Effects of Four Pumpkin Type Grafting Rootstocks on the Fruit Development, Quality, and Metabolomics of Melon Cultivar Mingzhu 5

Purpose The application of melon grafting technology is constrained by challenges including scion-rootstock incompatibility and a tendency for fruit quality to decline. The aim of this study was to investigate the effects of pumpkin rootstocks on the fruit growth, quality, and metabolomics of the melon cultivar Mingzhu 5, to screen for superior rootstocks and elucidate the underlying metabolic mechanisms of their effects.

Methods The scion Mingzhu 5 was grafted onto four pumpkin type rootstocks (Heiba No.1, Jinjiazhen, Japanese cedar, and Zhenxi 316), with self-rooted seedlings serving as the control. The single melon weight, flesh thickness, soluble solids content, and fruit texture were measured. Untargeted metabolomics analysis was performed on flesh samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Combined with multivariate statistical analysis and pathway enrichment analysis, the metabolic pathway alterations were investigated.

Results The Zhenxi 316 graft combination performed best, showing significant increases in single fruit weight and flesh thickness compared to the control, without negative impacts on fruit shape index or soluble solid content. However, all four grafting combinations were accompanied by increased hardness in mouthfeel, accumulation of bitter compounds, and a reduction in characteristic aroma volatiles. Metabolomics analysis identified 84 significantly differentially expressed metabolites, mainly enriched in 20 metabolic pathways, such as β-alanine metabolism, biosynthesis of phenylpropanoids, pantothenate, and CoA biosynthesis, which were closely associated with plant stress resistance and the regulation of fruit flavor.

Conclusion Although grafting with Zhenxi 316 as the rootstock results in a decline in fruit flavor quality for Mingzhu 5, it has no adverse effects on the fruit shape index or center-soluble solids content. Therefore, Zhenxi 316 is a potential rootstock suitable for Mingzhu 5. Grafting modulates a broad metabolic network in the fruit flesh, enhancing plant stress resistance while simultaneously altering the accumulation of metabolites related to texture, bitterness, and aroma, ultimately leading to changes in fruit flavor. This study provides a theoretical basis for selecting superior melon rootstocks and managing grafting-related quality traits.