Objective The purpose is to screen rice varieties with resistance to the V and IX pathotypes of Xanthomonas oryzae pv. oryzae (Xoo).

Method Ninety-seven brown planthopper resistant rice varieties collected from tropical and subtropical areas were surveyed against V and IX types of Xoo. The leaf-cutting inoculation method was used to identify the resistance level of rice varieties to bacterial blight at the seedling and adult stages. A mapping population was developed for a variety with excellent resistance performance, which was applied to map and clone the resistance genes.

Result Twenty and eight rice varieties were detected to be resistant to V type at the seedling and adult stages respectively, and four varieties showed moderate or high resistance at both stages. Moreover, thirty-four and nine rice varieties were identified to be resistant to IX type at the seedling and adult stages respectively, and one variety showed moderate or high resistant level at both stages. Rice variety ‘BX02’ showed excellent resistance to V type of Xoo at both stages. Therefore, one F₂ mapping population was developed by crossing ‘BX02’ with ‘9311’, and the resistance locus was identified on chromosome 5 with the logarithm of adds (LOD) score of 40.6. This mapping interval contained the cloned xa5 gene with resistance to V type of Xoo. Sequence amplification analysis confirmed that it was the bacterial blight resistance gene xa5.

Conclusion Four and one varieties were detected to be resistant to V and IX types of Xoo at both stages respectively, which provides materials for rice resistance breeding against the bacterial blight.