Cytological and pollen fertility analysis of diploids and triploids in Korean Disporum species

The genus Disporum (Colchicaceae) comprises approximately 20 species distributed throughout Asia, of which four species (Disporum sessile, D. smilacinum, D. uniflorum, and D. viridescens) are currently recognized in Korea. Mixed-ploidy variations, including odd-ploidy levels within the same species, are important in evolution as they enable backcrosses with their parental cytotypes. However, Korean Disporum species have not been examined in detail with regard to ploidy variation and pollen fertility. Therefore, we document the occurrence of diploids and triploids among the Disporum spp. in Korea and report for the first time that D. sessile and D. smilacinum are both diploid (2n = 2x = 16) and triploid (2n = 3x = 24), though they were previously known as diploids from Korean natural populations. The total haploid chromosome length is variable, ranging from 67.32 µm in diploid D. smilacinum to 108.11 µm in triploid D. smilacinum; however, the karyotypes of the investigated species are similar regardless of the ploidy levels. The occurrence of fertile pollen grains from triploid individuals is approximately two-thirds that from diploid species, but triploid plants show no pollen tube germination compared to their diploid counterparts. Overall, this study presents the first comprehensive chromosomal and pollen fertility data for Korean Disporum species, and thus lays the foundation for better understanding the evolution and diversification of morphologically and cytologically variable plant groups.