Vol. 9, Special Issue 11, Part O (2025)

Quantifying genetic divergence is fundamental for exploiting heterosis and broadening the genetic base in onion (Allium cepa L.) breeding. In the present investigation, eighteen short-day onion genotypes were assessed using Mahalanobis D² statistics to characterize multivariate diversity and define genetic relationships. Tocher’s clustering grouped the genotypes into six distinct clusters, reflecting wide genetic dispersion, while the occurrence of two monotypic clusters highlighted the presence of uniquely differentiated genotypes within the population. The maximum inter-cluster distance observed between Cluster I and Cluster III (D² = 10,657.99; D = 103.24) indicated exceptionally strong genetic contrast, suggesting that crosses between these clusters would yield maximum heterotic potential. Similarly, substantial divergence among other cluster pairs, such as I-IV and III-VI, further emphasized the breadth of available genetic variability. Trait contribution analysis revealed that yield-associated and bulb architectural traits accounted for more than 92% of the total divergence, confirming their dominant influence on multivariate separation. The relatively low contributions of quality and stress-response traits suggest their lesser role in defining major divergence patterns, although they remain relevant for targeted improvement. Overall, the study demonstrates the presence of strong, structured genetic diversity among the evaluated onion genotypes. The markedly high D² values and differentiated cluster composition provide valuable guidance for selecting genetically distant parents, enabling breeders to design crosses that maximize heterosis, generate wide segregation, and accelerate genetic progress in onion improvement under short-day environments.