Determination of nuclear DNA content, ploidy, and FISH location of ribosomal DNA in Hibiscus hamabo

•Cytomolecular characterization of Hibiscus hamabo was performed.•The 2C value of Hibiscus hamabo was determined to be 4.06 + 0.08 pg (3973.08 + 78.90 Mbp).•Hibiscus hamabo has a chromosome number of 2n = 92.•We observed four loci of 18S and one locus of 5S rDNA, which were located on five different pairs of homologous chromosomes. Hibiscus hamabo Sieb.et Zucc, a deciduous shrub or tree, is an important semi-mangrove plant with golden yellow flowers. The plant is also cultivated for its fiber and grown as an ornamental. It is halophytic and considered one of the best afforestation trees used in reclamation programs in urban and coastal areas high in salt content. However, very little work has been done on its genetics; therefore, this study was undertaken to determine the genome size, the chromosome numbers, and rDNA (18S rDNA and 5S rDNA) loci in H. hamabo using flow cytometry, protoplast spread technique, and oligonucleotide fluorescence in situ hybridization (FISH), respectively. H. hamabo was found to have a 2C-value of 4.06 + 0.08 pg (3973.08 + 78.90 Mbp) and a chromosome number of 2n = 92. We observed four 18S loci and one 5S rDNA locus on five different pairs of homologous chromosomes. The observed FISH signal intensities for the 18S rDNA varied from chromosome to chromosome, indicating that each locus had different rDNA repeat copy numbers. The pericentromeric regions of each chromosome observed were highly heterochromatic. The findings of this study will benefit future cytogenetics and genomic investigations as well as lay the groundwork for more efficient breeding programs aimed at developing improved H. hamabo hybrids.