The chromosomes 4R and 6R Secale cereale cv. Imperial rye which had been received as disomic addition lines in Chinese Spring from Cambridge maintained resistance to Karnal bunt. The F1's with a highly susceptible wheat variety WL711 and BC1 to BC5 and subsequent selfed generations also maintained resistance against a particular isolate. Using the same set of wheat-rye disomic addition lines received from Kansas State University, Dhaliwal et al. (1987), however, found the rye chromosome 6R and 7R conferring resistance to Karnal bunt. The discrepancy in the identification of different rye chromosomes, 4R and 7R, of the same set of wheat-rye addition lines in the present and previous screening might have been either due to misclassification or mislabelling of 4R and 7R addition lines from different sources as there is considerable controversy over the correct identification of the two rye chromosomes. This could also have been due to different fungal isolates used for artificial inoculations in the two investigations.
The 4R and 6R chromosomes of Imperial rye have been transferred into susceptible variety following five backcrosses. About 98.4 per cent genetic background of the recipient variety WL711 has been reconstituted. The maintenance of resistance in the 4R and 6R addition lines during continuous screening in the different backcross generations against an isolate (PWB 154) unequivocally confirms that both 4R and 6R Imperial rye chromosomes carry dominant gene(s) for resistance to Karnal bunt.
The 4R and 6R monosomic addition lines are, however, susceptible to an isolate (C-21) of Neovossia indica which had shown virulence on a Karnal bunt immune triticale variety TL1210. Sources of resistance against the new virulent isolate have also been identified in the related species of Triticum and Aegilops (Pannu et al. 1994).
Acknowledgements
The authors thankfully acknowledge the financial assistance from ICAR, New Delhi, India, Sanction No. 16.18/87/- FC.II/I which made the collections, evaluations, development and utilization of alien wheat addition lines possible.
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