Chromosomal characterization of a potential model mini-Citrus (Fortunella hindsii)

Mini-Citrus Fortunella hindsii (Hongkong kumquat), a member of the Rutaceae family, has the potential to be a model citrus due to its unique botanical features, including small plant size and short juvenility. However, data on its chromosomal characteristics, including karyotype and chromosomal homology, is lacking. Our research further investigates the chromosomal features of four Fortunella genotypes, F. crassifolia (JG), F. hindsii (PE1, PE2, and ME1), using chromosomal karyotyping, chromomycin A3(CMA) staining, 45S rDNA FISH, and hierarchical cluster analysis. The results showed high diversity of both CMA banding patterns and 45S rDNA physical mapping among these four genotypes. Based on chromosome ideograms, it was found that chromosomes of polyembryonic JG, PE1, and PE2 were heterozygous, while chromosomes of monoembryonic ME1 were homozygous. CMA band-based cluster analysis showed that all four Fortunella genotypes belonged to a single group, distinct from other Citrus genotypes. This work suggests that homozygous monoembryonic F. hindsii (ME1) is suitable for future development into a model plant for Citrus genetic and functional genomics research.