Karyotype diversity of Korean landrace mandarins by CMA banding pattern and rDNA loci

Abstract Mandarin is the major type of citrus grown in Jeju, Korea and has a long history of cultivation there. Landrace Citrus species represent broad and natural genetic variability, which are important and valuable as genetic material. In this study, metaphase chromosomes of six Korean landrace mandarins were analyzed to understand the phylogenetic relationship among them and to compare these characteristics with those of other Citrus species at a cytogenetic level using CMA banding patterns and rDNA loci. Chromosomes were categorized into five types according to the distribution and number of heterochromatic CMA-positive bands; type A chromosomes have two telomeric and one proximal bands, type B have one telomeric and one proximal bands, type C have two telomeric bands, type D have one telomeric band, and type E have no band. Gamza mandarin ( C. benikoji ) displayed the 1A/45S + 2B/45S + 2C + 5D + 1D/45S + 1D/5S-45S + 6E pattern, without a solitary 5S rDNA locus that differentiated the gamza mandarin from other accessions. A solitary 5S rDNA locus was observed in the chromosomes of byungkyul mandarin ( C. platymamma ) (1A/45S + 2B/45S + 1C + 6D + 1D/45S + 1D/5S-45S + 5E + 1E/5S) and cheongkyul mandarin ( C. nippokoreana ) (1A/45S + 1B/45S + 1C + 7D + 1D/5S + 1D/45S + 1D/5S-45S + 5E). The chromosome composition of byungkyul mandarin based on CMA banding pattern and rDNA loci suggests that byungkyul mandarin may be related to pummelo, sweet orange, and members of the Citrus subgenus Papeda during its evolution. Cheongkyul mandarin possessed a distinct marker chromosome (D/45S) that can be used to distinguish cheongkyul madrarin from the other Korean landrace mandarins. Jinkyul mandarin ( C. sunki ) (1A/45S + 1B/45S + 1C + 10D + 2D/5S-45S + 3E) may be related to pummelos. The karyotype of pyunkyul mandarin ( C. tangerina ) (3B/45S + 2C + 7D + 1D/5S-45S + 5E) suggests that the pyunkyul mandarin is a hybrid between C. grandis and C. reticulata . Binkyul mandarin ( C. leiocarpa ) (1A/45S + 1C + 6D + 2D/45S + 2D/5S-45S + 6E) seemed to be related to mandarins and pummelos. Heterozygous karyotypes of six accessions separated and differentiated each of the six Korean landrace mandarins and potential marker chromosomes were identified.