Nutritional implications of water stress in grapevine and modifications of mechanical properties of berries.

Deficit irrigation may be used to control canopy development, yield, and fruit composition in order to enhance fruit colour, texture, and juice composition. The present study was carried out in 2007 using five-year old Lambrusco grapevines grown with the root system split into two pots. Water stress was applied on half of the vines (stressed) by withholding water from one out of the two pots from pre-veraison till harvest. At harvest, yield and cluster number per vine were recorded. Leaves and berries were collected and their mineral composition analyzed. Samples of 200-berries were collected to obtain qualitative parameters and to investigate mechanical properties using a TAxT2i Texture Analyzer. In order to confirm berry skin values obtained using texture analysis, microscope observations were made on frozen samples. Berry development (cluster and berry weight) was reduced by water stress; yield, sugar concentration, acidity and pH were similar between treatments, while malic acid and potassium concentrations in control vines were greater than in stressed vines. Water stress significantly enhanced the total anthocyanins. Mechanical properties of berries were strongly affected by water stress, showing a significant increase of berry skin thickness and a decrease of firmness. Microscope observations confirmed greater skin thickness as a result of water stress. Calcium, Mg, and B content in leaves and in berries significantly changed when water stress conditions were imposed. Sulphur and Mn content in leaves and P content in berries were also affected by treatment. These changes probably resulted from differential uptake and flow of nutrients from leaves to berries under water stress. In particular low Ca in leaves and high Ca levels in berries were registered in stressed vines, indicating the important role of Ca in enhancing berry skin thickness. The same pattern of flow from leaves to berries was noticed for Mg. In contrast, low levels of B were found both in leaves and in berries of stressed plants.