1. The writer has reported the results of the investigations on the influence of sunlight upon the lesion enlargement of the rice blast disease in the previous paper. The present paper deals with the results of the similar experiments with the Helminthosporium disease of rice seedlings. 2. In the experiments, the writer used the glass boxes and the cages made of wire-netting kept under the approximately same condition except light intensity. The potted rice seedlings were kept in the boxes or cages uncovered, coverd with a single or two sheets of white cotton cloth and also with two sheets of black cloth as soon as they had been taken out from the inoculation chamber. After previously determined intervals the sizes of the diseased lesions were measured under microscope. 3. The lesion enlargement in the early stage of the interception of sunlight seemed to be maximum on the seedlings kept under the darkest condition and minimum on those in the uncovered boxes and cages. This point is not identical with the case of the rice blast disease, in which in the same stage the lesion enlargement was maximum under the medium degree of shading. 4. In the late stage, the lesion enlargement of the Helminthosporium disease changed to be maximum on the seedlings kept under the medium degree of shading. In the case of the rice blast disease, it was, however, maximum in the uncovered boxes. 5. The sunlight has a tendency to retard the growth of the causal fungus on culture media. This is quite similar to the case of the blast disease. 6. The relation of sunlight to the lesion enlargement of the Helminthosporium disease in the late stage was shown to be homologous to that of the blast disease in the early stage. In all probability the disagreement of the results by these diseases is due to the difference of the sensibility of the causal fungi to the host vitality.
1. This paper deals with the results of the writer's investigations on the Sclerotium disease of bananas caused by Corticium centrifugum (LÉV.) BRES. Comparative studies of the causal fungus with five strains of the same fungus isolated from various plants were first carried out. The pathogenicity of the causal fungus, the effects of certain environmental factors on the growth of the causal fungus and the control method of this disease were also studied. 2. So far as the writer's experiment concerned, the causal fungus from bananas seems to be nearer to the strain isolated from the rocambole than the strain from the clover. 3. Under favourable conditions either the hyphae or the sclerotia of the causal fungus are capable of attacking the wounded or unwounded fruits of bananas. 4. The optimum temperature for the germination of the sclerotia of the causal fungus seems to lie in a wide range between 24° and 36°C. and they require the relative air-humidity higher than 97% for germination. According to the writer's experiment the air-humidity seemed to be a more important factor for the sclerotial germination than the air-temperature. 5. The optimum temperature for the mycelial growth of the causal fungus seems to lie at from 28° to 32°C. The growth is remarkably diminished at 20°C., and shown scarcely at ca. 11°C. 6. The control method of the disease in question may be as effective with the refrigerated transport by rapid cooling of ca. 11°C., as in the case of other diseases of the banana in transport.
Thirty-two colony variants were obtained from the two different strains of Bacterium malvacearum which were isolated from the angular spots of cotton at Taihoku, viz. 9 variants (A-I in fig. 1) from culture strain 427 and 23 variants (A-W in pl. II) from culture strain 450. All the variants derived from the former are resistant to the phage which was isolated from the diseased leaves by MATSUMOTO and HUZIOKA, (4) while any of the latter are susceptible to it, though somewhat different in susceptibility and size. of plaque produced, generally more susceptible variants producing larger plaques (table 6). The plaques produced on the cultures of variants E, J, and M enlarge to a great extent with the increase of the incubation period (table 6). The phage in question proved to be consisted of at least two elemental phages. The one is active against all the variants, and the other is only active against those except E, J, M, O, and P variants (tables 7-8). The size and number of plaques are more or less decreased with the increase of the amount of bacteria used (table 11). The same is true with the temperature within a certain limit, although in this case the effect is more remarkable on the number of plaques. Resistant strains developed from the phage-bacterial cultures are not apparently different in morphological characters from their original susceptible bacteria.