Identifying and mapping a new gene for bacterial blight resistance in rice based on RFLP markers

Bacterial blight, caused by Xanthomonas oryzae pv. oryzae, is one of the most serious diseases of rice worldwide. We previously identified a rice cultivar, Zhachanglong, from Yunnan Province in southwest China that showed resistance to all 10 X. oryzae pv. oryzae strains tested. The objectives of the current study were to assess the identity of the gene in Zhachanglong and to determine the chromosomal location by restriction fragment length polymorphism (RFLP) mapping. We found that the resistance of Zhachanglong to bacterial blight is controlled by a dominant gene that is not allelic to Xa1, Xa2, Xa4, or Xa14. The new gene is linked to the Xa4 locus, with a recombination frequency of 13.3 +/- 4.5%. RFLP analysis resolved this gene to the end of the short arm of chromosome 11 in the rice linkage map, confirming the distinctness of this gene from all the known genes for bacterial blight resistance. We also found that this new gene is resistant to a broad range of X. oryzae pv. oryzae strains. We tentatively designated this gene as Xa22(t).