Exploring the relationship between leaf water potential, defoliation, and grape berry physical properties of Merlot (Vitis vinifera L.) grapevine

The aim of this study was to examine the impact of leaf water potential and defoliation treatments on the physical properties of grape berries. The research was conducted over two consecutive years (2019-2020) using ‘Merlot’/41B graft combination grapevines grown in the Chateau Kalpak vineyards located in Tekirdağ, Şarköy. The experiment involved four distinct water stress levels (S0, S1, S2, and S3), which were determined based on leaf water potential measurements. These stress levels were subjected to different irrigation levels. Additionally, defoliation treatments were applied, including Control (C), Full Window (FW), Right Window (RW), and Left Window (LW). The results showed that the effects of water stress and defoliation treatments on berry physical properties were statistically insignificant. However, in the second year of the study, the FW treatment was observed to have led to changes in the desired direction for grapevines. This was likely due to the cumulative decrease in water reserves caused by reduced precipitation over multiple years, making the effects of FW treatment more prominent. Moreover, the study found that both current and past vegetation period conditions influence vine production year, leaf water potentials (Ψleaf), and stress levels. Finally, the data revealed that berry weight and % dry weight increased with higher stress levels.