In Japan, Kiyosawa (1981) analyzed blast resistance genes using seven stable blast isolates. Thirteen dominant resistance genes were identified at eight loci. Soon cultivars and breeding lines with single resistance genes were generated. Later, near-isogenic lines (NILs) in the background of Co39 possessing single gene or multiple genes in various combinations were developed at the International Rice Research Institute, Philippines (Mackill and Bonman, 1992). Some of these NILs were evaluated at six different sites in India during 1998 by Sridhar et al. (1999), who found the effectiveness of individual resistance genes in NILs to vary between locations. We present here the results on the performance of rice genotypes carrying gene(s) for blast resistance in multi-environment tests (METs) organized at 13 locations (Table 1) under different rice ecosystems in the all-India coordinated rice improvement project. The test locations varied in the latitude, longitude and altitude. NILs, international blast differentials and check rice genotypes were coded as entries (Bl-0 to Bl-28), in the sense that the evaluators at different locations knew only the entry numbers.

The multi-environment blind-tests clearly demonstrated the expression of a high degree of resistance in A57 carrying three resistance genes (Pi1, Pi2 and Pi4). A57 was identified as the best line that exhibited resistance to blast across the country in all rice growing environments,

irrespective of ecosystems. The performance of BL 245 with two resistance genes (Pi2 and Pi4) was comparable to A57. BL 122 (Pi1 + Pi2), C101A51 (Pi2), O minuta der (Pi9), and BL 142 (Pi1 + Pi4) were resistant at 11 locations but susceptible in at least two other test sites. Two other NILs, each carrying a single gene for blast resistance, namely, C101LAC (Pi1) and C105TTP (Pi4b), also recorded a broad spectrum of resistance. The performance of these NILs was marginally superior to the resistant checks (Tadukan, Rasi, Tetep and IR 64) and the international blast differential Raminad Strain 3. Alleles for the genes identified as effective and durable in the METs in this study must be located in India-bred cultivars besides discovering newer ones to effectively utilize resistance genes in future.

Acknowledgement

We express our sincere thanks to staff of IRRI, Philippines, and CRRI, Cuttack, for providing us with the required pure seeds, and to Dr. B. Mishra, DRR, Hyderabad, for encouragement and facilities. We thank all the scientists responsible for the conduct of the all-India coordinated rice pathology experiments at different locations in the country.

References

Kiyosawa, S. 1981. Gene analysis for blast resistance. Oryza 18: 196-203.

Mackill, D.J. and J.B. Bonman. 1992. Inheritance of blast resistance in near-isogenic lines of rice. Phytopathology 82: 746-749.

Sridhar, R., U.D. Singh, P.K. Agarwal, J.N. Reddy, S.S. Chandrawanshi, R.B.S. Sanger, J.C. Bhatt, Y. Rathaiah K.V.S.R.K.Row. 1999. Usefulness of blast resistance genes and their combinations in different blast-endemic locations in India. Int. Rice Res. Notes 24: 22-24.