The influence of the B genome on chromosome pairing in trigeneric Aegilops X X Triticum X Secale hybrids

A cytological study of the trigeneric (Aegilops X Triticum X Secale) hybrids, with and without the B genome, was made. The species studied were Triticum aegilopoides, Triticum monococcum, Triticum durum, Triticum dicoccum, Aegilops squarrosa, Aegilops ventricosa, Secale cereale and Secale montanum. The chromosomes of Secale do not pair with the chromosomes of Triticum or Aegilops, irrespective of the presence or absence of the B genome. No inhibitory effects of Secale were observed in the trigeneric hybrid which involved only the diploid species of three genera viz. Triticum aegilopoides, Aegilops squarrosa and Secale cereale. A study of the trigeneric hybrids, in which polyploid species of Triticum and Aegilops were used, indicated that in the hybrids with the genomic constitution ADMvR about 5 bivalents were formed. In the hybrids (ABDMvR), the average number of bivalent was as low as 1, but multivalent formation was not influenced by the presence of the B genome. The studies confirm the cytological similarities between the natural and synthetic amphiploids with the genomes AABBDD. The genetic diploidizing system operating in polyploid Aegilops seems to be different from that operating in the polyploid species of Triticum. The tetraploid Aegilops ventricosa appears to possess a gene(s) which affects homoeologous pairing and alters the potency of the B genome in the trigeneric hybrids. The genetic control of the meiotic process is very complex and does not seem to rest entirely in the B genome but is significantly influenced by factors in all other participating genomes.