Enhancement of Fruit Technological Maturity and Alteration of the Flavonoid Metabolomic Profile in Merlot (Vitis vinifera L.) by Early Mechanical Leaf Removal

Removal of basal leaves near bloom inevitably affects grapevine balance and cluster microclimate conditions, improving fruit quality. Mechanization of this practice allows growers to save time and resources, but, to our knowledge, has not yet been compared with manual application in a cool climate region where seasonal temperature accumulation frequently limits fruit technological maturity and phenolic ripening in red Vitis vinifera cultivars. In our research, berry sugar concentration was highest in the pre-bloom mechanical treatment (PB-ME). Furthermore, metabolomics analysis revealed that PB-ME favored the accumulation of significantly more di-substituted anthocyanins and flavonols and OH-substituted anthocyanins compared to the manual application. Given that vine balance was similar between treatments, increased ripening in PB-ME is likely due to enhanced microclimate conditions, and higher carbon partitioning through a younger canopy containing basal leaf fragments proximal to fruit. This information provides an important strategy to consistently ripen red Vitis vinifera cultivars in cool climates.