| On the basis of these data the following inferences can be drawn. 1. That chromosome 5A of T. monococcum present in T. zhuhovshyi is not identical to the 5A of Chinese Spring (T.aestivum) or 5A of T. timopheevi, with respect to the genes controlling chromosome pairing. 2. That UPADHYA and SWAMINATHAN (1967) observed that the absence of chromosome 3D in the 27-chromosome hybrid between Chinese mono-3D and rye showed significant increase in the homoeologous pairing among wheat chromosomes. This has been shown by MELLO-SAMPAYO (1968) to be due to the presence of an inhibitor of homoeologous chromosome pairing on chromosome 3D of Chinese Spring. With respect to 3D, the chromosome complement of the 41-chromosome hybrid between mono-5B and timopheevi-squarrosa amphidiploid is: 1 of 3D Chinese + 1 of 3D squarrosa, whereas in the case of 41- chromosome hybrid of mono-5B x zhukovskyi, there is only one dose of 3D of Chinese. It, therefore, appears that one extra dose of 3D from squarrosa in the first case was able to complement further the action of 5B from timopheevi. 3. That the potency of chromosome 5B of T. timopheevi appears to be of much lower order than the potency of 5B of T. aestivum, and that 5B of timopheevi does not therefore, compensate fully for 5B of Chinese Spring. 4. That chromosomes 3D and 5D present in the hexaploid wheats and carrying genes controlling homoeologous chromosome pairing were originally carried by the donor of the D genome, Ae. squarrosa and that present day squarrosa also carries them. 5. That the corresponding chromosome 5A of T. monococcum in T. zhukovskyi does not carry the gene system identical to that located on 5A of T. aestivum; as such the 5A system of aestivum very likely appeared after the incorporation of the A genome in tetraploid wheats. Literature Cited FELDMAN, M. 1966a. The mechanism regulating pairing in Triticum timopheevi. W.I.S. 21: 1-2. FELDMAN, M. 1966b. The effects of chromosomes 5B, 5D and 5A on chromosomal pairing in Triticum aestivum. Proc. Natl. Acad. Sci. 55: 1447-1453. MELLO-SAMPAYO, T. 1968. Homoeologous pairing in pentaploid hybrids of wheat. Proc. 3rd Intl. Wheat Genet. Symp., Aust. Acad. Sci., Canberra, pp. 179-184. UPADHYA, M. D. and M. S. SWAMINATHAN 1963. Chromosome pairing and morphological characters in 27- and 28-chromosome hybrids between rye and monosomics of homoeologous group V of bread wheat. Indian J. Genet. 23: 225-231. UPADHYA, M. D. and M. S. SWAMINATHAN 1965. Studies on the origin of Triticum zhukovskyi and on the mechanism regulating chromosome pairing in Triticum. Indian J. Genet. 25: 1-13. UPADHYA, M. D.and M. S. SWAMINATHAN 1967. Mechanism regulating chromosome pairing in Triticum. Biol. Zentral. Suppl. 86: 239-255. (Received September 8, 1970) |
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