Production of Brassica tri-genomic vegetable germplasm by hybridisation between tuber mustard (Brassica juncea) and red cabbage (B. oleracea)

Brassica is a key agricultural genus, containing oilseed and vegetable crops sharing three major genomes (A, B and C) distributed in diploid (genome: AA, BB and CC) and allotetraploid (genome: AABB, AACC and BBCC) species. Interspecific hybridisation between Brassica species is an important way to combine valuable characters of different species. In the present study, interspecific hybrids between tuber mustard (AABB) and red cabbage (CC) were obtained with the aid of embryo culture. The results showed that ovules at five different maturity levels (7, 9, 10, 13 and 14 days after pollination), which were cultured on Murashige and Skoog medium supplemented with 3 % sucrose, 0.2 % active carbon and 400 mg/L glutamine, showed varying seed survival rates. A total of 15 (5 %) seeds were obtained, with ovules cultured at 14 days after pollination yielding the most seeds. Subsequently, eight (53 %) of the seeds did not germinate into normal plants. Furthermore, the putative hybrids were confirmed by random amplified polymorphic DNA (RAPD) and flow cytometry analysis, and only one (14 %) of the seven plants was confirmed to be a true tri-genomic hybrid (genome: ABC). Then the nodal segments of the true hybrid were treated with liquid medium supplemented with colchicine to obtain an allohexaploid, as confirmed by flow cytometry analysis and morphological observation. The synthesized hybrid showed unique phenotypes in comparison with the parents, such as in stem colour and leaf margin. The synthesized Brassica tri-genomic vegetable germplasm with A, B and C genomes has potential as a source of new crops for agriculture as well as a basis for further investigation of the mechanisms of Brassica evolution and adaptation.