II.12. Duplication of tandem satellites, Progress report.
P. Hagberg, The Swedish Seed Association, Savalöv, Sweden.
Some of the translocation stocks at Svalöv have been used for production of duplications according to the method suggested by Gopinath and Burnham (1956). The first viable duplication was obtained from the cross T6-7a x T6-7d (Hagberg, 1962). As a rule, the duplications have been considered to be of lower vitality than the corresponding normal karyotypes. In field trials they have somewhat shorter straw. No accurate measurements have so far been made on dose effects of genes in the duplicated segments.
Among the translocations we have two stocks carrying tandem satellites on chromosome 7, and no satellite on chromosome 6. One of them, T6-7k (T130), was induced by x-rays and the other, T6-7w (T291), by acute gamma-rays. Their karyotypes are very similar. The breaks are in the short arm of chromosome 6, near the nucleolar organizer, and in the distal part of the satellite of chromosome 7. Both stocks should give viable duplications of satellites and nucleolar organizers if crossed with T6-7ae (T412), which has tandem satellites on chromosome 6. Any differences in breakpoint position between T130 and T291 could be revealed as different plant phenotypes of the duplication stocks.
Both duplications are now isolated and found to be quite viable (Hagberg and Hagberg, 1971; Hagberg, Persson, Hagberg, 1972). Duplication plants isolated from the F2 of the cross T291 x T412 have been grown two generations in field trials and show the characteristics mentioned above. The F2 from the cross T130 x T412 was screened last year, and some of the segregating material was grown in the greenhouse. Even with the varying conditions in an ordinary greenhouse, there were tendencies though towards differences in plant height and rate of development. Homozygous duplications were heading 10 to 15 days later, and they had shorter straw at maturity than heterozygous duplications and the other variants. More information will be obtained from comparative field trials in 1974. The program also includes crosses between the two duplications to see what might be obtained. Figure 1 and 2 show metaphases of F1 and of the homozygous duplication from T130 x T412. The satellites originating from chromosome 7 are as a rule more closely attached to chromosome arms than are the satellites from chromosome 6, and could be hard to distinguish. Also the actual karyotypes are shown (Figure 3).
References:
Gopinath, D. M., and C. R. Burnham. 1956. A cytogenetic study in maize of deficiency - duplication produced by crossing interchanges involving the same chromosomes. Genetics 41:382-395.
Hagberg, A. 1962. Production of duplications in barley breeding. Hereditas 48:243-246.
Hagberg, A., and G. Hagberg. 1971. Chromosome aberrations and their utilization. Barley Genetics II.
Hagberg, A., G. Persson, and G. Hagberg. 1972. Utilization of induced chromosomal aberrations. "Induced mutations and plant improvement" IAEA, Vienna.
