Karyotype and genomic in situ hybridization pattern in ×Brassicoraphanus, an intergeneric hybrid between Brassica campestris ssp. pekinensis and Raphanus sativus

The karyotype and genomic in situ hybridization (GISH) of an intergeneric hybrid Baemoochae, ×Brassicoraphanus, which originated from hybridization between Chinese cabbage, Brassica campestris (synonym, rapa) ssp. pekinensis, and radish, Raphanus sativus, were analyzed to determine its chromosome complement. In the karyotype analysis, B. campestris was verified to have 2n = 20 chromosomes, including a particular pair of the subtelomeric chromosomes with the nucleolar organizer; R. sativus to have 2n = 18 chromosomes, including a particular pair of the submetacentric chromosomes with the secondary constriction of nucleolar organizer; and ×Brassicoraphanus to have 2n = 38 chromosomes, including both the subtelomeric chromosomes of Brassica and the secondary constriction chromosome pair of Raphanus. These findings indicate that ×Brassicoraphanus is a polyploid between Brassica and Raphanus. In the GISH analysis using chromosomes of B. campestris and R. sativus as the probe and blocking DNA, respectively, only 20 chromosomes of Brassica had hybridization signals. This result reveals that ×Brassicoraphanus is an intergeneric hybrid consisting of the complete genomes of both Brassica and Raphanus. However, the nucleolar organizers of Brassica and Raphanus were not identified because the hybridization signals appeared to be centering mainly around the centromere, becoming weak at the edges.