A study of the chromosome number and genome size of the rare species Rhododendron keiskei var. hypoglaucum in Korea

Rhododendron keiskei var. hypoglaucum (Ericaceae) was recently reported in Korea, with a disjunct distribution on the southern islands of the Korean Peninsula. Although chromosome numbers and ploidy variations are important traits in angiosperms, gaining a clear understanding the cytological features of Rhododendron has been hampered by the small size of its chromosomes. We herein report the chromosome number, karyotype struc-ture, and genome size of R. keiskei var. hypoglaucum for the first time. The chromosome number of the investigated plants was 2n = 26 with x = 13 as the base chromosome number, which is the one of the frequently encountered base chromosome numbers in Rhododen-dron. The karyotype of R. keiskei var. hypoglaucum is composed of metacentric and sub-metacentric chromosomes similar in length, which ranged from 1.39 to 2.40 ??m. The DNA 1C-value in all examined accessions was small, ranging from 0.63 to 0.65 pg, further sup-porting the stable genome size in Rhododendron. These comprehensive cytological results provide a framework for detailed molecular, cytogenetic, and phylogenomic analyses that can be used to interpret the slow species diversification rate in Rhododendron.

Automated summary

This study reports the chromosome number, karyotype structure, and genome size of Rhododendron keiskei var. hypoglaucum for the first time. The chromosome number of this plant was found to be 2n = 26 with x = 13 as the base chromosome number. The karyotype consisted of metacentric and sub-metacentric chromosomes of similar length. These findings provide important insights for further molecular, cytogenetic, and phylogenomic analyses of Rhododendron.