| Recombination between the chromosomes of wheat and
rye - A possibility D. SINGH and B. C. JOSHI Division of Genetics, Indian Agricultural Research Institute, New Delhi-12, India In an attempt to transfer desirable characters from Secale cereale (2n=14) to Triticum aestivum (2n=42), F1 hybrids were produced between them. We have isolated presumably a spontaneous mutation at the 5B locus of T. aestivum, in one of the 28 chromosome F1 hybrids leading to pairing of the presumably homoeologous chromosomes of wheat and rye, with the result that several bivalents, trivalents and occasional quadrivalent were formed (as given in Table 1). The normal control cross showed very little pairing among its 28 chromosomes. In the 5B mutated hybrid there were several cells in which there were 11 bivalents, out of which many were close-ring type with distinct interstitial chiasmata and several cells showed quadrivalents. Since BIELIG and DRISCOLL (1970) have provided evidence that in the absence of long arm of chromosome 5B the wheat and a rye telocentric chromosomes pair, we postulate that in the F1 hybrid reported here there is pairing between wheat and rye chromosomes. NAKAJIMA (1952) also reported the cytological analysis of an F1 hybrid between wheat and rye which was also a mutation at a locus suppressing pairing of homoeologous chromosomes in which as many as from 5 to 11 bivalents and trivalents and quadrivalents per cell were formed. Since at the time the 5B system was not discovered and there was no evidence to suggest that the wheat and rye chromosomes can pair, it was postulated by NAKAJIMA that there would not be any syndesis between the genomes of wheat and rye. The extremely low frequency (3.5 percent) of pairing between wheat and rye chromosomes, in the absence of 5BL of T. aestivum, as reported by BIELIG and DRISCOLL (1970), is probably due largely to asynchronous replication of the chromosomes of wheat and rye. SINGH, JOSHI and SHARMA (unpublished) have observed in a cross of wheat and rye that not only there is asynchronous replication of their chromosome complements, in the presence of one dose of chromosome 5B, but the whole genomes of wheat and rye were distinctly separate within the same pollen mother cell. However, in the F1 hybrid between T. aestivum and S. cereale, where apparently the 5B gene has mutated, the genomes of wheat and rye are not separate within a pollen mother cell at the early stages of meiosis. This observation also suggests that there is pairing between wheat and rye chromosomes and would rather imply that the mutated 5B gene is responsible for the pairing of the homoeologous chromosomes of wheat and rye as well as synchronising the replication of their chromosomes. Literature cited BIELIG, L. M. and C. J. DRISCOLL 1970. Genetics 65: 241-247. NAKAJIMA, G. 1952. Cytologia 17: 144-155. (Received January 4, 1972) |