Eggplant Rootstock Grafting Enhances Tomato Fruit Sweetness and Nutritional Value via Metabolic Reprogramming

Small tomatoes are an important economic fruit crop. Strategies to rapidly and stably improve their taste and nutritional quality are of significant economic value. This study evaluated grafting tomato scion ZheYingFen1 (ZYF1) onto eggplant rootstocks (ZheQie117 or ZheQie10). Comprehensive metabolomics and targeted assays demonstrated that grafting substantially increased fructose and glucose levels, thereby enhancing sweetness compared with self-rooted controls. Lycopene content rose significantly, particularly with the ZQ117 rootstock, without elevating key organic acids linked to sourness. Conversely, most free amino acids decreased, including umami-associated glutamate. Energy metabolite profiling showed graft-specific shifts, with pronounced enrichment in sulfur-containing glucosinolate biosynthesis pathways, suggesting modified defense responses and flavor profiles. These results demonstrate that compatible eggplant rootstocks provide a practical horticultural strategy to directly improve tomato sweetness and nutritional value without compromising acidity. This work provides evidence that eggplant rootstocks can effectively improve both the sweetness and nutritional value of tomatoes through metabolic reprogramming, offering a practical and sustainable approach for quality enhancement in commercial tomato production while maintaining a favorable acidity balance.