Karyotype and nuclear DNA content analyses of Korean native Hibiscus 'Gangneung' and 'Baekryungdo' using fluorescence in situ hybridization and flow cytometry

Determination of nuclear DNA content, genome size, ploidy degree as well as prior knowledge on cytogenetic properties are prerequisites for modern plant breeding. The objectives of this study were to determine (1) 2C-DNA contents, genome sizes, and ploidy degree, (2) number of chromosomes, (3) 5S and 18S rDNA loci distribution, and 4) karyomorphology of two Korean native cultivars of Hibiscus 'Gangneung' and 'Baekryungdo'. According to the flow cytometry results, the 2C-DNA contents of both 'Gangneung' and 'Baekryungdo' were nearly identical, with 2.14 pg and 2.18 pg respectively. Additionally, putative DNA content were 2091.32 Mbp and 2135.00 Mbp for 'Gangneung' and 'Baekryungdo' respectively. In this study, we determined that H. syriacus 'Gangneung' had 84 chromosomes, whereas 'Baekryungdo' had 90. We detected 5S rDNA and 18S rDNA loci through fluorescence in situ hybridization (FISH) technique. FISH results showed one pair of 5S rDNA loci in both cultivars, whereas two and three pairs of 18S rDNA loci were detected in 'Gangneung' and 'Baekryungdo', respectively. In 'Gangneung,' the 5S rDNA loci pair was detected in the short arm of chromosome #22, whereas in 'Baekryungdo,' the 5S loci was found in the centromere of chromosome #7. Furthermore, one 18S rDNA pair was found on the long arm of chromosome #14 and another pair on the short arm of chromosome #20 in 'Gangneung'. Two pairs were found in the long arms of chromosome #11 and #20 for 'Baekryungdo,' while the last pair was found in the short arm of chromosome #45. The somatic chromosome' length in 'Gangneung' and 'Baekryungdo' ranged from 2.10 to 7.31 mu m and from 2.21 to 6.85 mu m, respectively. To the best of our knowledge, this study is the first cytogenetic report of Korea native 'Gangneung' and 'Baekryungdo' cultivars. These findings will contribute to the detailed cytogenetic assessment of both the 'Gangneung' and 'Baekryungdo' cultivars and benefit plant breeding within this genus.

Automated summary

In this study, the nuclear DNA content, genome size, ploidy degree, and cytogenetic properties of two Korean native cultivars of Hibiscus 'Gangneung' and 'Baekryungdo' were determined. The flow cytometry results showed that the 2C-DNA contents of both cultivars were nearly identical. Fluorescence in situ hybridization (FISH) technique revealed the presence of 5S and 18S rDNA loci in both cultivars. This cytogenetic assessment of the cultivars will contribute to plant breeding within this genus.