Meiotic studies on a Brassica campestris-alboglabra monosomic addition line and derived B. campestris primary trisomics.

Diakinesis chromosomes were studied in pollen mother cells of Brassica campestris (2n = 20, genome AA), B. alboglabra (2n = 18, genome CC), a B. campestris-alboglabra monosomic addition line (AA + 1 chromosome from the C genome), and four derived B. campestris primary trisomics. The nucleolar chromosomes of B. campestris were distinguishable by their morphology at diakinesis. The alien C-genome chromosome in the addition line paired preferentially with the nucleolar chromosome of the A genome. Very rarely, it paired with another pair of the A genome. Thus, it was concluded that the alien C-genome chromosome of the addition line is primarily homoeologous to the nucleolar chromosome and secondarily to another chromosome of the A genome. Three of the four derived B. campestris trisomic plants were identified as B campestris nucleolar trisomics. Trisomy in the fourth plant involved another chromosome. The cytological mechanism underlying the origin of trisomics in the addition line and chromosome homoeology relationships between B. campestris and B. alboglabra are envisaged.