Interspecific hybridization is a fundamental strategy in ornamental plant breeding, which enables the combination of desirable traits. In Lilium, complex hybrids, including longiflorum-Asiatic (LA) and Oriental-Trumpet (OT) cultivars, have been extensively developed via interspecific crosses between distantly related genome groups. However, the genomic structure and chromosomal behavior of these commercially important hybrids are largely uncharacterized. In this study, we applied genomic in situ hybridization (GISH) to eight triploid LA and OT lily cultivars to evaluate their chromosomal composition, assess their genome stability, and explore the utility of GISH as a practical cultivar verification tool. Flow cytometry and somatic chromosome counting confirmed the triploid status (2n = 3x = 36) of all the assessed cultivars. GISH analysis also revealed distinct parental chromosome sets in the background of each hybrid, with no evidence of intergenomic translocations or recombination. The LA cultivars exhibited 12 chromosomes derived from L. longiflorum and 24 from Asiatic parents, whereas the OT cultivars demonstrated 12 chromosomes of Oriental hybrid origin and 24 derived from Trumpet hybrids. This consistent non-recombinant genomic structure across all the cultivars strongly supports somatic polyploidization as the primary mechanism underlying their development. The suppression of homoeologous recombination underscores the cytogenetic stability of these hybrids and supports their clonal maintenance through vegetative propagation. Furthermore, these findings validate GISH as an effective tool for cultivar verification and chromosomal assessment in ornamental plant breeding and reinforce the importance of cytogenetic profiling for the development and management of interspecific hybrids.

Introduction
Materials and Methods
    Morphological Trait Analysis
    Plant Materials and Preparation of SomaticChromosomes
    Ploidy Analysis
    Genomic DNA Extraction and Probe Labeling
    Genomic In Situ Hybridization (GISH)
Results
    Phenotypic Characteristics Analysis
    Ploidy Analysis
    GISH and Karyotype Analysis
Discussion
Conclusion
Acknowledgments
References

• Eun-Jae Seo(Department of Horticultural Science, Kyungpook National University, Daegu 41566, Korea)
• Yun-Jae Ahn(Department of Horticultural Science, Kyungpook National University, Daegu 41566, Korea, Institute of Agricultural Science and Technology, Kyungpook National University, Daegu 41566, Korea) Corresponding author
• Ki-Byung Lim(Department of Horticultural Science, Kyungpook National University, Daegu 41566, Korea, Institute of Agricultural Science and Technology, Kyungpook National University, Daegu 41566, Korea, World Horti Center, Kyungpook National University, Sangju 37224, Korea)