Cytogenetic comparison of Hibiscus syriacus with Hibiscus moscheutos by FISH and flow cytometry

Determination of chromosome number, nuclear DNA content, genome size, and ploidy level as well as information on cytogenetic characteristics are all prerequisite in modern plant breeding. The high number, small size, and similar morphology of mitotic chromosomes in Hibiscus species make it challenging to identify individual chromosomes. The goal of the study was to ascertain the chromosome number, number of 5S and 18S rDNA signals, as well as genome sizes, 2C-DNA content of H. syriacus and H. moscheutos. Two cultivars from each species ‘Shintaeyang’ and ‘Blue Bird’ for H. syriacus and ‘Luna White’ and ‘Luna Pink Swirl’ for H. moscheutos were selected for analyses. The root tip squash method was used to check the chromosomal numbers. The number of chromosomes we found were 84 for H. syriacus and 38 for H. moscheutos. 5S rDNA and 18S rDNA signals were detected by fluorescence in situ hybridization (FISH). H. syriacus and H. moscheutos had two 5S rDNA signals whereas four 18S rDNA were found in H. syriacus and six 18S signals were detected in H. moscheutos. The lengths of mitotic metaphase chromosomes ranged from 2.01 to 7.43 µm and 2.43 to 7.11 µm for H. syriacus ‘Shintaeyang’ and ‘Blue Bird’ respectively, and 2.91 to 5.23 µm and 2.21 to 5.47 µm for H. moscheutos ‘Luna White’ and ‘Luna Pink Swirl’ accordingly. The 2C-DNA content of H. syriacus was 4.02 and 4.18 pg, for ‘Blue Bird’ and ‘Shintaeyang’, respectively, whereas, H. moscheutos had nearly half and that amount was 2.06 and 2.04 pg for ‘Luna White’ and ‘Luna Pink Swirl’, respectively. These findings will contribute to the detailed cytogenetic assessment of Hibiscus and thus benefit plant breeding in this genus.