| Genome analysis of Aegilops mutica Boiss. based
on the chromosome pairing in the hybrids with or without B-chromosomes
SHOJI OHTA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Mozume, Muko, Kyoto 617, Japan Aegilops bicornis, Ae. longissima, Ae. sharonensis, Ae. speltoides, Ae. caudata, Ae. comosa, Ae. uniaristata, Ae. umbellulata and Triticum boeoticum were crossed by Ae. mutica with or without B-chromosomes(Bs), and A-chromosome pairing at MI of PMCs in the F1 hybrid plants was observed to estimate the genome homology between Ae. mutica and these nine species. The mean chiasma frequencies per cell and their ranges in these F1 hybrids are shown in Fig.1. The F1 hybrids without B-chromosomes(OB) from the crosses of Ae. bicornis, Ae.longissima, Ae. sharonensis, Ae. speltoides, Ae. comosa and T. boeoticum to Ae. mutica showed a very high frequency of A-chromosome pairing with a high chiasma frequency, while those from the crosses of Ae. uniaristata, Ae. caudata and Ae. umbellulata to Ae. mutica showed a lower frequency of A-chromosome pairing and/or a complicated configuration of A-chromosome pairing with a high frequency of multivalents. On the contrary, the F1 hybrids with 2Bs from most cross combinations showed a very low frequency of A-chromosome pairing characteristically with no chiasma in their PMCs. In contrast, a high frequency of bivalents was found in the 2B hybrids from the cross of Ae. speltoides x Ae. mutica. In addition to these results from chromosome pairing in F1 hybrids, partially fertile 0B hybrid plants were obtained from the crosses of some strains of Ae. speltoides to Ae. mutica and their pollen fertility was up to 16.7%. From one of these fertile hybrids, six plump caryopses were obtained by open pollination. Three of them normally germinated, and two of the obtained seedlings had 14 chromosomes and the other had 15 chromosomes in their root tips. Therefore, the normal pollen grains in the partially fertile F1 hybrids are reasonably assumed not to be unreduced gametes but to be normal gametes with seven chromosomes. It is well-known that B-chromosomes of Ae. mutica remarkably suppress the pairing between homoeologous or partially homologous chromosomes but do not affect the pairing between fully homologous ones. Considering the present data and this fact, I conclude that the genome of Ae. mutica is most closely related to that of Ae. speltoides. |