Background and Aims Regulated deficit irrigation (RDI) and bunch thinning are two viticultural practices applied worldwide. There is limited knowledge, however, about their combined effects on carbohydrate dynamics and accumulation. We evaluated during year 3 and 4 of the experiment the effect of 4 consecutive years of RDI and bunch thinning on carbohydrate status, vegetative and reproductive variables. Methods and Results From 2006/07 to 2009/10, we imposed four levels of water supply [100, 60, 38 and 25% of reference evapotranspiration (ETo)] and two crop loads (100 and 50% of the bunches). We compared shoot length, flowers per inflorescence and yield in 2009/10. We also measured pruning mass and the concentration of non‐structural carbohydrates in dormant wood in the winters of 2009 and 2010. Starch concentration in the trunk was reduced by severe water deficit (25 and 38% ETo) and improved by bunch thinning. Pruning mass, shoot length, flowers per inflorescence and yield were affected in vines with water applied at 25 and 38% of ETo. Conclusions Severe water stress and high crop load reduced trunk starch concentration with no interaction between both factors, whereas the concentration of total non‐structural carbohydrate was not affected. Vegetative growth and yield were reduced after 4 years of severe water stress. Significance of the Study We provide evidence that starch concentration and carbon partitioning can be manipulated through common viticultural practices, such as irrigation and crop load.

Background and Aims Regulated deficit irrigation and crop load adjustment are viticultural practices used to improve grape and wine composition. Our objective was to evaluate the combined effect of irrigation and crop load levels on leaf photosynthesis, accumulation of non‐structural carbohydrates and leaf carbon utilisation during the season. Methods and Results The trial started in 2006 in a Vitis vinifera L. Malbec vineyard in Mendoza. Two irrigation levels (100% and 25% of reference evapotranspiration) and two crop loads (20 and 10 bunches per vine, set at veraison) were studied. During the 2009/10 season, diurnal dynamics of leaf water potential, photosynthesis and carbohydrate concentration were determined at anthesis, veraison and harvest. Deficit irrigation reduced leaf starch concentration at veraison and increased soluble sugars. High‐crop load reduced leaf starch concentration at veraison. Starch turnover was correlated with photosynthesis during the previous day. Conclusions Deficit irrigation had a greater effect on carbon allocation between soluble sugars and starch than on total carbohydrate production. Effects of deficit irrigation and crop load operated independently. Significance of the Study This experiment improved our knowledge of carbon assimilation and allocation during the season, which may assist the development of management practices to stabilise yield and fruit composition.