Grafting is widely used in watermelon production to improve stress tolerance and fruit quality. However, traditional methods retain rootstock meristems, leading to shoot regrowth that increases labor costs and transplant expenses. Cotyledon-less splice grafting removes these meristems and prevents regrowth, but survival rates decline sharply because cotyledons normally supply hormones and carbohydrates during healing. Successful grafting depends on rapid callus formation, vascular reconnection, and balanced hormone–sugar signaling. Although light intensity is known to influence seedling vigor and metabolism, its molecular role in graft union healing remains poorly understood. Based on these challenges, deeper research into how light regulates graft healing mechanisms is urgently needed.
Researchers from Huazhong Agricultural University and collaborating institutions reported (DOI: 10.1093/hr/uhaf293) on February 2026 in Horticulture Research that pre-grafting exposure to high light intensity (300 μmol·m⁻²·s⁻¹) significantly improves survival and healing in cotyledon-less watermelon grafts. Using integrated transcriptomic and metabolomic profiling, the team uncovered how light-driven changes in hormone signaling, carbohydrate allocation, and phenylpropanoid pathways promote vascular reconnection and tissue adhesion, providing molecular insight into an optimized grafting strategy.
By cultivating rootstock seedlings under higher light intensity before grafting, survival rates of cotyledon-less grafts increased from below 20% to nearly 98%. Importantly, the light treatment applied to rootstocks—not scions—proved decisive. High-light rootstocks showed stronger adhesion force, faster phloem and xylem reconnection, and enhanced root regeneration during early healing.
Metabolomic profiling identified elevated levels of auxin and cytokinin derivatives, sugars such as D-galactose and galactinol, and phenylpropanoid intermediates including cinnamic acid and m-coumaric acid. These metabolites support energy supply, hormone-mediated cell division, and lignin deposition—key processes for graft stabilization.Transcriptome analysis revealed strong enrichment in plant hormone signal transduction, starch and sucrose metabolism, and phenylpropanoid biosynthesis pathways. Grafting-related genes such as PXY, WOX4, NAC086, CALS7, and TMO6 were significantly upregulated under high light conditions, coordinating cambium activation, cell wall remodeling, and vascular differentiation. Weighted gene co-expression network analysis further identified key regulatory modules tightly correlated with survival rate, adhesion strength, and vascular reconnection.Together, these molecular and metabolic shifts form an integrated regulatory network driving rapid graft union formation under optimal light conditions.
“Our findings show that light is not merely an environmental factor but a central regulator of graft healing,” said the corresponding researcher. “By enhancing carbohydrate accumulation and activating hormone signaling before grafting, high light prepares the rootstock for rapid vascular reconnection. This coordinated transcriptional and metabolic reprogramming enables cotyledon-less grafts to overcome carbon starvation stress and establish stronger unions. The approach offers a physiological and molecular basis for improving grafting efficiency in controlled-environment agriculture.”
The study provides a practical strategy for commercial nurseries seeking to adopt cotyledon-less grafting while minimizing labor costs linked to rootstock regrowth. Optimizing pre-grafting light intensity in plant factories with artificial lighting can enhance early healing efficiency, ensuring robust seedling establishment and potentially improving downstream yield and fruit quality. Beyond watermelon, the findings may inform grafting practices in other cucurbit and vegetable crops. By linking environmental control with molecular regulation, this work bridges controlled-environment agriculture and functional genomics, offering a scalable pathway toward more efficient, high-quality grafted transplant production.
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References
DOI
10.1093/hr/uhaf293
Original Source URL
https://doi.org/10.1093/hr/uhaf293
Funding information
This work was supported by National Natural Science Foundation of China (32573012; 31972434), China Agriculture Research System of MOF and MORA (CARS-25), Young Scientist Fostering Funds for the Notional Key Laboratory for Germplasm Innovation and Utilization of Horticultural Crops (11909920008), Hubei Provincial Key Research and Development Program (2023BBB033; 2024EIA009), Fundamental Research Funds for the Central Universities (2662024JC004), and the Innovation fund of Guangdong Academy of Agricultural Sciences (202208).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.