Variation in the Number of Bivaleut Chromosomes in the F1 Hybrids between Triticum durum and Aegilops ventricosa
1931 Volume 45 Issue 537 Pages 424-445
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1931 Volume 45 Issue 537 Pages 424-445
In the present paper the writer has made statistical studies on the variation of the number of bivalent chromosome in the first meiotic metaphase of the sterile F1 hybrids (Pls. IV) between Triticum durum, DESF. var. Reichenbachii, KÖRN. and Aegilops ventricosa, TAUSCH. under various conditions.
The results of observations are summed up as follows:
1. The diploid number of chromosomes is calculated as 28 in the P.M.C. as well as in the E.M.C., corresponding to the sum of the haploid numbers of the parents. In my observations the number of bivalents varied from 0 to 4 in the P.M.C. (Figs. 1-5) and 0 to 3 in the E.M.C. (Figs. 6-9). The modal value of the number of bivalents is always 0. Usually, two homologous chromosomes conjugate loosely at one end, but a compact bivalent (Fig. 10) is observed one time. Twice found trivalent chromosomes (Fig. 11) are treated here as bivalents
2. It may be probable that the conjugation of chromosomes is derived mostly from autosyndesis between the genoms A and B, these having been originated from the Triticum-parent, and rarely from allosyndesis between Triticum and Aegilops-chromosomes (cf. Tabs. 13 and 14).
3. The number of bivalent chromosomes in P.M.C. -s from the same plant shows a considerable variation in materials fixed at different dates (Tab. 1).
4. The writer is not able, as far as his observation goes, to find any difference in the variation of the chromosome conjugation among individuals (Tab. 2), it is also independent of the direction of crosses (Tab. 2), position of spikelets (Tab. 3) and florets (Tab. 4), if they are only fixed at the same date.
5. Generally, it may be said that the variation in the number of bivalent chromosomes in P.M.C. and E.M.C. of the selfsame floret is similar (Tab. 5).
6. The diurnal (Tab. 6) and seasonal (Tab. 7) differences in the number of bivalent chromosomes may depend mostly upon the temperature and the duration of exposure to temperature.
7. The writer could not find a remarkable difference in chromosome conjugation between the plants in the field and those of pot-cultures (Tab. 8), neither in regard to the moisture of the soil (treated for 46 hours, Tab. 9) nor to the duration of exposure to light (treated for 46 hours, Tab. 10). In these cases, however, the number of bivalents is generally lower than in the controls.
8. One plant was preserved for 3 hours in the green house at the temperature about 30°C, and then it was brought to the ice-chamber at about 8°C, and kept for 3 hours. While the other plant, on the contrary, was brought from the ice-chamber to the green house. Comparing these two plants, it was impossible to find a difference in the number of bivalent chromosome. (Tab. 11).
9. The number of bivalents was counted in materials kept in chambers at different temperatures (ca. 6, 15, 24 and 38°C) for 12 hours. At lower temperatures (6 and 15°C) the division of the P.M.C. was almost normal, but sometimes several chromosomes were brought together in a mass (Fig. 12); at the highest temperature (38°C) used, however, the division was extremely disturbed (Fig. 13), bivalent chromosomes could not be observed. The higher the temperature rose up, the fewer became the bivalent chromosomes, and their numher varied considerably in the range of 15-24°C, as can be seen in Fig. 14. The difference between the means of bivalent numbers at the two extremes varies from 0.20 to 0.43 (mdif =±0.072), and perhaps can be taken statistically as significant (Tab. 12).
10. Although the variation in the number of bivalent chromosomes was perhaps influenced also by other conditions, as far as the writer's observation goes, it was chiefly caused by the temperature (Tab. 15).
