Formation of amphidiploids between Brassica napus L. and Raphanus sativus var. oleifera Makino and its stability.

摘要

The F1 hybrid embryos, obtained by crossing Brassica napus cv. Oro and Raphanus sativus var. oleifera, were cultured in MS medium + 0.2 mg NAA + 3 mg BA + 1 g colchicine + 30 g sucrose + 8 g agar/litre for 5 days. Many buds obtained carried 56 chromosomes. With the above technique, it is possible to obtain stable amphidiploids by the routine hybridization between Brassica and related species. Some 28 bivalents were formed in the PMC of the amphidiploids. Sometimes 26 bivalents and 1 quadrivalent were found. There are homologous or homoeologous chromosomes in one genome or between two genomes of the amphidiploids. Another type of meiosis was discovered in the amphidiploids in which 56 chromosomes did not form bivalents and the chromatids could be detected in metaphase I, several chromosome masses formed at anaphase and the pollen was sterile. This is the first cytological evidence of sterility in the amphidiploids of rapeseed. Unbalanced division was observed in the R. sativus var. oleifera at anaphase I of meiosis which formed two types of pollen, one with 8 chromosomes, and another with 10 chromosomes. This could be the starting point where two basic chromosome numbers contributed to the genome evolution.