Elevating Berry Excellence: GABA-Induced Stimulation of Anthocyanin Biosynthesis and Antioxidant Defense in Flame Seedless Grapes

The grapevine ( Vitis vinifera L.) stands as one of the most important fruit crops due to its high nutritional value, palatability and economic significance. In order to mitigate the harmful effects of climate change on fruit quality, primarily the berry colouration and antioxidant potential, the present study was conducted to investigate the potential of foliar application of γ-aminobutyric acid (GABA) during two consecutive cropping seasons on grape cv. Flame Seedless. At the onset of veraison, 17-year-old vines were sprayed with GABA @ 25, 50 and 100 mM. The results revealed that GABA @100 mM significantly improved total phenolic content and antioxidants, remaining statistically comparable with GABA @50 mM. Fruit colour was also favourably influenced, as it produced higher a* and lower b* values, improving berry appearance. Moreover, it also improved the cluster and berry physical traits by recording the highest cluster length, width and weight, along with increased berry size, berry weight and yield. Antioxidant enzymes, including catalase (CAT), phenylalanine ammonia-lyase (PAL) and superoxide dismutase (SOD), were significantly elevated under all treatments, with 50 and 100 mM concentrations exhibiting the strongest responses. GABA @50 mM recorded the highest TSS, lowest L* values and maximum total anthocyanin content, followed closely by 100 mM. Overall, pre-harvest foliar GABA @ 50–100 mM offers great potential to enhance grape productivity, quality, adaptability, precision nutrient use, deficit irrigation efficiency, eco-friendly cultivation and premium export.