| Discussion The frequency of chromosomal abberations induced in dormant seeds after X-ray doses indicates that wheat was less affected than rye. Since, the plants having small sized chromosomes are usually more radioresistant than plants with large chromosomes, the low chromosomal radiosensitivity of 6x wheat is not surprising (BHASKARAN & SWAMINATHAN 1960). However, in our material of triticale, meiosis was irregular in the treated material as well as in the control. The main meiotic irregularities were univalents, laggards and micronuclei in the tetrads. In addition to that spindle formation was much disturbed which consequently gave rise to polyads. Perhaps the main cause of meiotic disturbance is the incompatability between rye and wheat genomes located in one cell, and the inactivation of some loci of the rye chromosomes in some cells, as suggested by RILEY (1960). From these studies of wheat lines with added rye chromosomes, it is concluded that rye chromosomes are unable to function adequately in the presence of full set of wheat chromosomes. Observations reported by SHKUTINA & KHVOSTOVA in 1971 are fully accorded with RILEY'S opinion in showing that rye chromosomes are not controlled by wheat chromosomes in the process of cell division. Their studies indicated that chromosomes of the rye genome in triticale not only lag behind the wheat chromosomes, but also keep apart from them in the course of meiosis. This could sometimes be observed in prophase as well as in metaphase and anaphase. Presumably, the separation of rye chromosomes is not controlled by spindle fibres and as such these are distributed randomly throughout the cell. This is in accordance with the abservations made by SANCHEZ-MONGE (1958), VETTEL (1960) and VEIMARCK (1975). Inspite of the fact that meiosis was disturbed in the control of triticale, however the present results show an increase of irregularities with the increase in the mutagenic dose. Perhaps the genetic difference between rye and wheat chromosomes could be the possible reason for higher radiosensitivity in triticale than in wheat. Literature cited BHASKARAN, S. and M.S. SWAMINATHAN. 1960 Polyploidy and radiosensitivity in wheat and barley. 1. Cytological and cytochemical studies (Part 1.) Genetics 31: 449-480. DARLINGTON, C.D. and L.F. LACOUR 1976. The handling of Chromosome (Sixth edition): 36-39. LARIK, A.S. 1978. Morphology and cytology of different aneuploids in Avena sativa L. Cytologia 43: 695-704. LARIK, A.S., and H. THOMAS, 1979. Inheritance of chromosome deficiency and duplication in Avena sativa L. Cytologia 44: 835-848. RILEY, R, 1960. The meiotic behaviour, fertility and stability in wheat-rye chromosome addition lines. Heredity 14(1): 89-100. SANCHEZ-MONGE, E. 1958. Hexaploid Triticale. Proc. 1st Int. Wheat Genet. Symp. 1958: 181-194 SHKUTINA, F.M. and V.V. KHVOSTOVA, 1974. Cytological Investigation of Triticale. Theor. Ap Genet. 41: 109-119. VETTEL, F. 1960 Mutation experiments on wheat-rye hybrids (Triticale) 11. Cytological and fertility experiment on triticale. Rempan and its mutant. Zucrter 30: 181-189. WEIMARCK, A. 1975. Cytogenetic behaviour in octoploid Triticale. Hereditas 80: 121-130. |
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