| Altered potency of chromosome 5B in wheat-caudata hybrids
M. D. Upadhya 1) Indian Agricultural Research Institute, New Delhi, India The activity of chromosome 5B to control the intergenomic pairing in hexaploid wheat is suppressed in the presence of the genotype of Ae. speltoides was shown by RILEY et al. (1958; J. Hered. 49: 91-98). Where as, MOCHIZUKI and OKAMOTO (1961; Chromosome Inform. Serv. 2 : 12-14) had shown that the genome of Ae. speltoides also suppresses the activity of this corresponding chromosome at the tetraploid level, in crosses with T. turgidum. It was further indicated by RILEY (Proc. 2nd Intern. Wheat Genet. Symp.), that in 28 chromosome hybrids between T. aestivum and the diploid species Ae. mutica there is considerable meiotic pairing, similar to that observed in 28 chromosome aestivum-speltoides hybrids. However, in 28 chromosome hybrids between T. aestivum and Ae. longissima, RILEY et al. (1959; Nature 183 : 1244-46) had shown that the genotype of longissima does not suppress or modify the activity of chromosome 5B. SARKAR and STEBBINS (1956; Amer. J. Bot. 43 : 297-304) and RILEY et al. (1958; J. Hered. 49 : 91-98) had proposed that Ae. speltoides is the diploid progenator of the B genome of polyploid wheats. Where as, CHENNAVEERAIAH (1660; Acta. Hort. Gotoburgensis 23 : 85-178) had suggested Ae. mutica to be the B genome donor of the polyploid wheats. It is interesting to note that the genomes of both of the diploid species suggested to be the B genome donors share in common the distinctive feature to suppress the activity of chromosome 5B of wheat. According to KIHARA'S genomic grouping Ae. speltoides and Ae. longissima belong to the S group and Ae. mutica belongs to the M group. Therefore, the study was made on the effect of the genotypes of the diploid species belonging to the C group, on the activity of chromosome 5B of wheat. Monosomic plants for chromosome 5B of variety Chinese Spring of T. aestivum were crossed with Ae. caudata as the male parent. The two hybrids raised to maturity showed to be having 28 chromosomes. Analysis for the chromosome associations was made of the first meiotic metaphase from 50 microspores from each plant. Out of 100 cells analysed, 93 cells showed to be having chromosome associations varying from 1II + 26I to 1III + 5II + 15I (Table 1). For only those cells showing the chromosome associations, the mean frequencies of trivalents and bivalents per cell, was 0.15 (range 0-1) and 2.62 (range 1-6) respectively. The range of chromosomes entering associations was found to be from 2 to 13 with a mean of 5.74 chromosomes per cell. Similarly, the mean chiasmata frequency per cell was found to be 2.98. |
| 1) Present address: Department of Horticulture, College of Tropical Agriculture, University of Hawaii, Honolulu, Hawaii, U.S.A. |
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