Sterility and apomictic embryo-sac formation in Raphanobrassica

Abstract

The amphidiploid hybrid Raphanobrassica was easily produced from crosses between autotetraploids of the parent species. On an average 0.2 hybrid seeds were obtained per pollinated flower. Seed setting was extremely bad in the first generation hybrids, only 0.1 seeds per pollinated flower. Repeated selections during 6 generations have improved seed fertility. Seed setting has been raised to 2.3 seeds per pollinated flower, which is equivalent to a seed fertility of 13%. The prospects for Raphanobrassica as a new forage crop seem to be good. An economic seed production has, however, first of all to be achieved. The fertility needed for such a production is discussed and estimated to be around 40%. It is concluded that the main cause of the sterility is a disturbance of a more general nature in the interplay between the two parent genomes. As a result of this, the present material exhibits a high frequency of unfertilized and/or degenerated embryo-sacs. Aposporic embryo-sacs in varying frequencies are also found in most plants. The causes of the formation of aposporic embryo-sacs in this species and the possibilities for the production of a facultatively apomictic Raphanobrassica are briefly discussed.