| Differential behaviour of aestivum and durum
wheats to races 77 and 106 of leaf rust (Puccinia recondita Rob.
ex Desm.) H.N. PANDEY and M.V. RAO Wheat Project Directorate, Indian Agricultural Research Institute New Delhi-110012, India Indian wheat is subject to attack by all the three rusts, although their importance and distribution varies from region to region. Three species of wheat, viz., Triticum aestivum, T. durum and T. dicoccum are cultivated in India at present. While monitoring the field virulences of these rusts, they are all considered together irrespective of the fact on which species of wheat they are found. Since most of the area is under aestivum wheats (a little over 85%), the race situation so obtained, gives information mainly of aestivum wheats only ignoring the tetraploids, namely, the durum and dicoccum wheats. The information on field virulences of rust pathogen is used as a guide line for breeding rust resistant wheats including the durum wheats. In a durum multiline programme, 10 durum parents, namely, NI 146, 'Bijaga Yellow', HD 4519, HD 4530, CC 422, CPAN 1311, CPAN 1469 CPAN 1471, CPAN 1480 and CPAN 1548 were tested for their seedling reactions against leaf rust races of India to match these reactions with the known reactions of Lr lines of T. aestivum. The behaviour of durum lines and Lr lines of aestivum to aggressive (77) and weak (106) races of leaf rust is mentioned in Table 1. Data in Table 1 show that race 106 considered to be a weak race is weak only on aestivums but aggressive on durums. Similarly race 77 considered to be an aggressive race is aggressive only on aestivums but weak on durums. Evidently no generalization can be made with regard to the status of a race as weak or aggressive as it is subject to the genotypes grown. Of the 10 durum varieties tested against races 77 and 106 of leaf rust, 7 varieties (HD 4530, CC 422, CPAN 1311, CPAN 1469, CPAN 1471, CPAN 1480 and CPAN 1548) were found to be resistant to race 77 while only 3 varieties (HD 4530, CPAN 1311 and CPAN 1469) were resistant to race 106. In case of Lr lines, the picture is just the reverse. Of the 22 Lr lines and two aestivum wheats carrying Lr 10 tested, only 4 lines (Lr 9, Lr19) Exe. (Lr 10) and Lee (Lr 10) were resistant to race 77 while 20 were resistant to race 106. To find out the presence of probable Lr genes in durum parents, seedling reactions of the 10 durum varieties to leaf rust races were matched with the known reactions of Lr lines of aestivum. Matching of reactions revealed that of the 7 durum varieties resistant to race 77, only 2 varieties (CPAN 1311 and CPAN 1469) were found to carry Lr 10 while 5 varieties did not show the presence of Lr 10 in them. Subsequently the reactions of these test varieties were matched with the known reactions of lines/varieties carrying Lr 24, Lr 25, Lr 26, Lr 27, Lr 28 and Lr 29, which give resistance to race 77 in addition to other important races/ biotypes. These genes too did not show their presence in the durum varieties. Thus other than the alien genes, Lr 10 and Lr 27 are the only known genes which impart resistance to race 77. This suggests that the Lr genes worked out in the T. aestivum background either do not hold good for T. durum or there is some other unknown gene/s responsible for resistance to race 77 in the durums. Hence, it is important to take into consideration this variable behaviour of durums and aestivums in breeding for rust resistance, in general, and to leaf rust in particular. It will also be very interesting to extend these studies to other races of leaf rust and also to stem and stripe rust races, as well. Conclusious Lr genes in aestivums and durums appear to be different for race 77. Similarly a general classification of races into weak and aggressive categories for hexaploid and tetraploid wheats together requires rethinking. Acknowledgement We thank Dr. S.D. Singh, Senior Wheat Pathologist, Wheat Project Directorate, I.A.R.I., New Delhi-12 for his critical reading of the manuscript and suggestions. |