Increasing drought and soil salinity pose significant threats to crop production around the world. One potential strategy to mitigate the impacts of these environmental changes is grafting, a horticultural technique that joins tissues from different plants. This study aimed to investigate and model changes in the expression of NAC and WRKY genes in grafted watermelon under varying salt and drought stress conditions (mild to extrem). The control groups were not restricted by any limitations. Citrullus lanatus (Thunb.) Matsum. & Nakai (watermelon) was used as the scion, and Lagenaria siceraria (Molina) Standl (bottle gourd) served as the rootstock in our experiments. During the 14-day treatment period, individuals from the grafted watermelon and bottle gourd plants were more successful to maintained water balance and growth rates, while ungrafted plants exhibited growth retardation and tissue damage, especially under salt stress. The analysis of gene expression revealed that grafted plants showed significantly increased expression of salt- and drought-sensitive genes, including ClNAC2b, ClNAC69, ClNAC72, ClWRKY13, ClWRKY14, and ClWRKY23, compared to ungrafted plants under low-stress conditions. These adaptations, such as stomatal closure and regulation of evaporation, enabled the improved grafted plants to respond more effectively to abiotic stress, supporting their survival and normal development. Our findings underscore that grafting is an environmentally friendly, rapid, and effective technique to enhance plant resilience against abiotic stresses, offering promising avenues to improve stable food crop production amidst increasing environmental challenges.

Grafting alters the genetic and anatomical features of plants. Although grafting has been widely applied in plant propagation, the underlying processes that govern the effects of the procedure are not fully understood. Samples were collected to study the long-term influence of grafting on the leaf-shoot morphology, leaf-shoot anatomy, and genetic signature of the grafted plants. Citrulus lanatus (Thunb.) Matsum. & Nakai (cv. Lady) was used as the scion, and Lagenaria siceraria (Molina) Standl (cv. Argentario) as a rootstock. In grafted plants, leaf blades and petioles were 20.92% and 12.82% longer, respectively, while the midrib collenchyma was 35.68% thicker, and the diameter of the vessel member was 11.17% larger than in ungrafted plants. In the stem, grafting affected the arrangement and number of vascular bundles (from 1 to 2 rings). The thickness of the epidermis decreased by 69.79%, and the size of the external fascicular phloem decreased by 23.56%. The diameter of the vessel member of the grafted plants increased by 28.94%. Eight out of ten evaluated primers met the requirements (stability in both watermelons and bottle gourd, tissue-specific). In the genetic tests, we examined whether this change in the gene expression pattern is due to the grafting and, if so, to what extent. Seven out of eight tested Small Auxin Up-Regulated RNA (SAUR) genes were expressed in the ungrafted and grafted C. lanatus lines in four cases; the expression increased by more than 10% after grafting. The morpho-anatomical changes and genetic variation reported in this study for grafted lines of C. lanatus contribute to the understanding of the underlying mechanisms of plant growth observations resulting from grafting.