MEIOTIC BEHAVIOR IN INTERGENERIC HYBRIDS BETWEEN BRASSICA-NAPUS AND ORYCHOPHRAGMUS-VIOLACEUS

Meiosis was studied in pollen mother cells (PMCs) with 2n = 31 in the intergeneric hybrid between Brassica napus L. (2n = 38) and Orychophra gmus violaceus (L.) O.E. Schulz (2n = 24). Three patterns of chromosom e behaviour ir ere observed. (I) All 31 chromosomes proceeded directly to the second division, giving rise to unreduced gametes. (II) Two gr oups of 12 and 19 chromosomes moved to opposite poles during the first division and produced. after the second division, four daughter chrom osomal groups: two with 12 chromosomes and two with 19 chromosomes. Ac cordingly, these two types of gametes have the same number of chromoso mes as found in the gametes produced by the two parental species. They probably contain complete chromosome complements of O. violaceus and B. napus, respectively. (III) At anaphase 1, 19 univalents possibly of B. napus origin, moved to the poles in different numbers but most fre quently in a 9:10 distribution. Twelve chromosomes, possibly of O. vio laceus origin, appeared as six bivalents that lagged behind and were n ot included in the telophase I nuclei. The presumable O. violaceus chr omosomes were thus not synchronous with those of B. napus. PMCs with m ore than 6 bivalents and with univalents at the equatorial plate were the most frequent category observed. There were indications that even in these cells, six bivalents often lagged behind at a later stage. Th e apparent separation of parental genomes and subsequent formation of pollen with either of the parental genomes (type II above) explains th e production of plants with 2n = 38 of B. napus morphology among the p rogenies of these hybrids.