EMBRYOLOGICAL STUDIES ON CROSS-INCOMPATIBILITY BETWEEN 2x AND 4x IN BRASSICA

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Abstract
Studies were made to clarify the developmental process leading to seed collapse following cross between diploid Brassica chinensis (2x = 20) and autotetraploid B. pekinensis (4x = 40). 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, although a few triploid plants were obtained from the 4x ([female]) X 2x ([male]) cross, In 2x X 4x crosses, cell wall formation in the endosperm was completely inhibited, and there occurred abnormal vacuo-lization in endosperm which was accompanied with various nuclear irregularities, resulting in a complete degeneration of whole endosperm, including embryo, in all ovules. In 4x X 2x crosses, the amount of endosperm was smaller but cell wall formation took place earlier than in the parents. The endosperm, including embryo, was disintegrated around 15 days after pollination.