Exogenous γ-aminobutyric acid application delays onset of ripening in Grenache, Chardonnay, and Shiraz grape berries.

Physiological and biochemical changes in Vitis vinifera L. (grape) berries during development have been extensively studied; however, the role of γ-aminobutyric acid (GABA), a non-protein amino acid that changes during berry development, remains unknown. We hypothesized that GABA accumulation in the berry may have an osmoprotective role and increase the living tissue percentage during development. On this precedent, exogenous application of GABA (5 mM) to bunches may result in a delayed onset of ripening. GABA was observed to accumulate concomitantly with sugar accumulation commencing at veraison in Chardonnay, Shiraz, and Grenache grape berries sampled from the Coombe vineyard over two seasons (2018-20). Cultivar-dependent variability was noted in hydrogen peroxide and antioxidant capacity. In berries treated with exogenous GABA (5 mM) weekly from the pea-stage until veraison, decreases in berry mass, total soluble solids, and cell death, along with increased antioxidant capacity, and a delay in veraison were observed. These findings suggest that exogenous GABA may modulate ripening, although the exact mechanisms require further investigation. Elucidating these mechanisms may benefit growers by improving grape berry quality and enabling modification of ripening in response to a changing climate or adverse weather events.