Production of allohexaploid Brassica hybrid between tuber mustard (Brassica juncea L. var. crassicaulis Chen &Yang) and Chinese kale (Brassica oleracea var. alboglabra Bailey)

Abstract

Brassica is a key agricultural genus, containing oilseed and vegetable crops, which includes three major genomes (A, B and C), distributed in diploid (genomes: AA, BB and CC) and allotetraploid species (genomes: AABB, AACC and BBCC). Interspecific hybridization between Brassica species is an important way to combine valuable characters from the different species. In the present study, distant hybridization between inbred lines of tuber mustard (Brassica juncea var. crassicaulis Chen &Yang; AABB) and Chinese kale (Brassica oleracea var. alboglabra Bailey; CC) was conducted and allotriploid interspecific hybrids were identified. The hybrid seed set was improved by gibberellin treatment of the stigmas prior to pollination. Eight hybrid seedlings were obtained by bud pollination and ovary culture, and all seedlings were confirmed to be true hybrids by phenotypic analysis, cytological observation (27 chromosomes) and the use of parent-specific randomly amplified polymorphic DNA (RAPD) molecular markers. After tissue culture and colchicine-induced chromosome-doubling treatment, allohexaploid hybrids (AABBCC) were isolated and identified from the eight hybrids. The chromosomes of five plants were completely doubled, with a doubling rate of 5.68 %, and the number of chimeric plants was 24, at a rate of 27.27 %, when roots were immersed in 0.1 % colchicine solution. In comparison with the allotriploid hybrid, the synthetic hexaploid hybrids showed unique phenotypes with normal anthers, well-developed pods, larger flowers and petals, thicker stems than either parent and other phenotype types intermediate between the two parents. In the present study, synthetic tri-genomic Brassica vegetable germplasm, combining the A, B and C genomes, was created for use in vegetable breeding, as well as for a basis for further investigation of the mechanisms of Brassica evolution and adaptation. The current study is of great significance for the use of these allohexaploid plants to explore the heterotic effects of distant hybridization and for genetic improvement.