Interploidy hybridization enhances floral phenotypic diversity of Iris × norrisii tetraploids

Interploidy hybridization has been widely utilized in plant breeding and cultivar improvement. In ornamental species, interploidy hybridization between diverse diploid lines and synthetic tetraploids enables the transfer of rich diploid variation to polyploid backgrounds. Although previously applied in the breeding of Irises and other ornamentals, this approach remains insufficiently explored in synthetic polyploid cultivars. To address the limited floral variation observed in artificial tetraploid lines of Iris × norrisii , we performed interploidy crosses between tetraploid plants and both diploid and mixoploid lines. Hybrid progenies were evaluated based on floral traits, chromosome counts, and the meiotic behavior of microspore mother cells in parental plants. Crosses using tetraploid plants as female parents yielded tetraploid or near-tetraploid aneuploid progeny, whereas those with diploid female parents produced only diploid offspring. Cytological analysis revealed meiotic abnormalities in both diploid and tetraploid, contributing to the formation of unreduced male gametes. Interploidy hybrids displayed a broader range of perianth colors than control tetraploid crosses, whereas floral morphological variation was similar between the two groups. These findings demonstrate that diploid I. × norrisii contributes to the diversification of floral traits in tetraploid lines via the transmission of genetic variation through unreduced male gametes. Interploidy hybridization is a promising approach for enhancing phenotypic diversity in polyploid ornamental breeding.