Assessment of the temperature threshold for the occurrence of sunburn damage in Vitis vinifera L. 'Sangiovese'

In the last decades the occurrence of sunburn damage in vineyards has intensified due to climate change, resulting in serious consequences for yield and berry composition. Recognizing the significance of this emerging issue, the present study aimed to assess the temperature threshold causing sunburn damage under different levels of cluster exposure and vine water status. The experiment was conducted in 2021 and 2022 on ‘Sangiovese’ vines, cultivated near Bologna and trained to VSP spur-pruned cordon. Treatments were arranged in a strip-plot design and the main factors were: cluster exposure (leaf removal of the basal leaves at veraison vs. no leaf removal) and irrigation (irrigation from berry softening to the end of August vs. no irrigation). Berry temperature was continuously recorded by thermocouples connected to a WSN, and the evolution of sunburn damage (i.e., necrosis and berry shrivel) was visually estimated every week. Yield parameters and berry composition were assessed at harvest and anthocyanin analysis was conducted by HPLC on frozen berries. In both years, the temperature of the most exposed berries raised over 40°C for more than 40 h, and the combined effect of light incidence and high temperatures caused the appearance of intense sunburn damage. On the other hand, no symptoms were found on the berries shaded by the foliage. Moreover, irrigation mitigated berry temperature, reducing the severity of sunburn damage. The sunburn damage caused by leaf removal lowered cluster weight and, consequently, yield, but irrigation limited both the incidence of symptoms and yield loss. Finally, the concentrations of soluble solids and anthocyanins were lowered by irrigation. The results of this study will be used to develop a warning tech solution that will alert growers to the risk of sunburn damage and suggest management techniques to reduce the impact on the berries.