A resynthesized Brassica napus line (AACC, 2n = 38) was successively backcrossed to its parental B. campestris (AA, 2n = 20) to develop monosomic addition lines that contain the different chromosomes of the other parent B. alboglabra (CC, 2 n = 18). Special emphasis was put on identifying monosomic addition lines with B. alboglabra chromosome(s) carrying genes for black seed colour. Four different types of monosomic addition plants were obtained. One of them harboured a B. alboglabra chromosome with gene(s) for black seed colour while another type of monosomic addition plant had the B. alboglabra chromosome with the gene for white flower colour.The remaining two carried hitherto unmarked C-genome chromosomes and were distinguished from each other by the morphology of the alien chromosome at diakinesis of meiosis. Meiotic studies revealed that the monosomic addition plants for the white flower colour or black seed colour had a higher trivalent frequency in the pollen mother cells when compared with the two unmarked monosomic addition plants. Two different types of double-monosomic addition plants were also obtained. Such double-monosomic addition plants will be useful to reveal intragenomic homoeology of the B. alboglabra chromosomes.

The fatty acid composition of the oil of four resynthesized rapeseed (Brassica napus L.) lines resulting from crosses between B. campestris L. and B. alboglabra Bailey was compared with that of the mid-parent value. Low palmitic acid content was partially epistatic over high. High oleic acid content could be either partially hypostatic to or transgressively epistatic over low content of this fatty acid, depending on the erucic acid contents of the parental species. Epistasis was observed for low linoleic acid content in two crosses whereas additive gene action was shown for this fatty acid in the other two crosses. Partial or transgressive epistasis was observed for low linolenic acid content. High eicosenoic acid content was generally epistatic over low. Partial epistasis was observed for high erucic acid content in three crosses but hypostasis was also observed in one cross. Oleic acid content played a key role in the change of fatty acid composition. Regarding the inheritance of erucic acid content, the hypothesis was substantiated that B. napus contained two genes for this fatty acid residing in the genomes from B. campestris and B. oleracea. Caution should be taken in accepting the proposed hypothesis (Krzymanski and Downey, 1969) that there is a series of erucic alleles based on the phenotypic value of erucic acid content, because the influence of different genetic backgrounds and/or ploidy level on the allelic performance is not taken into consideration.