| Frequency of aneuploids in euploid progenies of hexaploid
Triticale H.M.I. HAFIZ and A.S. LARIK* Botany Department, New Campus, Punjab University, Lahore, Pakistan Synthetic hexaploid triticales are cytologically unstable, and segregate a certain frequency of aneuploids in the progeny of 42-chromosome euploids (TSUCHIYA & LARTER 1971). These anuploids, particularly hypoploids including monosomics and nullisomics, have been demonstrated to give lower seed set in the primary floret, fewer seeds per spikelet, per spike and per plant than those in the euploid with 42-chromosome (TSUCHIYA 1973). Moreover, these aneuploids segregate a high frequency of aneuploids in their progenies as reported by TSUCHIYA (1973) and TSUCHIYA & LARTER (1969). The results obtained from the extensive study of meiotic chromosome variation in 300 plants from three cultivars (NIAB-T-77, NIAB-T-158-4 and NIAB-T-103) clearly indicate that the hexaploid triticales are cytologically unstable. Overall average frequency of euploids (2n=42) ranged from 14% to 22% for three cultivars (Table 1). The frequency of monosomics and nullisomics ranged from 45% to 48% and 30% to 40% in the progeny of hexaploid triticales respectively. Data in Table 1, obviously reveal that: 1) Hexaploid triticales are cytologically unstable. They segregate various frequencies of aneuploids in euploid plants. 2) The cytological stability represented by the frequency of euploids in the population is controlled at least to some extent, by a genetic factor(s). Similar results were also recorded by MERKER (1973) and TSUCHIYA (1969, 1974). MERKER (1973) and TSUCHIYA (1974) have reported higher frequencies of hypoploids and lower frequencies of euploids in advanced strains of hexaploid triticales. Telocentric chromosomes were not observed in the present material (NAKAJIMA 1953, 1965) and KROLOW (1966), while MERKER (1973) and TSUCHIYA (1969) reproted the occurrence of telocentric chromosomes. These differences may be attributed to the differences of the materials studied and the environmental effect on cytological behaviour in meiotic division. However, cytological techniques employed could also be one of the causes of the differences. |
| * Department of Plant Breeding and Genetics, Sind Agriculture University, Tandojam, Pakistan. |
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