Cytokinin–Ethylene Crosstalk Mediates Bottle Gourd Rootstock-Induced Vigor in Grafted Melon

Grafting is a pivotal horticultural technique for enhancing vegetable crop productivity; however, the specific molecular mechanisms governing rootstock-induced vigor remain insufficiently elucidated. This study deciphers how bottle gourd rootstock augments growth in melon scions through an integrated approach combining physiology, transcriptomics, phytohormone profiling, and functional genetics. Phenotypic analysis confirmed a significant increase in plant height, fresh weight, and stem diameter in heterografted scions compared to controls. Transcriptome sequencing of scion apices identified 663 core differentially expressed genes (DEGs) specifically modulated by the bottle gourd rootstock. These DEGs were prominently enriched in carbohydrate metabolism and plant hormone signal transduction pathways. Consistent with this, hormonal assays revealed a specific elevation in cytokinin and ethylene levels in the scion, accompanied by the upregulation of key pathway genes, including <i>MELO3C016881</i> (<i>LOG</i>) and <i>MELO3C007769</i> (<i>ERF060</i>). Crucially, virus-induced gene silencing of either gene completely abolished the rootstock-conferred growth advantage. Our findings preliminarily unveil the secret behind scion vigor, providing a foundational mechanistic framework for how rootstocks reprogram scion development. The identified genes, <i>MELO3C016881</i> and <i>MELO3C007769</i>, offer direct molecular targets for the precision breeding of superior scions in melon.