An elite indica rice variety, 'IR72', was transformed with a cloned gene, Xa21, through particle bombardment. Molecular analysis of transgenic plants revealed the presence of a 3.8-kb EcoRV-digested DNA fragment corresponding to most of the Xa21 coding region and its complete intron sequence, indicating the integration of Xa21 into the genome of 'IR72'. In the T1 generation, the transgene was inherited and segregated in a 3:1 ratio. After inoculation with the prevalent races 4 and 6 of Xanthomonas oryzae pv. oryzae (Xoo), T1 plants positive for the transgene were found to be resistant to bacterial blight (BB). We also observed that the level of resistance to race 4 of Xoo was higher due to the pyramiding of Xa21 and Xa4 present in 'IR72'. Since the inactivation of the transgene Xa21 occurred in the two transgenic T1 plants, a larger progeny should be obtained for selecting homozygous line with a consistently higher level of resistance to the BB pathogen
