Abstract
1) In this paper are given results of comparative studies on various strains of Helminthosporium Oryzae Breda de Haan, causing leaf-spot disease of rice in the Pacific regions, Compariosns were especially made between the Japanese and the American strains, which produced the spores in cultural conditions.
2) The lesions on the rice plant, produced by both the Japanese and the American strains, are similar in general appearance.
3) Both the strains show clear contrasts in the morphological characters, especially in the shape of spores. The spores of the Japanese strain are obclavate, broadest at the point of one third from the base, provided with pretty large, prominent hilum. While those of the American strain are cylindrical or fusiform, broadest at the middle part or the point of two thirds from the base, curved to one side regularly, the hilum being small and less prominent. The general shape of the spores of the latter is much more slender than the former.
4) Not only morphologically but also physiologically the both strains show differences between them.
5) The both strains were inoculated on the seedlings of about 480 varieties or strains of cultivated rice. The results show that there are no great divergence between both strains regarding the pathogenecity to the rice seedlings.
6) The above stated two strains must be regard as quite distinct forms, and may possibly be different species.
