Physiological behavior of the Chasselas grape variety under water deficit: 30 years of experiments in Switzerland

Abstract

In the context of increasingly hot and dry summers, the adoption of innovative irrigation technologies has become essential for maintaining grape production while minimizing water use. Grapevines exposed to water and thermal stress activate adaptive mechanisms that, while protective, negatively impact yield and quality. Intense solar radiation further exacerbates these challenges, impairing the phenolic composition of grapes and causing berry sunburn, which compromises yield and fruit quality. To address these issues, a cooling system was developed to reduce sunburn damage in grape clusters. The system integrates proximal sensors to monitor vineyard microclimatic conditions and an actuator that activates nebulizers when temperatures exceed 35 °C, a critical threshold for maintaining biochemical compound stability and preventing berry damage.

Field trials conducted in 2022–2023 at the University of Bologna’s experimental vineyard on Pignoletto white cultivar, investigated two treatments: Defoliation (NO DEF vs. DEF, applied pre-veraison) and Misting (NO FOG vs. FOG). The study assessed their effects on yield, berry necrosis, and secondary metabolites such as flavonols and aroma compounds.

The application of nebulized water in the fruit zone consistently reduced air and berry temperatures during both trial seasons. This cooling effect significantly mitigated sunburn damage, increased cluster weight, and enhanced overall productivity in mist-treated vines. While technological maturity showed no significant differences between the two treatments, misted vines exhibited a trend toward higher acidity during the markedly hot 2023 season.

Flavonol synthesis was unaffected by the cooling effect but was stimulated by increased light exposure, resulting in higher concentrations in defoliated treatments. Preliminary findings also highlight the cooling system’s critical role in preserving aroma compounds, vital for grape and wine quality.

In conclusion, the fruit-zone cooling system proves to be a valuable and sustainable strategy to alleviate the adverse effects of summer stresses, particularly by reducing sunburn damage and improving yield and fruit quality in white berry Pignoletto cultivar.