Abstract
1. An F1 plant was obtained from the cross of an induced autotetraploid Aegilops squarrosa with a diploid Secale cereale. And two BCF1 plants were obtained from the back cross of the F1 plant with S. cereale (Table 1, Fig. 1).
2. In the cross 4x-Ae. squarrosa×S. cereale the F1 plant was observed to have 2n=21 chromosomes in PMC's. It indicated that this plant was a triploid hybrid carrying DDR genomes. The chromosome pairing at the first metaphase in the meiosis in this F1 plant showed 7II+7I in most PMC's, while some of the cells showed 6II+9I or 8II+5I (Tables 2 and 3, Figs. 2-5). Out of eight bivalents seven might be formed by the autosyndesis between the chromosomes in D genome, and the remaining one might be an intra-genome pairing of the chromosomes in R genome. Such an intra-genome pairing was found in PMC's of 2.8%.
3. It was observed that the number of the somatic chromosome in the BCF1 plants which were obtained from the back cross were 21 in one plant and 23 in other (Figs. 7-8). It seems from their karyotype analysis that the genome constitution of the BCF1-1 plant might be a haploid set of Ae. squarrosa and a diploid set of S. cereale, that is, D and RR genomes. And the BCF1-2 plant might be a hyper-triploid plant carrying DRR genomes and two extra-chromosomes. One of these two chromosomes seems to belong to the D genome and the other to the R genome.
4. As shown in Table 4, the chromosome pairing showed 7II+7I in most cells in the BCF1-1 but 5II+11I or 6II+9I in some cells (Fig. 9). Further, the cells having 8II+5I were rare (0.8% of total, Fig. 10). This fact suggests that an intra-genome pairing may take place between the chromosomes in D genome.
5. Chromosome pairing at the first metaphase in the BCF1-2 plant is given in Table 6. In most of PMC's, the chromosome configuration was 7II+9I or 6II+11I. 9.6% of the cells had either 1 or 2 trivalents together with the bivalents (Figs. 12-14). The chromosomes of S. cereale may be larger than those of Ae. squarrosa. Therefore the chromosome associations observed could make clear what genomes they belonged to (Table 6). In this plant as well as the BCF1-1 plant, it was confirmed from this situation that an intra-genome pairing may take place between the chromosomes in D genome.
6. In every plants, at the first metaphase in the meiosis, it was observed occasionally that two univalents were laid in tandem each other and sometimes appeared to be connected by a single chromatin thread (Figs. 5-6). These are called univalent associations. It was considered that these univalent associations were due to the heterochromatin fusion.
