MEIOTIC STUDIES ON A BRASSICA-CAMPESTRIS-ALBOGLABRA MONOSOMIC ADDITION LINE AND DERIVED BRASSICA-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 the ir morphology at diakinesis. The alien C-genome chromosome in the addi tion line paired preferentially with the nucleolar chromosome of the A genome. Very rarely, it paired with another pair of the A genome. Thu s, it was concluded that the alien C-genome chromosome of the addition line is primarily homoeologous to the nucleolar chromosome and second arily to another chromosome of the A genome. Three of the four derived B. campestris trisomic plants were identified as B campestris nucleol ar trisomics. Trisomy in the fourth plant involved another chromosome. The cytological mechanism underlying the origin of trisomics in the a ddition line and chromosome homoeology relationships between B. campes tris and B. alboglabra are envisaged.