Abstract Background Crimson Seedless is a globally important table grape cultivar valued for its color, marketability, and nutritional quality. However, enhancing berry coloration and biochemical quality remains a major challenge, especially under fluctuating environmental conditions. In this context, the individual application of nanoparticles or molasses as natural organic stimulants may offer an effective. This study hypothesizes that foliar application of zinc oxide nanoparticles (ZnO NPs) and molasses, either individually or in combination, would increase yield, berry coloration, and antioxidant-related biochemical parameters compared with those of the untreated control. The experiment included eight treatments applied to five grapevines per treatment via a randomized complete block design (RCBD) over two consecutive seasons (2023–2024), and the effects of ZnO NPs at 10, 50, and 100 mg L − 1 , applied alone or in combination with molasses at 1.5 cm³ L − 1 , on productivity, cluster traits, anthocyanin accumulation, and antioxidant-related enzymes were evaluated. Results In terms of productivity, cluster quality, and berry coloration, the treatment with ZnO NPs plus molasses followed closely by ZnO NPs alone surpassed the nontreated vines. The 10 mg L − 1 ZnO NPs + molasses treatment was superior for most of the studied parameters. For example, the total yield increased by approximately 8.9–11.4%, the total soluble solid (TSS) content increased by 48.4–43.8%, the firmness increased by 8.1–12.0%, and the acidity decreased by 16.3–15.4% compared with those of the control treatment in both seasons. Additionally, the same treatment resulted in the greatest increase in anthocyanin content (104.3–73.4%) and PAL activity (48.4–58.1%) compared with those of the control in both seasons. Conclusion The application of 10 mg L -1 ZnO NPs + 1.5 cm 3 L -1 molasses once at the veraison stage increased the grape yield, color, and biochemical quality. While a single-stage application was effective, further studies could explore multistage applications or alternative timings to optimize the results. Graphical Abstract
Samaan et al. (2026) studied this question.