| Transfer of rust resistance Excellent resistance to yellow and brown rusts exhibited by all. T. monococcum, and some lines of T. boeoticum, T. urartu and T. araraticum can be transferred to both bread and durum wheats through interspecific crosses. The resistance can be readily transferred to the A genome as the chromosomes of T. monococcum, T. boeoticum and T. urartu are capable of perfect pairing with those of the A genome of wheat but not with the B or D genomes (Chapman et al. 1976). The chromosomes of the B and D genomes can also be induced to pair with those of the diploid wheats in the absence of chromosome 5B of bread and durum wheats or in the presence of the ph mutant (SEARS, 1976). The information on genetic control of rust resistance in the wild diploid and tetraploid wheats whether dominant or recessive is, however, a prerequisite before initiating a programme for the transfer of resistance. If the resistance is dominant its transfer in the A genome only should serve the purpose. But if it is recessive it will have to be transferred in all the genomes of wheat and durum for its full expression for practical utilization. It will be necessary to culture the young embryos for crossing the bread wheat with the diploid wheats successfully. T. monococcum and T. boeoticum are readily crossable with durum in either direction but T. urartu can be crossed only as the male parent (JOHNSON & DHALIWAL, 1976). Aegilops squarrosa and other Aegilops spp. of Sitopsis section such as Aegilops spelotides, Aegilops bicornis and Aegilops longissima etc. should also be screened for resistance to rusts as it would not be difficult to transfer the resistance from the Aegilops spp. into wheat and durum. Literature Cited CHAPMAN, V., T.E. MILLER, & R. RILEY. 1976. Equivalence of the A genome of bread wheat and that of Triticum urartu. Genet. Res. 27: 69-76. JOHNSON, B.L. & H.S. DHALIWAL. 1976. Reproductive isolation of Triticum boeoticum and T. urartu and the origin of the tetraploid wheats. Amer. J. Bot. 1088-1096. JOHNSON, B.L. & H.S. DHALIWAL. 1978. Triticum urartu and genome evolution in the tetraploid wheats. Amer. J. Bot. 65: 907-918. JOHNSON, B.L. & J.G. WAINES, 1977. Use of wild wheat resources. Calif. Agric. 31: 8-9. MCFADDEN, E.S. & E.R. SEARS. 1946. The origin of Triticum spelta and its free threshing hexaploid relatives. J. Hered. 37: 81-89. SEARS, E.R. 1976. Genetic control of chromosome pairing in wheat. Annu. Rev. Genet. 10: 31-51. |
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