can be a result either of a decrease in ATP production or, alternatively of decreased mesophyll conductance to CO2 diffusion. A restriction of growth was observed in PRD as compared to DI, suggesting that in PRD a chemical regulation on growth was superimposed on hydraulic signalling, since it showed higher water potential although both received the same amount of water. Berry temperature of the NI and PRD treatments was always higher than in the denser canopies (FI and DI) and this was associated with a higher concentration of anthocyanins and total phenols. No significant differences were observed in yield between the three irrigation treatments even though FI received twice as much water as PRD or DI. It was also apparent that the response to deficit irrigation varied with the grapevine variety and with the environmental conditions of the particular year, differences between treatments being more marked under drier conditions. Differences among varieties may be related to differences in sensitivity of stomata, shoot growth and/or the interaction between rootstock and cultivar to soil water availability.
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