Effects of irrigation and shoot thinning on the size and phenolics content of developing grape berries (Vitis vinifera L. cv. Tempranillo)

Aim of study: The concentration of phenolics in the grape berries can be influenced by cultural practices such as irrigation or thinning. The main objective of the present study was to evaluate the effect of combinations of these practices on grape size and phenolics content. Area of study: The trial was carried out in an experimental cv. Tempranillo vineyard located in Extremadura, Spain. Material and methods: Two irrigation regimes were considered: rainfed vines (non-irrigated, NIr), and 100% ETc irrigated vines (Ir). For each irrigation treatment, two cropping levels were studied: low shoot-thinning (LT) vs high shoot-thinning (HT) implemented in winter and spring, respectively. Berry weight, and total phenolics, proanthocyanidin, and anthocyanin concentrations were determined at eight stages of berry development in three consecutive years (2014, 2015, and 2016). Main results: Specific weather conditions of each year affected phenolics accumulation differently. In 2014, where maximum temperatures were low and an important rainfall occurred at Stage II, both the NIr-LT and NIr-HT treatments led to the greatest concentrations of total phenolics, proanthocyanidins, and anthocyanins. In 2015, where a little rainfall was registered at Stage II, the berries from the NIr-HT and Ir-HT treatments accumulated the greatest total phenolics and proanthocyanidin contents, but the NIr-LT and NIr-HT treatments led to the greatest accumulation of anthocyanins. Finally, in 2016, where high maximum temperatures and scarce rainfall were registered, the Ir-LT and Ir-HT treatments presented the greatest concentrations of total phenolics, proanthocyanidins, and anthocyanins. Research highlights: A significant effect of irrigation and thinning was observed on berry size and phenolic content, as well as year x thinning interaction.