Agro-Morphological and Cytogenetic Characterization of Hibiscus Genetic Resources: Implications for Germplasm Conservation and Interspecific Breeding

Plant genetic resources are vital for crop improvement, ecological resilience, and agrobiodiversity conservation, making their characterization through morphological and cytogenetic methods essential for breeding and germplasm management. This study comparatively analyzed two herbaceous cultivars Hibiscus moscheutos cv. ‘Carousel Jolly Heart’ and cv. ‘Carousel Pink Passion’ and two woody cultivars, Hibiscus syriacus cv. ‘Sukim’ and cv. ‘Freedom’, to assess interspecific diversity and hybridization potential. Morphological assessments revealed notable differences in flower size and leaf shape between species, with ‘Carousel Pink Passion’ exhibiting the largest flower diameter (16.70 cm) and ‘Freedom’ exhibiting the smallest (10.20 cm). Chromosome analysis confirmed diploidy (2n = 38) in H. moscheutos and polyploidy (2n = 84) in H. syriacus, highlighting a fundamental genomic distinction between the two species. Fluorescence in situ hybridization (FISH) consistently identified two 5S rDNA loci across all cultivars; however, species-specific variation in 18S rDNA loci was detected with four loci in H. syriacus and six in H. moscheutos, suggesting divergent rDNA evolution and distinct genomic organization in the two species. Flow cytometry confirmed significant differences in nuclear DNA content corresponding to ploidy levels: ‘Carousel Jolly Heart’ and ‘Carousel Pink Passion’ measured 2.06 pg and 2.05 pg, respectively, while ‘Sukim’ and ‘Freedom’ measured 4.18 pg and 4.27 pg, respectively.