The effects of abscisic acid on grape berry ripening are affected by the timing of treatment

Aims: Grape berry is a model non-climacteric fruit, and many researchers have focused their investigations on its onset of ripening, termed véraison. This process, lasting several days, is composed by many changes, including berry softening, colouring, and sweetening. It is not synchronous for different vines, neither for different clusters on a vine, nor for different berries in a cluster. An important issue for investigations on véraison is : when does exactly this process begin? Which is the main triggering signal? In our work we tried to elucidate how abscisic acid (ABA) treatments affect the shift between green and ripe berries on Cabernet-Sauvignon, through the treatment with ABA and with inhibitors of ABA biosynthesis (fluridone) and degradation (Tetcyclacis), and how the effects of ABA changes are dependent on berry developmental stage. Methods and results: Treatments were done on berries before véraison and at early- and mid-véraison. ABA treatment always increased ABA skin concentration, while fluridone affected it only at the before véraison treatment and tetcyclacis was not effective. ABA and fluridone treatments were effective at modifying skin anthocyanin concentration and, to a lesser extent, skin sugar concentration, in the pre-véraison treatment and not in the other treatments. Conclusion: We conclude that the grape berry is sensitive to ABA in a short time window just before véraison. Significancand impact of study: This has a significant impact on the choice of treatment time in experiments devoted to the study of the triggering signals for ripening in grape berries, and for the understanding of its mechanismof action.