COMPARATIVE EFFECTS OF VARYING DOSES OF X-RAYS AND FAST NEUTRONS OF THE GROWTH AND DEVELOPMENT AND INDUCTION OF CYTOLOGICAL CHANGES IN TETRAPOLID AND HEXAPLOID WHEAT
Experiments have shown that while the tetraploid wheat, Jaya 808 (4n = 28), requires about 25,000 r of 220 kvp x rays for reducing fertility of spikelets to 50%, the hexaploid variety Kemphad (6n = 42) requires about 40,000 r without causing appreciable reduction in the vigor of growth and serious developmental irregularities. Meiotic studies on the X/sub 1/ plants have revealed that one of the striking irregularities is the quite high frequency of unoriented univalent chromosomes at metaphase and anaphase of the first meiotic division. For instance, in Kemphad the frequency of such univalents is 306.71 per 100 pollen mother cells against 37.75 in the control; in Jaya it is 25.90 against nil in the control. It has been observed that as far as the chromosomal aberrations are concerned the hexaploid is less radioresistant than the tetraploid. The evidence on the effect on the growth and developmeni processes suggests that at certain dosage levels factors other than chromosomal damage may become more harmful. Experiments on the relative biological efficiencies of 220 kvp x rays and fast neutrons on the induction of various types of aberration in the resting stage chromosomes of dry wheat grains were carried out to ascertain the appropriate fast neutron doses for future experiments. The flux of fast neutrons was 10/sup 10/ sec/cm/sup 2/. The seeds were exposed for 2, 4, 8 and 18 minutes. The RBE value has been found to vary at different dosage levels and with different types of aberration. It has, however, been determined that the most appropriate RBE value of fast neutrons for inducing di-, tri- and multicentric chromosomes would be about 9. It has further been observed that high doses of fast neutrons induce a large number of chromatid aberrations in the dry seeds. This finding is unexpected, and calls for reconsidering the hypotheses on the mechanism of induction of chromosomal aberrations by ionizing radiations. (auth)
- Research Organization:
- Atomic Energy Establishment, Trombay, India
- NSA Number:
- NSA-13-006237
- OSTI ID:
- 4288356
- Report Number(s):
- A/CONF.15/P/1641
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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