| In the second back cross generation (BC2), the chromosome number
varied from 27 to 31 (Table 3). Plants with 27
chromosomes occurred with least frequency (1.86 percent),whereas plants
with 14 bivalents occurred in highest frequency (72.81 percent). Frequency
of monosomic plants in the second back cross progenies varied from zero
to 4.55 percent. MOCHIZUKI (1968b) however observed only 0.33 to 7.40 percent
monosomic plants in second back cross generation. The results of the present
study indicate that the occurrence of monosomic plants in tetraploid wheat
is quite low in contrast to that obtained in hexaploids. Therefore, the
maintenance of the monosomic lines of tetraploid wheat requires laborious
work. Moreover, the seeds obtained were also shrivelled. indicating poor
endosperm development occurred in plants which are deficient for a single
chromosome in tetraploid wheat Bijaga Yellow. When monosomic plants were back crossed to Bijaga Yellow, in the BC3 generation, the frequency of transmission of monosomic condition varied from zero to 4.55 percent (Table 4). On an average, the transmission frequency of monosomic condition was 1.68 percent. About 98.32 percent plants obtained in the BC3 generation had 14 bivalents. KIHARA & TSUNEWAKI (1962), TSUNEWAKI (1964a, b) and LACADENA (1973) observed zero percent transmission frequency of mutagenic induced monosomic lines in durum wheat. The low transmission rate of monosomic condition in tetraploid wheats may be due to selection against gametes or zygotes which are definicent in chromosomes. References BOZZINI, A. and GIORGI, B. 1971. Theor. Appl. Genet. 41: 67-74. KIHARA, H. and TSUNEWAKI, K. 1962. Wheat Inf. Serv. 14: 1-3. LACADENA, J.R. 1973. Symp. Genet. Bread. durum wheat, Univ. Bari Italy, 3-37. MOCHIZUKI, A. 1968a. Wheat Inf. Serv. 26: 8-10. MOCHIZUKI, A. 1968b. Proc. 3rd Intern. Wheat Genet. Symp. Aust. Acad. Sci. Canberra. pp. 310-315. Okamoto, 1975. Wheat Inf. Serv. 6: 3-4. Riley, R. 1958. Proc. 10th Int. Congr. Genet. 2: 234-235. Riley, R. 1968. J. Hered. 54: 234-235. Riley, R. and CHAPMAN, V. 1958. Nature. 182: 713-715. SEARS, E.R. 1954. Missouri Agric. Expt. Stn, Res. Bull. 572: 1-59. TSUNEWAKI, K. 1964a. Jap. J. Genet. 38: 270-281. TSUNEWAKI, K. 1964b. Genetica 53: 303-34. |
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