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

Authors: Sakhanokho, Hamidou; ISLAM-FARIDI, NURUL - Us Forest Service (FS); Babiker, Ebrahiem; NELSON, CHADRLES - Us Forest Service (FS); Stringer, Stephen; Adamczyk, John

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2019
Publication Date: 1/20/2020
Citation: Sakhanokho, H.F., Islam-Faridi, N., Babiker, E.M., Nelson, C., Stringer, S.J., Adamczyk Jr, J.J. 2020. Determination of nuclear DNA content, ploidy, and FISH location of ribosomal DNA in Hibiscus hamabo. Scientia Horticulturae. 264:109167. https://doi.org/10.1016/j.scienta.2019.109167.
DOI: https://doi.org/10.1016/j.scienta.2019.109167

Interpretive Summary: Hibiscus hamabo is a deciduous salt-tolerant shrub or tree with golden yellow flowers that is grown for its fibers and ornamental value. Because the plant grows well in in habitats with high salt concentrations, it is considered one of the best afforestation trees used in reclamation programs in urban and coastal areas high in salt content. However, very little is known about its genetics, so we determined some of its genetic characteristics including genome size, number of chromosomes, and ribosomal DNA localization. Our results help understand the basic genetics of H. hamabo. Also, these results will be useful for future basic and applied research on this hibiscus species. Tolerance to abiotic stresses (salt, drought, moderate cold hardiness) of H. hamabo is an attractive and desired trait; however, improving floral longevity, number, and frequency will be necessary to increase its ornamental value. Our results, especially the determination of the chromosome number, lays the groundwork for an efficient hybridization scheme aimed at improving these traits in new hybrid selections.

Technical Abstract: 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.