| Origin of Triticum zhukovskyi H.S. DHALIWAL and B.L. JOHNSON Department of Plant sciences, University of California, Riverside, CA 92502, U.S.A. The parentage of a polyploids of recent origin can be confirmed if the hybrid involving the polyploid and the synthetic amphiploid between its presumable parents is fertile. This has been accomplished in the case of T. aestivum ssp. spelta (MCFADDEN and SEARS 1944). Evidence from karyotype studies (UPADHYA and SWAMINATHAN 1963) and protein electrophoresis (JOHNSON 1968) suggested that T. zhukovskyi (AzAzAtAtBtBt) presumably originated as an amphiploid between T. timopheevi (AtAtBtBt) and T. monococcum (AA). However, this has not been established unequivocally by artificial synthesis of T. zhukovskyi. WATANABE et. al. (1956) synthesized the T. timopheevi - T. monococcum amphiploid but it was not test crossed with T. zhukovskyi. Subsequent attempts to synthesize T. zhukovskyi were unsuccessful (UPADHYA and SWAMINATHAN 1965). In this article we are reporting chromosome pairing and fertility of synthetic amphiploids involving T. araraticum (wild prototype of T. timopheevi) and T. boeoticum (presumed wild prototype of T. monococcum), and F1 hybrids between the amphiploids and T. zhukovskyi. Results reported here confirm the previous finding that T. zhukovskyi originated as an amphiploid between T. timopheevi and T. monococcum. Materials and Methods To synthesize the amphiploids, triploid hybrids were made between T. araraticum (1767, 2659) and T. boeoticum (1815, 2578) instead of between their cultivated types T. timopheevi and T. monococcum In order to induce polyploidy the seedlings of the araraticum x boeoticum triploid hybrids were treated by dipping their plumules into 0.4% aqueous colchine solution for 45 minutes. Alternatively, seedlings (0.5 cm plumule) were treated with nitrous oxide gas for 24 hrs. at 8 atmospheres pressure and were transplanted directly into the soil. Two of the three araraticum-boeoticum amphiploids were crossed with T. zhukovskyi (986). Sporocyte material was fixed in Cornoys fluid (6:3:1) for 8 hrs. and anther squashes were made in 1% Propiono-orcein. Chromosome association was scored from meiotic metaphase I cells. Results and Discussion Results of chromosome association and fertility of T. zhukovskyi. T. araraticum x T. boeotocium hybrids, araraticum-boeoticum amphiploids and F1 hybrids between T. zhukovskyi and the amphiploids are given in Table 1. A high frequency of multivalents in T. zhukovskyi (0.35 III+1.35 IV) indicates that it is not completely diploidized like other polyploid wheats. The multivalent association could be attributed to homologous pairing presumably between its two similar A genomes. However T. zhukovskyi is more diploidized than would be expected if it had two similar genomes particularly since it is believed to be of recent origin. Furthermore, the possibility that the multivalents represent homoeologous association can be eliminated as T. zhukovskyi apparently inherited a Ph gene system from its tetraploid parent equally as efficient as that of T. aestivum (FELDMAN 1966). which completely suppresses homoeologous association. |
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