Under the Asian Rice Biotechnology Network funded by Asian Development Bank and coordinated by the International Rice Research Institute, attempts were made at CRRI to pyramid bacterial blight resistance genes into a high-yielding cultivar IR64. A backcross breeding strategy (Allard, 1960) was employed to transfer bacterial blight resistance genes to the recurrent parent IR64 via marker-assisted breeding strategy (Reddy et. al. 1997; Huang et al. 1997). IRBB60, in which bacterial blight resistance genes Xa4, xa5, xa13 and Xa21 were already pyramided in an IR24 background, was used as the pollen parent in crosses with IR64. Many lines were generated independently employing marker-assisted selection (MAS) with an aim of developing lines carrying bacterial blight resistance genes xa5, xa13 and Xa21 singly and in different combinations. We present here the results on the field performance of fifty genotypes generated by MAS carrying one, two or three genes for bacterial blight resistance in multi-environment tests (METs) organized at 11 locations in India under different rice ecosystems in the all-India coordinated rice improvement project. The test locations varied in

latitude, longitude and altitude. The genotypes were coded as entries (1-50) in the sense that the evaluators at different locations knew only the entry numbers. The susceptible check TN1 succumbed to bacterial blight at all the locations. Most of the entries showed a susceptible reaction at one or the other locations (Table 1). All the genotypes with single bacterial blight resistance gene xa5 or xa13 recorded resistant reaction at 5-7 locations while those with xa21 were found resistant at only 3-5 locations. Among genotypes possessing two genes, those with xa5 and xa13 showed resistance at more test sites. The genotypes possessing three genes (xa5, xa13 and Xa21) showed resistance at 5-8 test locations and were comparable in reaction to those with only two genes (xa5 and xa13, or xa5 and Xa21, or xa13 and Xa21). CRMAS 2231-2 with xa5, and CRMAS 2231-17 and CRMAS 2231-18 with xa21 showed a susceptible reaction at more locations than the check IR 64.

An earlier study clearly demonstrated the potential for gene pyramiding to develop cultivars with durable resistance to bacterial blight (Sridhar et al. 1999; Muralidharan et al. 2003). Overall, the best genotype was CRMAS 2231-29 (entry 29; xa13 + Xa21) that showed a susceptible reaction only at Pantnagar and Raipur. CRMAS 2231-22 (with xa5 + xa13), and CRMAS 2231-32, CRMAS 2231-35, CRMAS 2231-36, CRMAS 2231-37, CRMAS 2231-42, CRMAS 2231-45 and CRMAS 2231-48 (with xa5 +xa13 + Xa21) showed resistance at eight test locations.

Acknowledgement

We express our sincere thanks 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

Allard, R.W., 1960. Principles of Plant Breeding. John Wiley and Sons Inc., New York, pp. 485.

Huang, N., E.R. Angeles, J. Domingo, G. Magpanty, S. Singh, G. Zhang, N. Kumarvadivel, J. Bennet and G. S. Khush, 1997. Pyramiding of bacterial leaf blight resistance genes in rice marker assisted selection using RFLP and PCR. Theor. Appl. Genet. 95: 313-320.

Muralidharan, K., D. Krishnaveni, G.S. Laha, C.S. Reddy, M. Srinivasprasad and R. Sridhar, 2003. Appraisal of bacterial blight resistance genes in India. RGN 20: 96-98.

Reddy, J.N., M.R. Baraoidan, M.A. Bernardo, M.L.C. George and R. Sridhar, 1997. Application of marker-assisted selection in rice for bacterial leaf blight resistance gene, Xa21. Curr. Sci. 73: 873-875.

Sridhar, R., J.N. Reddy, U.D. Singh and P.K. Agarwal, 1999. Usefulness of combinations of bacterial leaf blight genes at Cuttack, Orissa, India. Int. Rice Res. Notes 24: 24-25.