Origin of new Brassica types from a single intergeneric hybrid between B. rapa and Orychophragmus violaceus by rapid chromosome evolution and introgression

Many novel lines were established from an intergeneric mixoploid between Brassica rapa (2n = 20) and Orychophragmus violaceus (2n = 24) through successive selections for fertility and viability. Pedigrees of individual F₂ plants were advanced to the 10th generation by selfing. Their breeding habit was self-compatible and different from the self-incompatibility of their female parent B. rapa, and these lines were reproductively isolated to different degrees from B. rapa and B. napus. The lines with high productivity showed not only a wide spectrum of phenotypes but also obvious variations in fatty acid profiles of seed oil and glucosinolate contents in seed meal. These lines had 2n = 36, 37, 38, 39 and 40, with 2n = 38 being most frequent (64.56%), and no intact O. violaceus chromosomes were detected by genomic in situ hybridization (GISH) analysis. Amplified fragment length polymorphism (AFLP) analyses revealed a high extent of variation in genomic compositions across all the lines. O. violaceus-specific bands, deleted bands in B. rapa and novel bands for two parents were detected in these lines, with novel bands being the most frequent. The morphological and genetic divergence of these novel types derived from a single hybrid is probably due to rapid chromosomal evolution and introgression, and provides new genetic resources for rapeseed breeding.