The integenomic pairing of chromosomes of Ae. crassa, detected by the trivalents in the hybrids with wheat, should be expressed as bivalents in the haploid Ae. crassa and might be the cause of the quadrivalents observed at meiosis in Ae. crassa.

The action of chromosome 5B could be expected to limit the chromosome pairing to homologues in the wheat hybrids. However, in T. aestivum x Ae. squarrosa (RILEY and CHAPMAN 1960) the action of chromosome 5B did not prevent the pairing of chromosomes of Ae. squarrosa and wheat D genome chromosomes. The D genome of T. aestivum must, therefore, still be very similar to the D genome of Ae. squarrosa. The lack of pairing in Ae. vavilovii x T. aestivum demonstrates that the D genome of Ae. vavilovii is greatly modified from the D genome of wheat and, therefore, from that of Ae. squarrosa. In Ae. crassa x T. aestivum there was the equivalent of one paired genome. Our investigations did not produce evidence to show whether the pairing involved chromosomes of either the D, the D² or both of these genomes of Ae. crassa with the D genome of wheat. It is believed that Ae. crassa and Ae. vavilovii have in common the genomes D and M^cr which they obtained during their evolution from the tetraploid Ae. crassa (M^crD). If this is correct then this D genome did not pair in Ae. vavilovii x T. aestivum and may not therefore have paired in Ae. crassa x T. aestivum. We have been unable to obtain the hybrid Ae. crassa 4x x T. aestivum which would compare this D genome with the D genome of wheat.

The chromosome pairing in haploid Ae. crassa and Ae. crassa x S. cereale (Table 1) was little more than could be expected from the intergenomic pairing of the chromosomes of Ae. crassa which was seen in the wheat hybrids. The absence of further homoeologous pairing, particularly in the haploid, leads us to speculate that a form of genetic control must operate to prevent such pairing.

Literature Cited

CHAPMAN, V. and T.E. MILLER. 1977. Haploidy in the genus Aegilops. Wheat Inf. Serv. 44: 21-22.

CHENNAVEERAIAH, M.S. 1960. Karyomorphologic and cytotaxonomic studies in Aegilops. Acta Horti-Gotoburgensis 23: 85-178

KIHARA, H. 1957. Completion of Genome-analysis of three 6x species of Aegilops. Seiken Ziho 8: 3

KIHARA, H. and M. TANAKA. 1970. Addendum to the classification of the genus Aegilops by means of genome analysis. Wheat Inf. Serv. 30: 1

RILEY, R. and V. CHAPMAN. 1960. The D genome of hexaploid wheat. Wheat Inf. Serv. 11: 18-19

SIDDIQUI, A.K. and J.K. JONES. 1967. The D genomes of Aegilops crassa Boiss. Bol. Genet. Inst. Fitotec Castelar 4: 29-31

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