The Response of Haploid Secondary Embryoids and Secondary Embryogenic Tissues of Winter Oilseed Rape to Treatment With Colchicine

SUMMARY It was shown by experiment that the treatment of cultured haploid detached secondary embryoids and secondary embryogenic tissues of Brassica napus ssp. oleifera with colchicine resulted in diploidy, tetraploidy and mixaploidy. The proportions of the different ploidy levels so induced depended on the concentration of colchicine used and the duration of treatment. The highest levels of diploidization were obtained by exposing the tissues to 0.05 % colchicine in 2% dimethylsulphoxide for 72 h. The capacity for secondary embryogenesis was retained in colchicine‐induced diploid, tetraploid and mixaploid tissues, and the majority of the resulting second generation secondary embryoids were of the same ploidy as the parental material. This indicates the stability of the secondary embryogenic potential irrespective of changes in ploidy level. It is suggested that the ability to produce secondary embryoids is a consequence of haploidy and homozygosity. That the phenomenon is not a consequence of growth in culture is indicated by the fact that secondary embryoids are also produced occasionally on mature glasshouse‐grown plants regenerated from secondary embryoids. It is concluded that a system is now available for the continuous production of large numbers of haploid and homozygous diploid plants, and plants of other ploidy types, all derived from the same haploid anther embryoid. Such a system will be of value for oilseed rape breeding and for genetical and biochemical studies of somatic embryogenesis.