Karyotype variation and conservation in morphotypes of non-heading Chinese cabbage

Non-heading Chinese cabbage encompasses a wide diversity of morphotypes, like the well-known Pak-choi, Wu ta cai, Cai xin, Tai cai, and Fen nei cai. Despite recent developments in re-sequencing which results in the detection of SNPs, insertions, deletions and copy number variants, there has been no systematical cytogenetic characterization of different non-heading Chinese cabbage morphotypes, aiming to detect large structural variations. To tackle this issue, the karyotypes of five genotypes belonging to five non-heading Chinese cabbage morphotypes were analyzed using fluorescence in situ hybridization (FISH) with ribosomal DNA (rDNA) and blend DAPI band (BDB) on mitotic chromosomes. The ideograms of these five non-heading Chinese cabbage genotypes were produced by exploring and comparing the distributional patterns in terms of rDNA (45S and 5S) and constitutive heterochromatin regions between morphotypes. This study revealed variation in the distributional patterns of ribosomal genes and heterochromatin regions, which point to chromosomal rearrangements in non-heading Chinese cabbage. The 45S rDNA site on chromosome A5 and 5S rDNA signal on chromosome A10 were conserved between all five morphotypes, suggesting that these sites were presented in the ancestor karyotype of non-heading Chinese cabbage. Karyotypic variation and conservation facilitates accurate estimation of the genetic diversity, to better understanding of the evolution, and insight in this variation may facilitate breeding of non-heading Chinese cabbage.