Effects of different winter pruning times on table grape vines performance and starch reserves to face climate changes

In the context of climate change, in which some extreme weather and climate events have increased in frequency and intensity because of global warming, adaptive techniques in viticulture have become necessary to reduce the resulting negative impacts. This study on four table grape cultivars has evaluated the effects of different winter pruning treatments (time of pruning) on phenology, fruit composition and starch content in canes and ≥two-year-old wood. By shifting the pruning time from leaf fall up to budbreak (BBCH 08), a neutral response on yield and berry quality parameters (TSS, TA and pH) was observed for the 4 cultivars. Late pruning treatments resulted in shorter shoot lengths and delayed phenological stages for the early ripening cultivars. The partitioning of starch between canes and older wood was almost similar, although lower in canes, with average values of 13% and a significant reduction at budbreak in order to release soluble sugars for the initial vegetative growth. Starch was mainly located in newly formed xylem, i.e., in the parenchymatic rays where amyloplasts are located, whereas a smaller amount of starch was visible in the other tissues (phloem, cortex). The possibility of a late pruning until over budbreak can be considered a practice to avoid some late spring frost risks, often occurring in viticultural areas. Thus, a ‘precise’ application of winter pruning into a global warming viticulture context could have potential benefits, performing a cost-effective tool management without negative (or very limited for early cultivars) effects on yield and quality of table grapes.