Abstract
Embryological studies were made to clarify the developmental processes leading to seed collapse following crosses between diploid Brassica chinensis (2x=20) and autotetraploid Brassica pekinensis (4x=40).
It was observed that the hybrid embryos from the reciprocal crosses appeared to develop normally in the early developmental stage, but they generally failed to develop beyond the globular stage as the degeneration of endosperm progressed. Exceptionally, a few triploid plants were obtained from the 4x (_??_)×2x (_??_) cross.
In 2x×4x crosses, cell wall formation in the endosperm was completely inhibited, and there occurred abnormal vacuolization in endosperm which was accompanied with various nuclear irregularities, resulting in a complete degeneration of whole endosperm, including embryo, in all ovules.
In 4x×2x crosses, the amount of endosperm was smaller but cell wall formation took place earlier than in the parents. However, the endosperm, including embryo, was disintegrated around 15 days after pollination.
The possible cause of seed failure was discussed considering various abnormalities observed during the developmental stages.
