Digenomic triploids for an assessment of chromosome relationships in the cultivated diploid Brassica species

Abstract

To assess the chromosomal relationships in the cultivated diploid Brassica species, four digenomic triploid combinations were synthesized and meiotically analyzed. Two of the four digenomic combinations contained the B genome of B. nigra, one with two (BC.B) and the other with only one B genome (C.BC). In these combinations preferential pairing between the two homologous genomes with the third single genome was predominant. Since gene actions suppressing pairing between chromosomes of related genomes had not been proven to exist in Brassica, this phenomenon is assumed to be conditioned by structural chromosomal differences reflecting the distant phylogenetic relationship of B. nigra to each of B. oleracea (CC) and B. campestris (AA). On the other hand, two other digenomic triploids having two A genomes and one C genome showed a low preferential pairing of the two homologous A genomes (to form 10II + 9I). Moreover, a high tendency for an allosyndetic pairing between the A and C genomes was expressed by the formation of one or more trivalents in over 50% of PMCs in the two combinations A.AC and AC.A. This demonstrated a high meiotic pairing potential and a small evolutionary difference between the chromosomes of B. campestris (AA) and B. oleracea (CC).