2017 年 2017 巻 64 号 p. 15-17
An inoculation method for confirming the pathogenicity of Pseudomonas syringae pv. japonica (synonym pv. syringae), causal agent of bacterial black node of barley and wheat was developed. The plants at flag leaf stage were each placed at 20-25 ℃ for about five hours in a dark container, then 10 µl bacterial suspension was dropped on the auricle at several points in time around the stage. The inoculated plants were placed at 20-25 ℃ for three days in a dark container and then placed for one week with appropriate light and humidity. The infection frequency by this inoculation method was the highest on the plants inoculated during flag leaf expansion stage, while it decreased when the plants were inoculated at the beginning of heading stage. When plants of 14 cultivars of wheat and 11 cultivars of barley were each inoculated with the pathogen during flag leaf expansion stage, disease symptoms were formed on all the cultivars. These results suggested that wheat and barley were more susceptible to bacterial black node pathogen during flag leaf expansion stage irrespective of cultivar type. The disease mainly occurred on the leaf sheath as withering with black lesions forming under the inoculated point, but several plants also showed black lesions on the stem, followed by stem breaking, as well as ear burn. These symptoms are identical with those found in the field, indicating that bacterial black node disease can be reproduced by the inoculation method.