Cytology of the addition lines :

The monosomic addition lines have 29 chromosomes, i.e., 28 wheat chromosomes and one from Agropyron. If the Agropyron chromosome had homologous segments with wheat chromosomes the monosomic addition line should have a trivalent and 13 bivalents, while no chromosome pairing between wheat and Agropyron chromosomes would be found and the Agropyron chromosome would remain as a univalent if it had no homology with any of the wheat chromosomes. As indicated in Table 2, six of the seven Agropyron chromosomes have homologous segments in durum wheat chromosomes. Wheat - Agropyron chromosome pairing in e₂, e₃ and e₅ monosomics was more frequent than in e₁, e₆ and e₇ lines, while no pairing was found in the e₄ line.

Such chromosome pairing may indicate the relationships between wheat and Agropyron chromosomes, namely the E genome of Agropyron elongatum (2n=14) may be semi - homologous to one of the genomes of durum wheat. Thus in the monosomics with added single alien chromosomes, the homology of the alien chromosome to host chromosomes can be analyzed more precisely than in the F₁ or pentaploid hybrids.

In general, the univalent chromosome divides at first anaphase of meiotic division. At the second anaphase and telophase the morphology of the univalent alien chromosome can be identified clearly and the morphology two different alien chromosomes can be compared at the same time in double monosomic addition lines. The morphological analysis of seven Agropyron chromosomes has been nearly completed.

Pentavalent chromosome association shown in the e₅ monosomic addition line suggests that both arms of e₅ chromosome are partially homologous to two different wheat chromosomes.

The disomic addition lines should have 15 pairs in their PMC's, however, 5-30 per cent of PMC's had univalents. The frequencies of such PMC's differ in different addition lines. Presumably the irregularity resulted from asynapsis of the alien pair, due to the unbalance between the alien chromosomes and the complement of the host. As a result, reduced fertility and instability of alien chromosomes were found in the addition lines.

As indicated in the Table 3, e₁e₁, e₂e₂ and e₄e₄ lines are fairly stable, producing only a small portion of progeny with deviating chromosome numbers, but in e₃e₃ e₅e₅ and e₇e₇ lines, 23 to 48 per cent of the progeny had deviating chromosome numbers.

In the double monosomic addition plants obtained from the cross between disomic addition lines, a decrease in chromosome pairing between the host and alien chromosomes was observed. This may be due to an interference effect of the two alien chromosomes on host-alien chromosome pairing.

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