STERILITY IN SUCCESSIVE BACKCROSSES OF RAPHANOBRASSICA (2N=4X=36) WITH RECURRENT BRASSICA-OLERACEA (2N=2X=18)

A series of crosses to develop cytoplasmic male sterility in the cole crops by transferring the B. oleracea L. (2n = 18) genome into the cytoplasm of radish (Raphanus sativus L., 2n = 18) through the amphidiploid Raphanobrassica (2n = 4x = 36) was terminated because of complete seed sterility of the only 2 BC6 [backcross] hybrid plants obtained. There was no improvement of seed set in 6 backcrosses to diploid B. oleracea, and the chromosome numbers of the few plants producing seeds were higher than expected, frequently being close to the triploid number (2n = 3x = 27) of the BC1. Zygotes with < 2 radish chromosomes were not found; those with < 4 were few; and those with < 6 rarely produced offspring.