Generation of alien chromosome addition lines from synthetic Brassica napus: morphology, cytology, fertility and chromosome transmission.
The chromosome complement of B. oleracea (2n = 18) was dissected by means of alien chromosome addition lines generated by successive backcrosses of either of the two B. campestris accessions Chinese cabbage or turnip rape (2n = 20) to the resynthesized B. napus Hakuran (cabbage × Chinese cabbage) (2n = 38). Alien chromosome addition lines were characterized by chromosome counts, morphology, pollen and seed fertility, and transmission of chromosome-specific markers. Mean chromosome number in the BC1 generation was approximately 23.5 and was little influenced by the B. campestris accession. Fertility and isoenzyme marker transmission were also not affected by choice of B. campestris accession. Transmission of chromosome-specific markers to the BC2 was more variable than to the BC1 and appeared to be affected by the B. campestris recurrent accession. Twenty-five monosomic addition lines (2n = 21) were recovered in the BC2 generation, representing 7 of the 9 B. oleracea synteny groups. One monosomic alien chromosome decreased seed fertility but not pollen fertility. Only one monosomic addition line could be reliably identified morphologically.