Effects of nitrogen-doped Graphene Quantum Dots Applications on Yield and Quality in Grape Varieties

Carbon dots (CDs), which have been included in the family of carbon-based nanomaterials since 2004, can be easily prepared from different carbon-based sources and are being tested as fertilizers, micronutrients, nanopesticides, and nanoherbicides with their mechanical, thermal, and chemical properties. Although it is reported that it can improve yield and product quality in different species, studies on its effects on grape varieties are insufficient. In applications, the effects of CDs on plant growth, biochemical content, photosynthesis, and plant yield are examined. Nitrogen-doped graphene quantum dots (N-GQDs) used in this study were produced by dissolving 1 mmol citric acid and 3 mmol urea in 5 mL of water, keeping in the oven at 160 ˚C for 4 h, then adding ethanol and centrifuging at 5000 rpm for 5 min. N-GQDs were applied to cv Ekşi Kara and cv Gök Üzüm at different doses (0, 0.10, 0.25, 0.50, 1 g L-1) by foliar spraying with four replications at four stages approximately (1) week before flowering, (2) at the berry setting stage (when berries reached approximately 2–3 mm in diameter), (3) at the berry coarsening stage (when berry size reached 5–7 mm in diameter), and (4) at the veraison stage The effects of the applications were evaluated by the parameters of cluster and berry sizes, °Brix, pH, titratable acidity (TA), total phenolic content, total antioxidant activity, berry skin colour, berry stemming resistance, berry skin tearing resistance, stomatal conductance, leaf temperature, chlorophyll content, photosynthetic rate in harvested grapes. For all descriptive analyses, analysis of variance (ANOVA), Tukey test, and post-hoc analysis were performed with the statistical packages available in R Studio. Principal Component Analyses (PCAs) with the ggplot2 package and the heatmap produced by the Pheatmap package were used to better understand and depict the correlations between variables. While N-GQDs applications provided improvement in all yield and quality traits examined, the effectiveness of the 0.10 g L-1 dose was more pronounced. Genetic divergence was evident in the effectiveness of the treatments. In PCA analysis, the first two principal components (PC1 and PC2) of the samples in panicle, berry, and leaf datasets explained 41.3% and 18.6% of the variance, respectively. As a result of this study, it was determined that N-GQDs applications improved photosynthesis, yield, and quality parameters and accelerated ripening in two different grape cultivars. In conclusion, 0.10 g L-1 N-GQDs can be tested as a locally produced tool for promoting quality improvement in grape cultivars.