Formation of amphidiploids between Brassica napus L. and Raphanus sativus var. Oleifera makino and its stability

The F₁ hybrids obtained by crossing Brassica napus cv. Oro and Raphallus sativus var. oleifera, were cultured in the medium (Ms + 0.2 mg/litre NAA + 3 mg/litre SA + 1 g/litre colchicine + 30 g/litre sugar + 8 g/litre agar) 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. 28 bivalents were formed in the PMC of the amphidiploids. Sometimes 26 bivalents and 1 quadrivalent were found. There are homologous or homoeologous chromosome 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 MI, 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.