Introduction The melon (Cucumis melo L., 2n = 24), a species in the Cucurbitaceae family, exhibits extensive diversity. It is a significant horticultural crop in Iran, known for its considerable morphological and agronomic variation. A comprehensive understanding of phenotypic variation is essential for enhancing breeding efficiency and optimizing trait selection. Evaluation of distinctness, uniformity, and stability (DUS) is mandatory prior to cultivar release to ensure the protection of intellectual property rights for newly developed varieties. In addition, comprehensive morphological evaluation is necessary to identify the distinguishing traits of each cultivar. To enhance varietal identification and genetic improvement of melon cultivars, this study investigates their Distinctness, Uniformity, and Stability (DUS) characterization and morphological variation. The present study undertakes an investigation into the Distinctness, Uniformity, and Stability (DUS) characterization, alongside the morphological variation of melon cultivars, to facilitate both varietal identification and genetic advancement. Materials and Methods: The experiment was conducted at the Seed and Plant Certification and Registration Institute (SPCRI), Agricultural Research Education and Extension Organization (AREEO) in Karaj, Iran, during the spring and summer seasons of 2024/2025, employing a complete randomized block design with two replications. This study undertakes a detailed examination of the modified Distinctness, Uniformity, and Stability (DUS) morphological characteristics of forty-two melon hybrid cultivars. It employs both quantitative and visual traits to identify commercially relevant biological differences and to improve the efficiency of breeding programs. A modified descriptive term list from UPOV (The International Union for the Protection of New Varieties of Plants) was utilized to investigate five quantitative and twelve qualitative and pseudo-quantitative traits across various organs, including plant, leaf, flower, fruit, and seed qualities. The DUS (Distinctness, Uniformity, and Stability) test was designed to identify, classify, and safeguard commercial cultivars exhibiting specific superior characteristics. Pearson correlation analysis was performed to determine the interrelationships among the various DUS traits. A specialized TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) algorithm, specifically the Mahalanobis-TOPSIS variant, was developed to establish a comprehensive multi-criteria decision-making model. The breeding potential of forty-two hybrid melon cultivars was assessed and ranked using this model. Results Significant variations in fruit morphology, including color, length, surface, dots, patches, grooves, and flesh, as well as seed characteristics such as color and shape, were observed, enabling effective cultivar differentiation. A pooled Analysis of Variance (ANOVA) over two years revealed significant differences among cultivars (p < 0.05), indicating diverse morphological forms within the studied cultivars. Based on the Distinctness, Uniformity, and Stability (DUS) features of the investigated melon cultivars, the modified DUS trait dataset, specifically fruit warts and the position of maximum fruit diameter, showed no variance across all commercial melon cultivars. A pairwise examination of Pearson correlation coefficients for the six quantitative Distinctness, Uniformity, and Stability (DUS) testing traits revealed that some traits were largely independent, while others were grouped due to strong positive or negative significant correlations. Correlation analysis revealed the highest positive correlation between fruit length with fruit length/width (r=0.86), and the highest negative correlation between fruit flesh diameter with seed length (r=-0.43). Utilizing the M-TOPSIS multidimensional evaluation model, five cultivars—Pooya, Sivano, Derak, Sakura, and Karoun—were identified as exhibiting excellent comprehensive performance based on four economic DUS traits (fruit traits). Significantly, the superior plants demonstrated synergistic advantages across multiple key traits, rather than extreme performance in a single trait. This provides essential materials and a basis for multi-trait synergistic optimization in the collaborative breeding of the evaluated traits in C. melo. Conclusion This study highlights the significant genetic diversity within commercial hybrid melons and identifies critical traits for cultivar differentiation. These results offer actionable insights that can assist breeders in developing superior cultivars with improved yields and traits that satisfy consumer preferences. Furthermore, this study supports ongoing plant breeding initiatives by identifying reliable morphological traits for cultivar differentiation, thereby aiding the enhancement of crop quality and yield. Additionally, it suggests that future research should focus on refining DUS criteria through the inclusion of more traits that effectively distinguish between different melon cultivars. |