Asominori is one of the international differentials used for testing the pathogenicity of the bacterial leaf blight (BLB) pathogen,Xanthomonas oryzae pv. oryzae. It has been one of the varieties most resistant to BLB in Japan since its release in 1973. Extensive testing under the JIRCAS and YAAS collaborative research project on rice genetic resources between 1994 and 1996 showed that Asominori has stable resistance to BLB in both indica and japonica rice-growing areas in Yunnan, China. Hence, Asominori is considered a useful source of durable resistance to BLB. We found that Asominori has an allele of the Xa1 locus on chromosome 4 for BLB resistance, although it has been reported to harbor Xa17 independent from Xa1.