Maintaining canopy density under summer stress conditions retains PSII efficiency and modulates must quality in Cabernet Franc

Shoot topping and other summer grapevine management practices are considered crucial for producing high-quality wine. However, in recent years, climate change is increasing the need to reassess these strategies, as excessive radiation and high temperatures can negatively impact canopy functionality and berry quality. Indeed, it has been hypothesized that limiting summer vegetative pruning may protect the bunch, via shading, and the leaf by maintaining a more favorable environment for leaf functionality (e.g., lower VPD, reduced high light stress) owing to a denser canopy. In this work, a series of canopy manipulation treatments (shoot topping vs. long-shoot bundling; secondary shoot trimming vs. untrimmed) were tested in a replicated factorial block design over two seasons in field-grown grapevine plants (cv. Cabernet Franc grafted in SO4). Overall, treatments in which secondary shoot removal and/or shoot topping were not applied produced a higher canopy area, increased pruning wood and leaf layers, and had a higher Fv/Fm on warm days when compared to pruned canopies. These were associated with a year-dependent modulation of quality parameters of the must in which long-shoot bundling treatment, overall, produced the highest polyphenol and anthocyanin contents and must acidity. Our data provide evidence of a potential usefulness of preserving dense canopies under high temperature – high irradiance conditions with desirable effects on leaf photosynthesis and must quality when long-shoot bundling was applied