Comparison of the Reactions of Rice and Wheat Seedlings to Infection of the Causal Fungus of the “Bakanae” Disease and to Filtrates of its Cultures

Abstract

The occurrence of physiologic specialization in the causal fungus of the “Bakanae” disease of rice has already been observed by several authors. Certain strains of the fungus have the power to cause strongly the overgrowth of rice seedlings, while some others check their growth. There are undoubtedly some strains which show the intermediate character as to the growth-promotion of the host plant. Moreover, from previous investigations it is clear that the causal fungus isolated from rice seedlings is capable of attacking several other plants and causing their characteristic overgrowth. On the other hand, some investigators have carried out the interesting experiments, showing that the filtrate of cultures of a certain strain of the causal fungus is able to produce the phenomenon characteristic of the “Bakanae” disease in the absence of the mycelium. Consequently, the writer treated the overgrowth property shown by the presence of the causal fungus, distinguishing from the similar property shown by its absence. The latter is called “virulence” in the present paper, as compared with the proper pathogenicity.The present paper deals with the results of the writer's investigations carried out in order to solve the following two problems.1. Whether the tendency in the extent of pathogenicity shown by a strain is similar or not to that of virulence shown by the same strain.2. Whether the tendency in the extent of pathogenicity as well as of virulence for other plants is similar or not to that for rice seedlings.From repeated experiments the writer recognized safely the following conclusions.1. Both the pathogenicity and the virulence in the causal fungus of the “Bakanae” disease of rice seedlings are different in their extent according to strains, as has already been reported by the previous investigators.2. The pathogenicity and the virulence shown by a strain have a similar tendency in their extent.3. The data obtained in repeated experiments with wheat seedlings showed that the tendency in the extent of pathogenicity as well as of virulence for that plant seems to be quite parallel to that for rice seedlings.