Field applications of auxin postpone berry ripening in grapevine by altering hormonal dynamics and gene expression

Climate change and rising temperatures exert significant influence on viticulture by advancing phenological progression and accelerating berry development. These shifts result in modifications to grape chemical composition and are often associated with a decline in fruit quality parameters. Auxin hormones are well known modulators of berry maturation, and their application during pre-veraison period has been shown to delay ripening. However, the molecular mechanisms underlying this delay remain largely unexplored. This study applied an exogenous auxin to Chardonnay and Corvina grape clusters during pre-veraison period, leading to a significant delay in ripening development. Key ripening parameters, including total soluble solids, berry weight, pH, and total acidity, were indeed postponed in both varieties following the treatment. Hormonal profiling revealed a delay in the accumulation of the two indole-3-acetic acid (IAA) conjugated forms. A delay in the accumulation of free abscisic acid (ABA) and ABA-glucosyl ester during the veraison interval was also observed. Gene expression analysis aligned with the measurements of technological parameters and hormones concentration demonstrating a delay in the induction of key ripening-associated transcription factors. This study provides insights into the molecular regulation of ripening onset in grape berries recommending auxin application as a potential tool for mitigating the effects of climate change on the acceleration of grapevine phenology.