Optimum age of siliques for rescue of hybrid embryos from crosses between Brassica oleracea, B. rapa and B. carinata
Interspecific hybrids were produced from crosses involving Brassica rapa var. Yellow Sarson (AA), Canadian B. rapa (AA) cultivars, B. oleracea var. alboglabra (CC), B. oleracea var. italica (CC), rapidcycling B. oleracea (CC) and B. carinata (BBCC) to introgress the yellow seed color or self-incompatibility genes into B. napus. Embryo rescue technique was employed for this purpose. In interspecific crosses where a CC genome species was used as the female parent, a significantly lower number of ovules were fertilized compared to the crosses where the BBCC genome species was female. Embryo growth and development were slower in the crosses where the CC genome species was female than in the crosses where BBCC genome species was female. The efficiency of the embryo rescue technique from 16 to 40 d after pollination (DAP) with 4-d intervals was investigated in the crosses using CC genome species as female. The highest numbers of embryos were rescued between 20 and 28 DAP depending upon the specific cross undertaken. However, the survival rate of the embryos rescued at 20 DAP was very low compared to the embryos rescued at 24 and 28 DAP. The survival rate of the embryos rescued at 32 DAP was generally high, but the number of embryos rescued at this stage was significantly lower than at 24 and 28 DAP. No embryos were obtained at 16 DAP or at 40 DAP. Thus, using the CC genome species as female parent, the maximum efficiency of the embryo rescue technique was achieved when embryos were rescued between 24 and 28 DAP. In the case of crosses using the BBCC genome species as female, rescue of hybrid embryos was successful at 18 and 22 DAP. Key words: Brassica, interspecific cross, embryo rescue, embryo development