Affecting yield components and grape composition through manipulations of the source-sink balance

Manipulation of the source-sink balance in the grapevine through cultural practices such as winter or summer pruning is a long-to-date investigated subject. Though, more recent findings have disclosed the possibility that some specific and targeted operations can be profitably used to pilot the dynamic of ripening, induce desired grape composition and replace other costly manual interventions. The best case in point is leaf removal that when applied pre-flowering (i.e., well ahead of traditional usage scheduled between fruit set and veraison) has proven to be effective under a wide range of cultivars and environmental conditions to control yield by reducing fruit set and/or berry size, induce looser cluster less susceptible to bunch rot and promote ripening as a result of increased availability of assimilate per unit of crop post-veraison. This operation can be fully mechanized and, if needed, replaced by the use of anti-transpirants, i.e., a different tool to impose the required source limitation. A more recent example of a physiological use of leaf removal is given by later (post-veraison), apical-to-the-cluster leaf removal, using a leaf plucker machine which opens a ‘window’ in the upper two-thirds of the vine canopy. When applied in environments where, under the pressure of global warming, over-fast ripening and unbalanced grape composition is becoming quite a common feature, the technique is viable to slow down the sugaring process, retain higher acidity and, at the same time, total anthocyanins and phenolics do not seem to be either delayed or reduced. The most recent research line on the subject is represented by reverting to a very late winter spur pruning with the aim of delaying the annual cycle so that the final stage of ripening occurs in a cooler period.