Development of Brassica rapa-nigra monosomic alien addition lines: cytology, genetics, and morphology.

Brassica rapa-nigra monosomic alien addition lines (MAALs) were developed and compared with B. oleracea-nigra MAALs containing the same B-genome chromosomes. The diploid Brassica nigra (black mustard) is the donor of the B-genome for two allotetraploids: B. juncea (AABB) and B. carinata (BBCC). To dissect the B-genome of B. nigra within the A-genome background of B. rapa, the progenies of resynthesized B. juncea, successively pollinated by the parental B. rapa, were screened using cytological methods and molecular markers. Seven out of eight B. rapa-nigra MAALs (2n = 21, AA + 1B) were obtained, except for the AA-B6 MAAL. The additional chromosome appeared as one univalent in 86.76% of pollen mother cells and formed one trivalent with two A-genome chromosomes in 13.24% of cells. Different alien B-genome chromosomes were transmitted to progeny at varying rates, with higher transmission rates via female gametes (averaging 13.59%) than via male gametes (7.31%). These MAALs exhibited significant phenotypic variations which were either of parental origins or novel traits, and chromosomal locations of some traits from B. nigra or genetic interactions were realized from the joint results of B. rapa-nigra and B. oleracea-nigra MAALs with the same additional B-subgenome chromosomes. Comparison analyses of these two sets of MAALs provided new insights into the genetic interplay of the B-genome with A- and C-genomes in these two allotetraploids.