Various methods for testing blast resistance of rice varieties were compared by drawing a correlation diagram of each pair of the methods. In all the diagrams drawn, curvilinear regressions were observed. This indicates that the level of estimation of resistance is different between two methods compared, and that there are upper and lower limits of measurable range in all the methods. By injection method the resistance of varieties belonging to intermediate reaction classes was estimated to be more susceptible than by spraying method for inoculation. In spraying method, intermediate varieties were judged to be more resistant by the evaluation based on the type of predominant lesions than by the evaluation based on the type of the largest lesion. Intermediate varieties showed more resistant reaction by inoculation at the 4 week stage than at the 2 week stage of rice seedlings, and by inoculation with Ken 54-04 than with Ken 54-20. Interrelations among these phenomena were schematically shown in one figure (Fig. 11).
A part of field resistance which cannot be detected in the greenhouse by the usual method for differentiating pathogenic races could be tested by the following methods: 1) lowering the measurable range of testing method by using a less aggressive fungus strain, 2) increasing the resistance of varieties by increasing plant age, or by growing plant under conditions similar to field conditions.