Nucleolar competition in different (A/b)(a/b)rr and ddrr tetraploid triticales

Nucleolar activity was analysed in hybrids between Aegilops squarrosa and Secale cereale or Secale silvestre and in different tetraploid triticales with A/B mixed genomes, using phase contrast, C-banding and Ag-NOR staining techniques. The results revealed that nucleolar activity of the satellite chromosome pair 1R of S. cereale as well as that of S. silvestre was suppressed by the presence of the nucleolus organising chromosome of Aegilops squarrosa. In all combinations of tetraploid triticales with A/B mixed genomes containing satellite chromosome pairs IB and 6B or only chromosome pair IB, nucleolar activity was restricted to satellite chromosomes from the B genome while those belonging to the R genome of rye and A genome of wheat were completely suppressed. Satellite chromosome pair 1R of rye was active in producing nucleoli, only in combinations missing IB and 6B while nucleolar organizer regions from A genome remained inactive.