Screening of resistant rice [Oryza sativa] cultivars or varieties against dominant races of bacterial leaf blight [Xanthomonas oryzae] in Hiroshima prefecture [Japan]

There have been several reports on the survey of physiologic races of bacterial leaf blight of rice (Xanthomonas oryzae pv. oryzae), and it was found that races I and II occurred dominantly in Hiroshima Prefecture. We screened rice cultivars or varieties preserved in Hiroshima Prefecture Plant Genebank to evaluate effective genetic resources against bacterial leaf blight race (s) I and/or II. The rice plant was inoculated by clipping method and maintained in an air-conditioned greenhouse. and then, we evaluated a grade of resistance (0-2.0: resistant, 4.1-7.0: susceptible). As the results, we found that 27 cultivars or varieties from 504 were resistant to race I. Among them, 8 were bred in Japan, 8 were Japanese natives and 11 were from foreign. We also found that 13 cultivars or varieties from 470 were resistant to race II. Among them, 5 were bred in Japan , 8 were from foreign and no natives. And then, we found that 7 resistant cultivars to both races I and II were foreign origin. The cultivars or varieties evaluated to be resistant against bacterial leaf blight in the experiments might be effective genetic resources for breeding resistant cultivars to the pathogen. In the future programs ,we also should introduce a quantitative or durable resistance gene (s) to rice cultivars in order to avoid the breaking down of the qualitative resistance.